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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 147
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 149
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 150
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 151
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 152
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 153
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 154
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 155
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 156
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 157
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 158
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 159
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 160
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 161
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 162
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 163
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 164
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 165
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 166
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 167
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 168
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 169
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 170
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 171
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 172
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 173
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 174
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 175
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 176
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 177
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 178
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 179
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 180
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 182
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 183
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 184
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 185
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 186
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 187
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 188
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 189
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 190
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 191
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 192
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 193
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 194
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 195
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 196
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 197
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 201
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 202
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 203
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Page 204
Suggested Citation:"VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT." National Research Council. 1968. Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson. Washington, DC: The National Academies Press. doi: 10.17226/18636.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

VISION PROBLEMS IN LOW-ALTITUDE, HIGH-SPEED FLIGHT Introductory Remarks by the Chairman James W. Miller Engineering Psychology Branch Office of Naval Research The papers presented in this Section describe current work re- lated to the visual aspects of low-level, high-speed flight, and include such topics as geographic orientation, visual acquisition and tracking, tactical strike missions, and low-level problems associated with helicopters. The concept of flying at extremely low altitudes in order to penetrate enemy territory is by no means a new one. However, recent advances in radar defense systems and the accuracy of guided-missile systems have made it impera- tive that attacking aircraft avoid early detection, if at all possible, in order to insure survival. There are several types of missions which require flying at these extremely low altitudes. Such mis- sions are usually concerned with visual reconnaissance, ground support, special-weapons delivery, or fire control. The Low-Altitude High-Speed (LAHS) mission requires pre- cise location and identification of ground points with precise heading, air-speed, and altitude. Such navigation is a combina- tion of dead reckoning, and visual and radar navigation using ground features as an aid in the identification of targets and checkpoints. Terrain-avoidance radar and other airborne dis- play systems are being developed in order to aid the pilot in such missions. Recent evidence indicates, however, that, in large numbers of flights, the pilot becomes so geographically disoriented that the goal is not achieved at all and the entire mission must be aborted. It is hoped that these papers will clarify those problems which currently face pilots flying such missions. 145

GEOGRAPHIC ORIENTATION DURING LOW-ALTITUDE FLIGHT1 James J. McGrath Human Factors Research, Incorporated Los Angeles, California In low-altitude flight, the pilot is burdened with a large number of information and performance requirements. One of these requirements, that he maintain an awareness of his navigational position, has become known as "geographic orientation." (Geo- graphic orientation should not be confused with the more familiar spatial orientation, which generally refers to the pilot's aware- ness of the attitude of his aircraft.) Before undertaking any extensive research on geographic orientation, it was first necessary to determine the need for re- search in this area and the directions it should take. Therefore, in June, 1963, a "Phase 1" effort began. It was essentially a problem analysis effort, rather than a problem solving effort. The purposes of the research were: first, to determine whether pilots under operational conditions become lost frequently enough to constitute a significant cause of mission failure; secondly, to determine the role for research and to establish the priority of research problems within this area: and, finally, to evaluate pos- sible experimental techniques to be used in solving the research problems. The inquiry was limited during this phase to those missions in which the pilot must fly at low altitudes under visual flight rules. 1. This research is being supported under Contract Nonr 4218(00) by the Joint Army-Navy Aircraft Instrument Research project, a coopera- tive effort of the Office of Naval Research, The Bureau of Naval Weapons, and the U.S. Army Material Command. 146

THE OPERATIONAL PROBLEM The first task of the project was to determine the magnitude of the problem of geographic disorientation in present-day aviation operations. The guiding principles in carrying out this task were: (a) the magnitude of the problem of geographic disorientation should be documented by objective data, rather than by personal opinion: (b) the data should come from several different sources, rather than from a single source: and (c) the data should be cur- rent to reflect conditions found in present-day aviation. Aircraft Accidents An obvious indication of the magnitude of the problem would be the number of aircraft accidents attributable to geographic dis- orientation. Therefore, aircraft accident records were obtained from the Air Force, Navy, Army, and Civil Aeronautics Board and were examined to determine the role of geographic disorien- tation in aviation safety. Fig. 1 shows the number of aircraft completely destroyed and the number of lives lost in major aircraft accidents attributable to geographic disorientation in military aviation during the years 1958 to 1962. The tabulation does not include accidents in which the aircraft sustained reparable damage, nor those in which the crew were only injured. Accidents in which geographic disorien- tation played only a minor or inconsequential role were also excluded. In civilian aviation during the three-year period 1959-1961, a total of 243 accidents resulted from the pilot becoming lost under Visual Flying Rules (VFR) conditions. In these accidents 41 per- Q60 u 550 K « 40 u !» u. 2 20 u 5 10 ^ USAF USN USA 60 50 2 40 20 10 0 USAF USN USA FIG. 1. Number of aircraft destroyed and men fatally injured in aircraft accidents attributable to geographic disorientation in military aviation, 1958-1902.

sons were killed. Many pilots became lost because they continued VFR into Instrument Flying Rules (IFR) weather conditions. Dur- ing the same three-year period, 613 accidents resulted from this type of geographic disorientation, and 365 of these involved fa- talities. Geographic disorientation was a contributing cause of 6.7 per cent of all general aviation accidents during the period studied. Although aircraft accidents resulting from geographic dis- orientation have taken a heavy toll of aircraft and human lives, such aviation safety data do not accurately reflect the frequency with which pilots have become lost. The vast majority of pilots who become lost survive the experience, and accident statistics describe only a minor aspect of the problem. Personal Experiences of Military Aviators Another source of data was the pilot himself. A total of 72 Navy, Marine Corps, and Army pilots was asked to describe their most serious personal experiences with geographic disorientation. All but four pilots described at least one instance of becoming lost in flight; the majority said they had had many such experiences. Forty-five of these descriptions of critical incidents were re- corded in detail. One of the items of information recorded was the date on which the incident occurred. Fig. 2 shows the distribution of critical incidents by calendar year, and Fig. 3 shows the distribution by month within the year 1963. Note that the most frequent category was 1963; and within that year, most of the incidents occurred during July—the month 63 62 61 60 59 58 57 56 55 54 53 FIG. 2. Forty-five critical in- cidents of geographic disori- entation reported by military aviators, distributed by calen- dar vcar. 148

JULY JUNE MAY APR MAR FEB MONTH. 1963 FIG. 3. Twenty-two critical incidents of geographic disorientation re- ported by military aviators, distributed by calendar month during 1963. during which the interviews were conducted. One may draw either of two conclusions from the data: that an epidemic of geo- graphic disorientation occurred in July, 1963, or that geographic disorientation is a relatively common occurrence among military aviators. When asked to relate his most serious personal experi- ence of being lost, the pilot simply relates his most recent one— usually an experience which has occurred within the past few months. Flight Assists to Lost Civilian Aviators The large number of civilian aviators who become lost is indi- cated by the Flight Assist Reports issued by the Federal Aviation Agency (FAA). In 1962, a total of 1,492 assists was given by ground control operators to pilots flying the federal airways system. Of this number, 1,270 assists were given because the pilots were lost. In other words, of all the pilots who required assistance for all reasons, 88 per cent required assistance be- cause they were geographically disoriented. This is a conserva- tive number, according to FAA officials. They believe that assist- ing lost pilots to reorient themselves is such a commonplace event in air traffic control that a great many such incidents go unreported. Geographic Disorientation on Low-Altitude Missions To get closer to the heart of the military problem, attention was turned to the low-altitude attack training missions which are now being flown over the Sandblower courses. (Sandblower courses are those routes designated for low-level training and extend from the Northwest to the deserts.) These missions are assumed to be representative of operational combat missions flown by light attack aircraft. Mission critiques of almost one thousand Sand- 149

blower flights were analyzed. Based on the statements of the chase pilots, who evaluated the missions, Fig. 4 shows the inci- dence of geographic disorientation on these flights. Ten per cent of the missions failed completely because the pilot became lost. In another 17 per cent of the missions the pilot became lost, but eventually reoriented himself and found the target area. In these cases the mission was compromised in many ways, and under combat conditions might have failed. The remaining 73 per cent of the missions were categorized as "O.K." Many of these mis- sions failed too, but not because of geographic disorientation. FIG. 4. Summary of data obtained from 959 flight critiques of low-level navigation training missions. It is important to point out that the "abort" and "recover" percentages are minimum figures, in that many cases of disori- entation went unreported, and any case that was doubtful, or that had insufficient information, was thrown into the "O.K." category. Records of Individual Pilots To clarify the data obtained from the flight critiques, a study of individual differences in low-altitude navigational performance was made. A "probability of disorientation" was computed for each pilot, based on the proportion of his flights on which he be- came geographically disoriented. The frequency distribution shown in Fig. 5 was plotted from the resulting data. The distri- bution includes 126 pilots, each of whom flew between six and 150

PROBABILITY OF DISORIENTATION FIG. 5. Frequency distribution of disorientation incidents showing in- dividual differences in geographic orientation performance. eleven low-altitude navigational missions. Individual differences ranged from becoming lost on no mission to becoming lost on every mission. For the reasons mentioned earlier, these data are conservative estimates of the frequency of geographic dis- orientation on these missions. The data can be interpreted more meaningfully in the form shown in Fig. 6, which is a cumulative distribution of the data shown in Fig. 5. The abscissa represents probability of dis- orientation based on the percentage of missions on which the pilot became lost. The ordinate represents the percentage of pilots who exceeded that probability. By drawing a line horizon- tally from the 50 per cent point on the ordinate to the cumulative distribution function, and, thence, vertically to the abscissa, for example, it can be seen that one-half of the pilots became geo- graphically disoriented on at least 23 per cent of their missions. By intersecting the function at another point, as another example, it can be seen that 15 per cent of the pilots became disoriented on about one-half of their missions. When individual differences in performance are of the magni- 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 PROBABILITY OF OISORIENTATION (Pd> FIG. 6. Percentage of pilots exceeding a given probability of geographic disorientntion (N = 126) 151

tude shown here, it is always valuable to know the reliability of such differences. To estimate the reliability of individual dif- ferences in geographic orientation performance the correlation was computed between the instances of disorientation that oc- curred on each pilot's even-numbered flights with those which occurred on his odd-numbered flights. The correlation coeffi- cient was 0.56. This is a remarkably high reliability coefficient in view of the nature of the data from which it was derived. Conclusions The results of the initial investigation showed that aircraft acci- dents caused by geographic disorientation take a significant toll of aircraft and human lives. But the reports of critical incidents by military pilots and the large number of flight assists to lost civilian pilots indicate that geographic disorientation is far more prevalent than indicated by accident data. If the training opera- tions that are conducted on the Sandblower courses by light attack aircraft are at all representative of low-altitude combat missions, it can be expected that a substantial number of such missions will fail, or will be seriously compromised by geographic disorienta- tion. Further, the problem is not confined to a small number of disorientation-prone pilots, but appears to be a general problem encountered by the majority of pilots. One is compelled to con- clude that the answer to the original question was "yes": geo- graphic disorientation does occur frequently enough in present- day aviation operations to affect significantly the success of those operations. THE ROLE FOR RESEARCH It does not suffice to point out the existence of a problem and to suggest vaguely that something be done about it; therefore, the next task of the project was to delineate the role for human per- formance research in the study of geographic orientation. Statistical Description of the Problem Situation The first step was an attempt to provide a statistical description of actual incidents of geographic disorientation. The data were derived from accounts of critical incidents of geographic dis- orientation as related by 72 military pilots. Fig. 7 shows some of the functions that were obtained. Fig. 7(A) shows the frequency of disorientation as a function of the number of miles from the point of the take-off to the point at which the pilot realized he was 152

(A) 100 200 3OO 400 MILES FLOWN SINCE TAKE-OFF IBI 20 30 40 MINUTES SINCE LAST CHECKPOINT (90) (0 I0 20 30 40 50 DURATION OF DISORIENTATION [MINUTES) (120) (D) (75) mm^^mmm^ 20 30 40 MILES OFF COURSE FIG. 7. Frequency (f) of geographic disorientation in- cidents as function of (A) miles flown since take-off; (B) minutes since last identified checkpoint; (C) dura- tion of disorientation episode; and (D) miles off course during disorientation episode. lost. Disorientation incidents occurred about equally often at all distances from less than 50 miles to more than six hundred miles from the point of origin. In other words, the occurrence of geo- graphic disorientation was not systematically related to distance flown, and it appears that geographic disorientation can overtake the pilot at almost any stage of a flight. Fig. 7(B) shows the frequency of disorientation as a function of the amount of time that had elapsed since the last identified checkpoint. Again, the range was very large. It is particularly interesting to note that a number of pilots became disoriented only a few minutes after they had fixed their positions with an identified checkpoint. Fig. 7(C) shows that the durations of the disorientation ex- periences ranged from about 4 minutes (min) to more than an hour. The median duration was 12 min which, in an aircraft, is a dangerously long period of confusion. 153

Fig. 7(D) shows that during these episodes of geographic dis- orientation the pilots were anywhere from 4 or 5 miles to 75 miles from their intended track. The median distance the pilot got off course during these incidents was 20 miles, which is quite a large enough error to compromise most aircraft missions, although at least one incident is known in which the pilot was seven hundred miles off course. The study also disclosed that in one-third of these cases the pilot experienced marked disbelief of some informational source during the disoriented state. That is, he became incredulous of his chart, his instruments, or his preflight planning. Most of the pilots experienced great difficulty in recognizing the fact of dis- orientation, and, having recognized it, experienced marked emotional stress. It was also noted that the pilots used different methods of re- orienting themselves. Of the pilots studied, 27 per cent first searched the chart for possible checkpoints and then attempted to locate these points in the visible field; another 43 per cent first selected terrain features that they could see and then at- tempted to locate these on the chart, while others (30 per cent) used a combination of these methods. In all cases the pilot attempted to relate some feature or combination of features in the visible terrain to features portrayed on his chart. The point of interest here is that the operational procedure recommended by Naval training doctrine is the chart-to-terrain method, the method used by the minority of pilots. A statistical analysis was also made of the aircraft accident data. Although the circumstances surrounding the accidents were diverse, the accidents themselves were easily classified by type. Fig. 8 shows the different types of aircraft accidents that re- sulted from geographic disorientation in military aviation. More than half of these accidents occurred when the pilot believed him- self to be in one position when, in fact, he was many miles away from that position. Unaware of this disorientation, the pilot sub- sequently collided with an elevated portion of the terrain. In the remainder of the cases, the pilot was well aware of the fact that he was lost, but was unable to reorient himself before fuel star- vation occurred. Depending on the circumstances, he either abandoned the aircraft or attempted an emergency landing. In addition to the predominant behavior pattern of failing to recog- nize the fact of disorientation, there was another frequently ob- served pattern. In these cases, the pilots recognized they were lost, but were reluctant to admit this to anyone, and exhausted 154

ABANOONED AIRCRAFT 31% FIG. 8. their fuel in an attempt to get out of what they considered to be an embarrassing situation. In civilian aviation these patterns of pilot behavior also occur. But, by far the dominant pattern in civilian accidents caused by geographic disorientation is the inadequacy or complete lack of preflight planning. The General Problem Areas These statistical analyses provided useful background informa- tion on the problem of geographic disorientation, but the identifi- cation of research problems came from an exhaustive study of all available informational sources. Some of the sources have already been described: aircraft accident reports, critical inci- dent reports, flight assist reports, and the critiques of low- altitude missions on the Sandblower courses. Those four sources of information provided data on actual cases of geographic dis- orientation. Two other sources of information were consulted, both dealing with pilot opinion. The two additional studies involved personal interviews conducted with 109 pilots who are presently flying low-altitude missions, and a questionnaire survey of 305 U.S. Army aviators. The large number of specific research re- quirements that were identified from the analysis of all available data has been reported in detail in a technical report (McGrath and Borden, 1963). The following six general problem areas were identified in 155

the analysis, and their relative contributions to geographic dis- orientation are indicated by the different sources of information. 1. Visual reference: Included problems dealing with the selec- tion, detection, and identification of visual checkpoints. 2. Dead-reckoning (D.R.) procedures: Included problems re- lated to the control of the aircraft and the execution of a flight plan. 3. Charts: Included problems concerned with the selection and encoding of information in aeronautical charts, problems of interpreting chart information, and problems of displaying and handling the charts. 4. Weather conditions: Included problems dealing with the influence of visibility and wind conditions on geographic dis- orientation. 5. Preflight procedures: Included problems involved in pre- flight planning. 6. Instruments (Inst.): Included problems concerned with the display and interpretation of those flight instruments which the pilot uses in navigation. The Problem Hierarchy To determine the problem hierarchy, and thus to establish the research priorities of the different problem areas, three inde- pendent studies were made of the relative contribution of the six factors to geographic disorientation. In 135 cases of disorientation on the Sandblower missions, the chase pilot clearly stated what he considered to be the cause of disorientation. These cases were tabulated by problem area as shown in Fig. 9. The results suggested a hierarchical order of problem areas with visual reference problems being dominant. The hierarchy of problem areas was verified in the second study, which was based on 108 reports of critical incidents of geographic disorientation as personally experienced by military pilots of fixed-wing and rotary-wing aircraft. None of the pilots in the second study was from the group represented by the Sand- blower mission critiques, making this an independent sample. Further, these missions covered a wide range of circumstances as opposed to the relatively standardized missions of the Sand- blower series. The causes of disorientation in 108 incidents were categorized in the same manner as the mission critiques. The results (Fig. 10) show a close agreement between the problem hierarchy as shown by critiques of standardized missions, and as shown by the personal experiences of pilots on a wide variety 156

PREF.U6HT **_ D. fi PROCEDURES 19% FIG. 9. Causes of 135 cases of geographic disorientation on Sandblower routes, classi- field by problem area. FIG. 10. Causes of 108 critical incidents of geographical disorientation in personal ex- periences of military pilots, classified by problem area. 157

of missions. About the only important difference is the greater incidence of weather conditions as a factor in disorientation as shown by the critical incident data. A third assessment of the problem hierarchy was made pos- sible by the response data obtained from the questionnaire sur- vey. In one question the 305 Army pilots were asked to give their opinion of the factors contributing to geographic disorientation. The results (Fig. 11) show a problem hierarchy highly similar to that indicated by mission critiques and critical incident re- ports. The major difference is that the Army pilots regarded preflight planning as playing a more important role in geographic disorientation than either of the other two sources would indicate. FIG. 11. Causes of geographic disorienta- tion as indicated by opinions of 305 U.S. Army pilots. The Role of Visual Checkpoints in Geographic Orientation Since all three sources indicated that visual-reference problems played a key role in geographic orientation, a study designed to clarify this role was conducted. Seventy-five pilots were shown a plan view of a hypothetical low-level VFR flight (Fig. 12). Letters indicated checkpoints, and numbers indicated time-ticks set at 2-min intervals. Checkpoint E was a turning point. The pilots were asked to assume that they had positively identified all checkpoints with the exception of G and H. which they had 158

10 l2 14 16 IB 20 22 LETTERS REPRESENT CHECKPOINTS, NUMBERS REPRESENT 2-MINUTE INTERVALS OF TIME. ASSUME ALL CHECKPOINTS ARE POSITIVELY IDENTIFIEO, EXCEPT POINTS G ANO H WHICH ARE MISSEO. FIG. 12. N* 73 PILOTS ^T 1 s -«U> S-J ^ j >^ %4-V s» >svl J^ VJ trur -S 2 1 6 8 10 l2 l4 GIN i ® ® © T l6 l8 20 22 24 26 28 30 32 34 36 38 40 42 1 t t t TURN MISSED MISSED DESTINATION © © © © ® ® _^1_ N y FIG. 13. missed. Using a rating scale, the pilots then indicated for each time-tick what their level of awareness of position would be on such a hypothetical flight (Fig. 13). The scale referred not to the pilot's ability to calculate his position, if he had to; but, rather, to his awareness of his navigational position at each point in time. The results showed that the pilots felt they would be precisely oriented only when they had positively identified a checkpoint. Immediately thereafter, awareness of navigational position would deteriorate until the pilot recovered his orientation by identify- ing the next checkpoint. As would be expected, when a checkpoint is missed, instead of recovering, there would be a sharp drop in position awareness, which would recover upon eventually identify- ing a checkpoint. It should be noted that the pilot does not con- sider himself to be lost between checkpoints, but rather his appre- hension of his precise position becomes less and less certain. The pilots were also asked to shade in those portions of the 159

N = 73 PILOTS ® © 8 10 ORIGIN FIG. 14. © © © ® © l8 20 22 24 26 28 30 32 34 36 38 40 42 1 f t 1 TURN MISSEO MISSEO 0ESTINATION flight during which they would be most attentive to the external terrain. The results indicate that the pilot is most attentive to terrain features when a checkpoint is imminent (Fig. 14). If he successfully identifies the checkpoint, he immediately turns his attention to other matters. If he misses the checkpoint, he be- comes very much occupied with searching the visual terrain until he does identify a checkpoint. Taken as a whole, the results of the study support the earlier findings that checkpoint detection and identification play a key role in geographic orientation, and an understanding of geographic orientation could be advanced most rapidly by the study of con- ditions affecting the pilot's visual-reference behavior. THE RESEARCH PROGRAM Thus far in the study, the magnitude of the problem of geographic disorientation in contemporary aviation had been established and the important problem areas identified. The next step was to evaluate experimental techniques which could be adapted to the study of these problems, and to formulate a systematic research plan. As shown in the outline in Fig. 15, the program of research began with survey studies designed to structure the research task. These are, in fact, the studies reported herein. The next step is to conduct laboratory studies to test the hypotheses de- veloped in the first phase. In evaluating various experimental techniques, it was found that there are two requirements of pri- mary importance. One is the need for fidelity of visual cues—that is, the method should provide visual stimuli which are comparable to the visual conditions in the real-world situation. Secondly, 160

SURVEY STUDIE 1 FOR VISUAbCUE FIDELITY •VISUAL REFERENCE •CHART INTERPRETATION •WEATHER-VISIBILITY • INDIVIDUAL DIFFERENCES FOR PILOT MOBILITY • DR. PROCEDURES • PREFLK3HT PLANNING • INSTRUMENT PROBLEMS • WEATHER-WIND • NDMDUAL DIFFERENCES VERIFICATION IN FIG. 15. Outline of research program. the method should allow the pilot some form of mobility—that is, the pilot should be allowed to make navigational decisions and act on those decisions. No feasible simulation technique was found which will adequately satisfy both requirements. It is pos- sible, however, to satisfy the requirements by using comple- mentary methodologies. For those research problems which demand fidelity of visual cues, a variety of motion-picture techniques can be used. In the technique now being implemented, wide-angle, color motion pictures are taken from a low-flying aircraft and back-projected onto a screen surrounding a simulated aircraft cockpit. Using a special Kinoptik lens, undistorted, high-re solution motion pic- tures can be taken of visual field 85° by 67°. It is also possible to obtain a 256° visual field by the use of three cameras (Figs. 16 and 17). The main limitation in the motion-picture methods is that the pilot is a passive observer in the simulated aircraft. It is pos- sible to give him various control tasks to perform, but these will not influence the visual field, although it is possible to pro- vide some visual compatibility with pitch, yaw, and speed con- trol. However, the technique has the advantage of being relatively inexpensive, and is well adapted to the study of visual-reference problems (variables affecting the detection and identification of checkpoints. Chart-interpretation problems are almost insepa- 161

FIG. 16. rably linked to the visual-reference problems and can be studied with this approach. Those weather conditions affecting visibility can be studied by this method, as well as the investigation of individual differences. For those problems in which visual-cue fidelity is not abso- lutely essential, but where it is mandatory that the pilot be allowed command of the movement of the aircraft, terrain-model methods can be applied. There presently exist various facilities that can be adapted to research on geographic orientation. One of these is located at North American Aviation's flight simulation laboratory in Columbus, Ohio. The facility consists of a terrain model over which a television camera moves. The camera is servoed into the controls of a simulated cockpit, and the output of the camera is projected on a screen on front of the cockpit. This device allows pilot mobility, but the visual cues are too 162

I" EFL f/1.8 PROJECTION LENS SCREEN ELEVATION FIG. 17. degraded for use on problems requiring visual-cue fidelity. How- ever, many of the research problems in the area of dead-reckon- ing procedures, preflight planning, instrument error, and wind conditions could be studied using such devices. The final step in the program must be the verification of the findings of laboratory studies through field studies. These studies would involve the use of real aircraft in the real world. The program is now in its second phase, in which the motion- picture technique is being used. The effort involves four tasks: the production of the motion-picture materials, the instrumenta- tion of the visual-flight simulator, the execution of a series of methodological studies designed to identify the most reliable per- formance measures and experimental procedures, and the execu- tion of the first series of experimental studies of the visual aspect of low-level navigation. REFERENCE McGrath, J. J. & Borden, G. J. Geographic orientation in aircraft pilots: a problem analysis. Los Angeles Human Factors Research, Inc. tech. Rep., 1963, No. 751-1. 163

DYNAMIC VISUAL DETECTION RECOGNITION Charles P. Greening Autonetics, North American Aviation, Inc. IMPORTANCE OF VISION FROM LOW-ALTITUDE AIRCRAFT In spite of the development of new sensor devices and the improve- ment of old ones, the unaided eye remains an important source of outside-world information in aircraft systems. Its small size, light weight, low power requirements, high reliability, and con- venient packaging are well known. Unfortunately, not as much is known as should be about its performance characteristics. Impact of New Requirements The defensive environment has forced aircraft to operate in the basically hostile regime of very low altitudes, and to do so in poor weather and/or at night, if possible. Flight operations at very low altitudes—200 (ft) and below—have increased the demands on the visual system by changing what used to be a quasi-static visual problem to one with complex dynamic properties. The subsequent sections of this paper describe: (a) a schema for relating those dynamic properties to other aspects of visual research, (b) some of the dynamic properties of low-altitude vision, and (c) some of Autonetics' data on dynamic target detec- tion and recognition performance. RELATION BETWEEN STATIC AND DYNAMIC PROPERTIES OF VISION The problem of developing good experimental data incorporating dynamic and static variables typical of the real visual world can 164

perhaps best be looked at with the aid of a qualitative three- dimensional diagram (Fig. 1). The three axes represent visual complexity, dynamic complexity, and degree of experimental control. It is necessary, somehow, to approach the rear upper right corner of the diagram. Number 1 on the diagram represents observations reported by airborne observers. The visual and dynamic properties of the real world are fully represented by definition. The introduction of experimental control into these observations, however, pre- sents stubborn problems. Among them are: (a) the difficulty of flying an aircraft repeatedly over precisely the same path, (b) the seasonal and diurnal changes in character of the foliage and other features of the world, (c) rapid changes in illumination and in atmospheric transmission, and (d) the difficulty of introducing systematic changes in size, color, location, or orientation with such targets as factories and highway bridges. In spite of these difficulties, partially controlled flight test programs are going forward at Autonetics and elsewhere. Some of the control problems described above can be eased by going to a high-fidelity terrain simulator. This simulation approach is represented by number 2 on the diagram. The visual character of the real world is almost entirely duplicated, if the job is carefully done. The dynamic properties of the real world can be correctly represented. Control of certain variables, such as illumination, vehicle position, and seasonal changes, can be achieved more readily than in flight testing. The systematic control of target and background properties such as masking, texture, and clutter, is still difficult, since there are no really appropriate descriptive metrics for them. Even very good simu- 1-FLIGHT TEST 2-TERRAIN SIMULATION 3- STATIC EXPERIMENTS 4-DYNAMIC EXPERIMENTS DYNAMIC COMPLEXITY- FIG. 1. Schema for dynamic low-altitude vision research. 165

lator data may differ from airborne data, e.g., recognition ranges, by a factor of two (Blackwell, Ohmart, & Harcum, 1959). Number 3 on the diagram represents the careful, static ex- periment typical of much good vision research. Control is maxi- mized, while visual complexity may vary over a wide range in these experiments from Landolt rings on a white background to highly textured representations of the real world. A few people have introduced some dynamic elements into this kind of work (Miller, 1958; Lippert, 1962; & Erickson, 1963), usually with relatively simple visual materials. Number 4 represents an attempt, just getting under way in Autonetic's laboratory, to start with visually simple, controlled, dynamic material, and gradually to increase the visual com- plexity. There are no data to report from this work yet. The laboratory is designed to preserve all the dynamic properties of low-altitude flight, as is a high-fidelity terrain simulator. It is anticipated that the controlled addition of visual complexity will permit separation of the effects of parameters which, in nature or terrain simulation, are usually confounded. DYNAMIC PROPERTIES OF THE LOW-ALTITUDE VISUAL FIELD Single-Point Geometry Unaccelerated flight past a point on the ground produces changes in the line-of-sight to that point, as shown in Fig. 2. The apparent angular position of a point on the ground changes relatively slowly when the range is large compared to the altitude. As the aircraft approaches the object, its apparent angular motion increases rapidly until it reaches the position of nearest approach and then it recedes in symmetrical fahsion. Fig. 3 (Greening & Sweeney, 1962) shows curves of angular rate versus time. Extended-Object Geometry When a collection of points comes under observation, the geome- try becomes more complex. All the characteristics of the static search, detection, and recognition problem exist at any one in- stant, but the quality of the picture also changes significantly with time. Some of the changes are described below. 1. Angular subtense. The angular subtense of any extended target normal to the line-of-sight is a/R, where "a" is a linear dimension of the target, and "R" the range to the target. For a 166

r t RAOIANS'SECONOS 1.5- L2- 11- LO- 8l2- 11- 0 VALUES OF L, LATERAL OISTANCE AT NEAREST APPROACH: L= 0 L= 1,000 FT L = 2,000 FT L = 6,000 FT L = 18 ,000 FT FIG. 2. Apparent angular motion of ground objects. t -t (SECONOS) But —— = sin Hence FIG. S. Angular rate as function of time. 167

rectangular element with dimensions a x b, the apparent area will be ab/R2 (Fig. 4). Thus, as the object is approached, its apparent linear dimensions increase as 1/R, while its apparent area increases as 1/R2. For a small horizontal surface, the lateral subtense is again approximated by a/R. But, the vertical subtense can be seen to involve the altitude, H. For small angles, the vertical subtense will be x/R = (H/R) = (b/R) = Hb/R2. Thus, a linear feature along the flight path will lengthen apparently as 1/R2, while lateral linear features are growing as 1/R. The apparent proportions of horizontal (or inclined) surfaces will thus be changing with time. HORIZONTAL OBJECTS FIG. 4. Subtense of distant objects. Following the same reasoning, the apparent solid angle sub- tended by a small horizontal surface will be approximated by (a/R) x (Hb/R2) = AH/R3, where A = a x b, the area of the hori- zontal surface. In a target complex made up of a horizontal area with projec- tions on it, e.g., buildings on flat ground, the total apparent angu- lar subtense of the horizontal elements will be increasing faster, 1/R3, with decreasing range than the vertical elements, 1/R2 (Fig. 5). Thus, at a distance, a village appears to be almost all buildings, fences, etc., while from close range (more oblique aspect) it seems to be mostly ground, roads, etc. This relationship holds also for objects too small to be re- solved individually, such as grass, pebbles, etc. The result is 168

-SUBTENSE (MILLIONTH5 OF STERAOIANS) HORIZONTAL 1 SUBTENSE ASSUME: ALTITUOE = 200 FT VERTICAL TARGET - 10 X 10 FT HORIZONTAL AREA (25 X 100 FT) 0 2 4 6 8 10 12 RANGE (1,000 FT) FIG. 5. Apparent size of horizontal and vertical surfaces. an inevitable change in visual texture and, usually, in apparent brightness and color as well, independent of atmospheric effects or visible details. 2. Apparent relative position. The apparent relationships among separated points in the visual field also undergo continu- ous significant changes when viewed from a low-altitude vehicle. For objects viewed as a pattern, this means that the aspect of the pattern varies with time. For more widely separated objects, some or all of which have significant vertical extent, observer motion at low altitude pro- duces the effect of intermittent, partial, or total eclipsing of one object by another. Such masking effects seem certain to have an important effect on airborne recognition performance, but data and descriptive metrics are lacking. All the geometric effects described above act in addition to, and probably interact with, the static visual variables such as contrast (brightness and color), shape, atmospheric attenuation, clutter in the visual field, etc. One brief analytical attempt has been made to combine these variables in a form usable for quasi- dynamic prediction. Using static data presented by Middleton (1952), Boynton (Boynton & Bush, 1958a; Boynton, Ellsworth. & Palmer, 1958b), the apparent contrast has been plotted as a func- tion of range, meteorological conditions, and target size (Fig. 6). 169

APPARENT CONTRAST (CR) 1,000-FT2 TARGET 10-MILE OAYLIGHT VISUAL RANGE MINIMUM CONTRAST V"FOR95, OETECTION \PROBABILITY 1,000 3,000 5,000 7,000 9,000 11,000 13,000 15,000 RANGE (YAROS) FIG. 6. Recognition range and apparent contrast. If one now assumes a target of 1,000 ft2, with a contrast (Co) of 0.5, one can visualize riding the 0.5 curve in toward the left as a function of one's motion toward it. When this curve crosses the 60 per cent recognition curve, it ought to be recognized. A family of these curves could be computed for different meteorological range, target size, and so on. But, it is probably not worth doing because the data would be obtained under condi- tions so different from low-altitude flight. Some of the airborne data has been checked against these curves without noticeable agreement. These data are presented after the flight test pro- grams have been described. EXPERIMENTAL RESULTS Simulation After an early analytical look at the low-altitude vision problem, one attempt at a motion-picture simulation was made, an outdoor parking area, natural lighting, and simple geometric objects (Snyder & Greening, 1963). In the experiment, target size and proportions, lateral offset at nearest approach, vegetative mask- ing, and ground speed were systematically varied. In the three- dimensional diagram presented earlier, this study corresponds to full dynamic properties, relatively simple visual properties, and modest control of variables. 170

The recognition-range results are shown in Fig. 7. Assuming a scale of 1 to 100, the results indicate a range of approximately one mile for an object the size of a large truck. This experiment left a good deal to be desired in terms of experiment control. The difficulty of controlling conditions led directly to the design of the Dynamic Vision Laboratory, recently activated at Autonetics. ou- 50- -] 40- - 30- - 20- 10- 0J 1-1/23 3/4 x 3 « 1 23 1-1-4 TARGETS (INCHES) FIG. 7. Mean range of correct recognition (simulated). Flight Tests The initial flight test of low-altitude visual performance was an attempt to introduce as much experimental control as possible into a real-world study. Four tactical targets using three dif- ferent configurations were deployed on a specified target area 5.2 miles in length. The target area terrain was relatively flat Southern California desert, spottily covered with Joshua trees, brush, and some grass. The target positions were all natural clearings in the target area. The targets were a yellow jeep, a yellow truck, a two-man tent, and a simulated two-man gun position. They were chosen so that they could be readily moved between aircraft passes, and yet had some tactical significance. A Beechcraft aircraft was equipped with a forward-looking 16-mm movie camera, a forward-looking television (TV) camera and monitor, and a 16-mm camera recording the TV. A total of 171

24 passes was made over the target area to permit counterbal- ancing target arrangements, direction of flight, location of ground track, and altitude. During each flight, an airborne visual ob- server and a TV observer searched for the four targets. Each was instructed to press a switch as soon as he recognized each target. In addition, the motion-picture films of the direct and televised forward view were used in the laboratory for additional data, with larger subject populations. Major results of the study are shown in Fig. 8 and Fig. 9, and described more fully in Snyder, Greening, and Calhoun (1964). PROPORTION OF TARGETS IDENTIFIED 0.5 r- 0.1 - HIGH (100 FT) TARGET TYPE ALTITUDE FIG. 8. Proportion of correct recognition, by altitude and by target. r- MEAN RECOGNITION RANGE (FEET) -i NOT SIGNIFICANTLY • / DIFFERENT P<0.05 700 600 500 400 300 200 100 0 1 NOT SIGNIFICANTLY DIFFERENT MEN TRUCK JEEP TENT TARGETS FIG. 9. Mean recognition range, by target. 172

In general, the results support other studies (Moler, 1962, Black- well et al., 1959; Thomas & Caro, 1962) which have shown that the probability of correctly recognizing small tactical targets from low-altitude aircraft is undesirably low. Typically, these probabilities range from 35 per cent for tank-size targets to 5 per cent for small, troop-size targets. Furthermore, the median range at which such targets are correctly recognized in these and other studies is typically on the order of 2,000 ft. The range data in the Autonetics study were all obtained from the film experiment. Problems in airborne data collection pre- vented comparison of these with direct visual recognition ranges. A second, more elaborate flight test program is now in prog- ress. This program is being conducted primarily as a multiple- sensor (visual, TV, radar, and infrared) comparison study. Only the visual data have been partly reduced, however, and they are the data of most interest to the reader. The targets were 29 cultural objects ranging in size from a highway cloverleaf to the Santa Monica pier. Obviously, the con- trol of target location was a luxury not possible in this series. Data where obtained, however, at three altitudes for all targets. Subjects were trained aerial observers, who were provided with briefing photos and map locations of each target. Because of the high cost of flight testing, the number of observations of each target under any condition is small. However, collapsed data pro- vide meaningful results when recognition range is plotted against altitude (Fig. 10), or is computed for representative targets TDK UK 50K P LU 40K Lj- 1 30K 2DK 15K HIK 5K 200 400 600 800 1000 1200 1.400 IjMO ALTITUOE (FEET) ABOVE GROUNO LEVEL FIG. 10. Data points and mean recognition ranges. 173

E 1. Menu Recognition Ranges for Selected Targets Target Range (ft) Suspended pipeline 10,100 Highway cloverleaf 17,800 Freeway intersection (harbor and San Diego) 21,400 Oil tank farm (Long Beach) 27,600 Santa Monica Pier 36,600 Power station 42,800 (Table 1). Probabilities of target recognition were high under most conditions in this study. No target was more than a few hundred feet off the flight path, however. The most effective way to get an idea of the visual world from this altitude regime is to view a section of the forward-looking film. The changing geometry can be clearly seen, and the targets should be readily detectable. CONCLUSION This paper has described some of the struggles at Autonetics to answer the simple question "What can a man see out of a low- flying aircraft?" One potential danger in this field would seem to be sheer exhaustion from attempting to explore all main effects and significant interactions among the numerous visual and dynamic variables. Consequently, an attempt has been made, probably prematurely, to link the flight data just obtained with f fO yi f*. »J O O o C3 C APPARENT CONTRAST (CM C0 = 4.0 (PIPELINE :> / \ /MINIMUM Cr FOR 60% / RECOGNITION / PROBABILITY 1,000-FT2 \ \ r TARGf SEC/C :T, 1.5 SEC 1BJECT, 10-MILE OROLOGICAL \ \ y METE co= i.o IX^ / RANG 1 E _EGENO: (BRIOGE) LINE RECOGNITION GE RECOGNITION "**• **.• 0 BRIO 1 _— — • •o- 10 20 30 40 RANGE (FEETX 1,000) 60 70 FIG 11. Selected flight test data points compared with static prediction. 174

previous static laboratory data. Selected experimental points have been plotted on the static curves described earlier (Fig. 11). The wide scattering of data points would seem to indicate that the researchers in Autonetics laboratory are still a consider- able way from predicting dynamic visual performance with a simple model based on static data. It is hoped that pushing for better control in the flight work and for better dynamics in the laboratory, will bring the far corner of the cube closer in the future. REFERENCES Blackwell, H. R., Ohmart, J. G., & Harcum, E. R. Field and simulator studies of air-to-ground visibility distances. In Ailene Morris & E. P. Howe (Eds.), Visual search techniques. Pub. No. 712. Washington: Nat. Acad. Sci., 1960. Boynton, R. M., & Bush, W. R. Laboratory studies pertaining to visual re- connaissance. Wright-Patter son AFB: WADC tech. Rep. D1958, No. 55-304, (Part II). (a) Boynton, R. M., Elworth, C., & Palmer, R. M. Laboratory studies pertain- ing to visual reconnaissance. Wright-Patterson AFB: WADC tech. Rep., 1958, No. 55-304 (Part HI), (b) Erickson, R. A. Visual search performance in a moving structured field. USN Ord. Test Station, 1963, No. IDP-1745. Greening, C. P., & Sweeney, J. S. Vision from low-flying aircraft. Suto- netics Lab. Rep., 1962, No. EM 1162-103. Lippert, S. Dynamic vision—the legibility of equally spaced alphanumeric symbols. Douglas Aircraft Corp. Engng. Paper, 1962, No. 1481. Middleton, W. E. K. Vision through the atmosphere. Toronto: Univer. of Toronto Press, 1952. Miller, J. W. Study of visual acuity during the ocular pursuit of moving test objects: II. effects of direction of movement, relative movement, and illumination. J. opt. Soc. Amer., 1958, 48, 803-808. Moler, C. G. Helicopter armament program: air-to-ground detection and identification. USA Ordn. Tech. Memo., 1962, No. 1-62. Snyder, H. L. & Greening, C. P. Visual performance in simulated low- altitude night. Autonetics Lab. Rep., 1963, No. EM 1163-123. Snyder, H. L., Greening, C. P., & Calhoun, R. L. An experimental compari- son of TV and direct vision for low altitude target recognition. Lab. Rep., 1964, No. T-46/3111-4. Thomas, F. H., & Caro, P. W., Jr. Training research on low-altitude visual aerial observation: a description of five field experiments. Washington: HumRRO Res. Memo., 1962, unnumbered. 175

OPERATIONAL PROBLEMS ASSOCIATED WITH LOW-ALTITUDE FLIGHT Robert W. Bailey U.S. Army Aeromedical Research Unit Fort Rucker In order to make any comments about the operational problems associated with low-altitude flight in Army aviation more mean- ingful it should first be explained what "nap-of-the-earth" can mean in terms of flight profile (Bell Helicopter Corp., n. d.). It should be remembered too, that in most cases Army aviators pilot, navigate, observe, and fire at targets with the aircraft armament, or direct the fire of supporting artillery. Such an operation is classified as a "complex-task." Nap-of-the-earth, however, does not always mean this type of profile. Army tactical doctrine defines nap-of-the-earth flying as follows: "Nap-of-the-earth flying is employed as a protection against enemy observation and weapons. It is a flight conducted in close proximity to the earth; normally below the height of surrounding trees, in stream beds, valleys, or any fold of the earth that affords protection from enemy observation and fire." In fairly even terrain this doctrine usually requires flying along stream beds in low, close proximity to the earth profile. In more hilly and mountainous terrain, however, flying behind a hill mask at an altitude of 1,000 feet (ft) could still be considered nap-of-the-earth, as it is defined. The altitude that will provide the required protection from enemy observation and weapons is selected. The problems involved have been identified by very little re- search and a great deal of subjective evaluation by aviators and those nonaviators who get a fearful amount of input as passengers. In 1957, at the Armed Forces-NRC Vision Committee meeting at Tufts University (Wulfeck & Taylor, 1957) the U.S. Air Force representative presented the problem of navigation at low altitude 176

as one of their most serious problems. Low altitude was then considered 200 ft, now that altitude is considered rather high in other than hilly or mountainous terrain. Even at a 200-ft altitude, visual navigation requires an accuracy of a fractional part of a mile. This is severely limited by two factors-apparent speed, and effective line-of-sight distance. If one considers that the apparent speed of an aircraft is inversely proportional to its height above the surface of the earth, then 100 knots * at 20 ft is equivalent to 500 knots at 100 ft, and 2,500 knots at 500 ft. At these low altitudes it becomes apparent that the helicopter must be regarded as an extremely high-speed aircraft. The second factor is that of the effective line-of-sight distance and the effective surface area within this line-of-sight distance. Extrapolation of the reasonably effective visual range at this altitude was made from some data included in a Marine Corps study (Marine Corps School, 1961) which worked out to be about 0.188 nautical miles, or 1,142 ft. Any distant point that is fixated can, therefore, be expected to pass beneath the aircraft in about 7 sec after it enters the effective visual range. This is the pilots view of the problem of navigation. Consider in addition to this that the aircraft instrumentation is not espe- cially designed nor human-engineered to aid the pilot in flying this type of profile (Wright & Pauley, 1964). One striking ex- ample of this problem is the sexagesimal clock in Army aircraft. This is the aviators' speedometer and odometer, but it requires mental calculation to convert elapsed time in minutes and seconds to miles or kilometers per hour. If you have just flown 1.7 km in 42 sec, how long is it going to take to complete the leg of 8.3 km? What is your present ground speed? On a new helicopter this clock is on the floor console. For the readers particularly interested in these factors as they influence low-altitude naviga- tion the following report is recommended: "Task Lowentry Sur- vey Reports" by R. H. Wright and W. P. Pauley, U.S. Army Aviation Human Research Unit, Fort Rucker, Alabama. The assumption that navigation is a real operational problem has been sustained by Dr. McGrath's paper presented in these Proceedings (McGrath, 1963). His data revealed that aviators who became geographically lost will eventually fly into the ground, or abandon their aircraft unless they are able to re-establish their geographical position. This disorientation is not system- atically related to distance, however, so that the shorter radius 1. Knot = nautical mile (6,076. 1033 ft)/hr. 177

of operation in Army aviation (1-100 miles) is just as sensitive to this problem as are the longer missions of other services. There are other problems associated with flying nap-of-the- earth. 1. There is a definite decrease in security and a resultant increase in stress on the pilot due to his relative air-ground position. In the fixed-wing aviator this may start to occur at altitudes as low as 300 ft and at air speed of only 70-80 knots. However, this altitude and air speed is comfortable to the rotary-wing aviator. 2. The complex task of flying low profiles is not the same for helicopters as it is for fixed-wing pilots. This is due to the lag between control input and response in the helicopter, which is considerably longer than in fixed-wing aircraft. Also, the heli- copter is an inherently unstable platform that requires constant active control employing both hands and both feet. 3. At very low altitudes, e.g., 30 ft, on flat terrain the visual streaming effects have been reported to produce nausea in pilots flying at 250 knots.2 The Army surveillance aircraft, OV-1, is capable of flying at this speed, and new experimental helicopters are rapidly approaching the 200-knot/hr capability. There are two studies that have been done by the Defense Research Medical Laboratories of Canada (Lewis, 1961-1962), during extended low-altitude flight, which are pertinent to the human engineering deficit and the problem of navigation. In these studies, Canadian Army pilots were required to navigate accu- rately over unfamiliar terrain during flights flown nap-of-the- earth and lasting approximately two hours. Data were obtained about navigation capability, "head-down" time in the cockpit, number of times the pilots flew into wires or cables, and pilot errors such as forgetting to switch fuel tanks because they were so engrossed with the overloaded situation of navigation com- bined with low-altitude flying. In low-altitude flight such an error could be a fatal omission, but was avoided in these cases only because the experimenter was a passenger and either turned the switch for the pilots, or reminded them at the last possible moment. The same delayed interference was employed to pre- vent the pilots from flying into wires. Mr. Lewis, author of these studies, has made available a documentary film taken during one of these experiments in an 2. R. Wright, USA Aviation Hum. Res. Unit, Ft. Rucker. Personal com- munication, October, 1963. 178

L-19 fixed-wing aircraft, a standard light observation aircraft used by both Canada and the United States. The film shows that a "jury-rigged" map roller was required to overcome the human engineering lack in this aircraft. To the stress of low-altitude flight was added the burden of navigation. Fixation times on the roller map had a mode of 1.5 sec or less. Aircraft altitude was below 75 ft 90 per cent of the time. The turbulence often present on summer days at low levels can be noted. Observers or pas- sengers seldom endure more than 20 minutes of such turbulence without nausea. The major sensory input for such a complex task of flying is certainly vision. It is hoped that this brief and far from com- plete presentation about some of the operational problems in low-altitude flight has served to stimulate interest and provide insight into the problem. REFERENCES Bell Helicopter Corp. The Army and the H-13 Sioux on the warpath. (Film) Author, w.d. Lewis, R. E. F. Pilot performance during low speed, low level naviga- tion. Toronto: Defense Res. Bd of Canada DRML Rep., 1961, No. 248-1. Lewis, R. E. F. Pilot performance during low speed, low level naviga- tion. Toronto: Defense Res. Bd of Canada DRML Rep., 1962, No. 248-2. McGrath, J. J. A study of geographic orientation in aircraft pilots. Los Angeles: Hum. Factors Res. Inc. tech. Rep., 1963, No. 751-1. Marine Corps School. Marine Corps landing force development activities. Quantico: Develpm. Bull., 1961, No. 2-61. Wright, R. H., & Pauley, W. P. Lowentry 1 Survey Report. Fort Rucker: U.S.A. Aviation Hum. Res. Unit, 1964 unnumbered. Wulfeck, J. W., & Taylor, J. H. (Eds.) Form discrimination as related to military problems. Washington: Nat. Acad. Sci., 1957, Pub. No. 561. " " 179

SOME OPERATIONAL ASPECTS OF VISUAL PROBLEMS IN LOW-FLYING, HIGH-SPEED AIRCRAFT 1 Robert L. Jones and James S. Joska Air Proving Ground Center Eglin Air Force Base Penetration of enemy defenses and capability of survival in the face of current sophisticated defense systems have generated a need for low-altitude flight. Missions into enemy territory vary, however, and to understand the various aspects of visual prob- lems associated with low-altitude flight, it is necessary to deline- ate the types of missions involved in order to present specific problems. Low-altitude profiles for nuclear and non-nuclear warfare vary as do the low-altitude profiles for close-support and interdiction missions. Each has its own peculiar set of prob- lems. This paper considers the inherent problems contained in the close-support and interdiction type missions, noting that other areas remain, including those of air superiority, armed reconnaissance, and, of course, nuclear deliveries. Low-altitude flight is generally considered to involve flight 1. This paper is based on Projects 9069Z, 5967Z2, and 0501T1 conducted at the Air Proving Ground Center, Air Force Systems Command. The re- sults of the first of these projects were documented in PGN Document 64- 1, "Human Factors Aspects of Low-Altitude Flight: A Sample of Fighter Pilot Attitudes and Altitude Estimates," dated February 1964, prepared by Robert L. Jones of the Deputy for Effectiveness Test in collaboration with Jefferson F. Lindsey of the former Deputy for Bioastronautics, APGC. The findings of the second project were reported in PGT Document 63-1, "Effect of Aircraft Speed on Low-Altitude Acquisition of Ground Targets," dated December 1963, prepared by Major James S. Joska of the Deputy for Effectiveness Test, APGC. The results of the last project, which was a follow-on of Project 5967Z2, will be published by APGC in May 1964. 2. Now with Crew Systems Division, Manned Spacecraft Center, NASA, Houston, Texas. 180

at an altitude of 500 ft or less. High-speed flight at these alti- tudes produces numerous problems. The pilot is confronted with the increased probability of disorientation, difficulty in recog- nition of significant checkpoints on a critical flight path, and, of course, the constant avoidance of collision with the terrain. It can be seen, then, that flying at low altitudes involves more than just navigation. The Deputy for Effectiveness Test, Air Proving Ground Cen- ter (Air Force Systems Command), in conjunction with the Tac- tical Air Warfare Center (Tactical Air Command), both located at Eglin Air Force Base, is currently focusing attention on prob- lems encountered in close-support and interdiction missions. Each of these missions, as they are considered here, involves problems in low-altitude flight, namely, navigation to the target area, search for the target, target acquisition, 3 target recognition, tactical maneuvering, weapons delivery, and escape (see Fig. 1). The distances at which acquisition and recognition occur must be considered for herein lies the limitation for employment of FIG. 1. Phases of target acquisition, rec- ognition, and destruction. 3. In this paper, target acquisition is considered as that point at which detection of the target occurs. 181

FIG. 2. Critical target acquisition and recognition distances and critical angle- off for executing tactical maneuver for ordnance delivery. available weapons through tactical maneuvering (Fig. 2). For example, rocketry and strafing are severely limited from a high- performance aircraft flying at extremely low altitudes. Other types of munitions must be employed, dependent, obviously, on the type of target under attack. If, in approaching the target lo- cation, the pilot is several degrees to one side of his target he must maneuver his aircraft, in accordance with an accepted tactic, to line up on the target in order to deliver his weapon. Such a maneuver is time-consuming and can involved severe physical stresses on both the pilot and the aircraft during flight. Also, psychological stress for the pilot might very well be in- creased as a function of prolonged exposure to enemy defensive ground fire during this maneuver. In a situation emphasizing the use of a high-performance air- craft in the missions under consideration where ground-to-air defensive weapon systems make the capacity to survive a critical factor, there arises a problem of a compromise of survival in order to achieve effectiveness. The Deputy for Effectiveness Test has begun an investigation of factors involved in achieving a "first-pass acquisition, recognition, and fire" situation, where 182

the pilot might acquire, recognize, and destroy a target on a single pass. Information was needed to determine the probability of achieving this event, for attaining such proficiency appears to be significant, especially in light of the sophisticated defense systems anticipated. Recently, interviews with 15 Tactical Air Command (TAG) flighter pilots completing live-fire training passes on targets which were well hidden among trees revealed that first-pass acquisition, recognition, and fire was reported as occurring only approximately one-third of the time. Further, the flight leaders reported achieving this event significantly more often than the Number 2, 3, or 4 pilots in the flight. Perhaps this was due to the superior skill and more extensive experience of the flight leaders. There is also the factor that the flight leader can devote his full attention to the acquisition-recognition-firing task, while the remaining men in the flight have to be concerned with flight integrity, i.e., position, spacing, etc. The first-pass acquisition, recognition, and fire capability seems to be desirable, but elusive. Data on low-altitude flight directly pertinent to tactical opera- tions gathered from field tests in which high-performance air- craft and qualified line fighter pilots were utilized are extremely rare. Regulations of the Federal Aviation Agency (FAA) severely restrict flying at an altitude of 500 ft or lower, except for certain approved routes laid out for special training missions. Since pilots are unable to acquire extensive high-speed, low-altitude flight experience, and will certainly not admit to "buzzing" epi- sodes, data are unavailable. Considerable differences of opinion concerning pilot capability to perform low-altitude flight are seen to exist, further compli- cating the lack of objective data in the area. To obtain some in- sight into "how low is low," and how low pilots feel they can fly, a sample of 58 highly qualified U.S. Air Force TAG fighter pilots were asked to estimate the lowest altitude they felt they could comfortably maintain for certain specified conditions. The rela- tionships among speed, flight duration, flight conditions (favorable versus unfavorable), and altitude estimates, as well as interac- tions among these factors, were investigated. In preparing the altitude estimate data for analysis, two sepa- rate classes of data were established: (a) data on estimates made for reciprocating-engine aircraft, and (b) data on estimates made for jet aircraft. These were then broken down further into data based on time, which made possible an analysis of variance for estimates pertaining to flight duration—10 min, 1 hr, and 1 to 2 183

hr. To evaluate the human-factors aspects of the estimates, the pilots were grouped according to anxiety level, total flying hours, and total jet time. Anxiety levels, using scores based on the In- stitute for Personality Testing (IPAT) Anxiety scale were: Low, 5-14; Medium, 18-23; High, 23-37. Total flying hours were: Group 1, 0-999 hr; Group 2, 1,000-1,999 hr; Group 3, 2,000-2,999 hr; and Group 4, 3,000 hr or more. Total jet time was: Group 1, 0-1,000 hr; Group 2, 1,001-2,000 hr; and Group 3, 2,000 hr or FIG. 3. Means for altitude estimates for reciprocating-engine and jet aircraft: total pilot group (N = 58). more. The means for the altitude estimates for both reciprocat- ing-engine and jet aircraft for the total subject group are shown in Fig. 3. The means for the estimates made by the pilots in each of the human-factors groupings for each type aircraft and for the three flight duration periods are shown in Fig. 4 through Fig. 12. The relationships between anxiety level and the estimates made by the pilots are extremely interesting, since subjects of high anxiety made significantly higher altitude estimates, with unfavorable conditions and longer flight durations interacting with anxiety level. Since pilots reported that low-altitude flight tends to be stressful (Jones & Lindsey, 1964), and since stress 184

FIG. 4. Means for altitude estimates for reciprocating-engine and jet aircraft: 10-min flight duration period—anxiety grouping. FIG. 5. Means for altitude estimates for reciprocating-engine and jet aircraft: 1-hr flight duration period—anxiety grouping. 185

Gwen SpMdlKmm) FIG. 6. Means for altitude estimates for reciprocating-engine and jet aircraft: 2- to 3-hr flight duration period-anxiety grouping. FIG. 7. Means for altitude estimates for reciprocating-engine and jet aircraft: 10-min flight duration period—total flying hours grouping. 186

' .7 FIG. 8. Means for altitude estimates for reciprocating-engine and jet aircraft: 1-hr flight duration period-total flying hours grouping. FIG. 9. Means for altitude estimates for reciprocating-engine and jet aircraft: 2- to 3-hr flight duration period—total flying hours grouping. 187

UnUv«bl. FIG. 10. Mean for altitude estimates for jet aircraft: 10-min flight duration period—total jet time grouping. , y- *00 500 Given Speed (Knoli) FIG. 11. Mean for altitude estimates for jet aircraft: 1-hr flight duration period—total jet time grouping. 188

«» < I *" =fl± -H-ffl-fHf J.f Ai« rrr til i £H=F SS -f-H- FIG. 12. Mean for altitude estimates for jet aircraft: 2-hr flight duration period— total jet time grouping. tends to increase variance in performance, these findings are quite significant, for it might be expected that pilots of high anxiety would encounter greater probability of pilot error. The results certainly seem to warrant further investigation. In the total flying hour groupings, consistent trends demon- strating that pilots of greater experience (as evidenced by higher total flying hours) give lower altitude estimates were not present, and differences were not consistently significant. Therefore, it would appear that total flying hours may not be a significant cri- terion in selecting pilots to perform low-altitude flight. However, in two of the three total jet time groupings, results were in the expected direction, and subjects with the greatest total jet time produced significantly lower estimates. Perhaps, then, it is an important variable to consider. These data are far from conclusive, and it would certainly appear that close attention to the selection of pilots for the per- formance of critical low- altitude flight missions is warranted. Further research in this area is necessary if adequate under- standing of the problem is to be gained. 189

While these subjective data have much to offer in an approach to understanding and evaluating operational aspects of visual problems in low-altitude flight, field test data are absolutely necessary to improve simulation techniques, to evolve tactical concepts and doctrines involving low-altitude flight, and to improve weapon systems design. As stated earlier in this paper, data relating to the distance at which typical ground targets might be acquired and recognized during high-speed, low-altitude flight are not adequate. In fact, very little data obtained from physical testing are available. In order to approach this significant gap, a test was conducted at Eglin Air Force Base to determine the effect of aircraft speed on low-altitude acquisition of ground targets (Joska, 1963). Eleven pilots flew 44 acquisition passes against a typical ground target which was placed in a realistic setting. The F-100 aircraft was used with 500 ft as the test altitude, and acquisition distances were obtained for speeds of 250, 350, 450, and 550 knots. The data obtained are shown in Fig. 13. Since the sample was too small to establish stable means, a statistical test was performed to determine differences among target acquisition distances for the four speeds used during physical testing. A non-parametric test, known as the rank-sum test, was employed. Significant differences between the 250-550, and the 350-550 knot speeds were found to exist (see Table 1). To evaluate further the acquisition phenomena, a chi-square test was performed to determine the probability of target acqui- sition for each of the four speeds. Significant differences were again found, demonstrating less probability of target acquisition at the 550-knot speed (see Table 2). This test effort was considered to be a preliminary effort, or pilot study, and another test was performed under a separate project (APGC Project 050IT 1) using the F-105 aircraft flying at speeds of 350, 550, and 700 knots, again at an altitude of 500 ft. Targets consisted of three military-type vehicles, placed in line, perpendicular to the flight path. A total of 27 missions was flown, including single passes at each of three target groups per mission, or a total of 81 target passes. The results of this test were concerned with the relationship between airspeed and target acquisition distance and, as will be covered later, run number and target acquisition distance. Sec- ondary radar data plots were used as a source of data for the test, with target acquisition distances derived therefrom accu- rate to within +200 ft. The data were plotted in a chart for each 190

1000 4000 0 1000 2000 3000 4000 Acquisition OisMnce (Yards) FIG. 13. Line graphs showing distribution of acquisition distances for each of the briefed speeds: (A) 250 KTAS, (B) 350 KTAS, (C) 450 KTAS, (D) 550 KTAS. of the three speeds with each acquisition occurrence being plotted to the nearest 1,000 ft. These data are included in Fig. 14. The over-all appearance of the data display did not lead to any strong feeling as to the nature of the underlying frequency distributions. Therefore, means and standard deviations were calculated for each speed and the usual x^ "goodness of fit" test was used to test for normality. The \% test indicated no reason for rejection of the hypothesis that the acquisition distances were normally distributed. Additionally, the medians of the distance distribu- tions for each speed were determined, together with the grand median distance for all target passes. An analysis of variance was accomplished as if the test were a one-third replicate of a 9-3/3x3, four-factor experiment. Be- cause of military necessity, one pilot was unable to complete the three missions required and, hence, the number of levels of the 191

TABLE 1. Summary of Rank-Sum Test Results. Speed Versus Target Acquisition Distance.3 Test Speeds Sample No. Compared Sizes Results 1 250/350 KTAS0 7 Accept— no difference 10 due to speed 2 350/450 KTAS 9 Reject— a difference 7 due to speed 3 450/550 KTAS 6 Accept— no difference 5 due to speed 4 250/450 KTAS 5 Accept—no difference 6 due to speed 5 250/550 KTAS 7 Reject—a difference 7 due to speed 6 350/550 KTAS 9 Reject— a difference 6 due to speed 5% level of significance. Probability less than 5% Knots true air speed TABLE 2. Summary of Chi-Square Tests. Speed Versus Target Acquisition Probability.* Test Speeds Chi-Square No. compared Calculated From table** Results 1 All 9.755 7.810 Reject hypothesis- probabilities differ between speeds 2 250/350 KTAS 0.414 3.841 Accept— no difference 3 350/450 KTAS 0.023 3.841 Accept—no difference 4 450/550 KTAS 1.467 3.841 Accept— no difference 5 250/550 KTAS 6.828 3.841 Reject— probabilities differ between speeds 6 250/450 KTAS 0.053 3.841 Accept—no difference 7 350/550 KTAS 5.166 3.841 Reject—probabilities differ between speeds *5% level of significance. **Necessary for significance at or beyond the 0.05 level. 192

! G'ood 1 1 Medinn Mvdian g 1 X' X 1 x X! 1 Xi X K X x X X XX X X • X X X X X|X X x X 1 I 1 cdion J 'I ' 1 1 Jj X X X X X 1 1 • x x1 X x X X X X X X X X X X X x i X 2 1 ' ] l 1 * X xlx I X X X 1 X X X X x X x|x x I X X X X X X x Tvf*( AcqumlHHi DnUnc* If FIG 14. Frequency of occurrence of acquisition dis- tances for each of test speeds. first factor was reduced to eight. Additionally, this caused a certain degradation of results by an upset in the balance in blocks. Following necessary adjustments, it was determined that the only second-order interactions which were significant were the pilots with targets and pilots with trials. Finally, the analysis of vari- ance in Table 3 shows that speed was a significant factor in tar- get acquisition distance, and also that the number of trials by a particular pilot produced a significant difference in acquisition distances. The usual "studentized" range technique was used to determine possible groupings with mean acquisition distances calculated versus airspeed only. It was found that the mean acquisition dis- tances on the supersonic (700 knots) runs were significantly lower than the means for the subsonic runs, and that no significant dif- ference existed between the mean acquisition distances for the subsonic runs. Due to the small sample size obtained in this test and the magnitude of the standard deviations in the previous para- metric analysis, it was felt that a non-parametric analysis might produce a contradiction to the findings. Therefore, two non- parametric analyses were made which strongly supported the previous findings, thus giving additional assurance to the results. Fig. 15 illustrates the frequency of target acquisition distance occurrences for each run. This display alone leads one to believe that there is a significant learning factor involved between the first and second runs. The usual x2 "goodness of fit" test was used to test for the normality of the distributions. The results obtained show that the frequencies were not significantly differ- ent. The data sample was too small to allow an extrapolation within any reasonable degree of accuracy to compensate for the 193

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l i i 1 Gfond X g 8 X X X X X X X X X X X X X X X 1 2 g 1 1 1 Six 1 X SIS X X X X X X Ntt X X 1 X X X X X X X X X X X X X X X X X X X X X XX 34 32 30 75 26 24 22 20 IB 6 u U 10 B 6 4 2 * Acquililjon Diltonce (fix l000) Lin* FIG. 15. Frequency of occurrence of acquisition dis- tances for each run. apparent learning. Although it was known that the variance due to run number could affect the rest of the data, it would have been unreasonable to have attempted to make any compensations in the analysis before further test results were obtained. The fact in question is not so much that there was learning, but rather the degree of learning and the point at which the learning stabi- lizes. It is felt that after the second set of target passes by a particular pilot, his learning reaches a plateau. After additional testing has been accomplished, an attempt will be made to sub- stantiate this theory. Although the results of this test were obtained from a small sample size, there was strong support for the fact that target acquisition was affected significantly by the speed of the aircraft. In fact, the distance from the aircraft to the target at acquisition was decidedly less for air speeds in the supersonic region. It is felt that this distance was less to the extent that it put the pilot beyond the critical point in reaction time at which he could make the required tactical corrections for delivery of ordnance on the target. In light of these factors, another test is presently being con- ducted at the Air Proving Ground Center to evaluate training techniques designed to improve the perceptual efficiency of pilots and thus improve their capability for target acquisition and recognition. These techniques involve use of linearly programmed photo- graphs (ranging from low stimulus ambiguity to high stimulus ambiguity) of typical tactical targets which will be presented on a tachistiscopic teaching machine, allowing stimulus presenta- tion speeds of 1 sec, 1/2 sec, 1/10 sec, and 1/20 sec. The target 195

series consists of 18 targets, such as tanks, missiles, and anti- aircraft guns. Two film sequences comprise the total film pack- age, with the first film serving as the learning film. In the learning film, 14 views of each target, ranging from high-contrast photographs to low-contrast photographs, are presented in both slow and rapid order. The second film consists of an "eyeball training phase" in which 324 photographs of the 18 targets are presented to the subjects in random order in the high-speed mode only. Two groups of TAG line fighter pilots make up the sample. There are 20 pilots in each group, with one group re- ceiving conventional recognition training, as currently used in the field, and the second group receiving the special training outlined above. After completion of the training phase, both groups will be tested on 1-sec presentations of 72 views of the 18 targets. Following this, the pilots in each group will make target acquisition-recognition passes on four single targets placed on the range, perpendicular to the flight path. These passes will be flown at an airspeed of 550 knots at a 500-ft altitude. The two groups will be compared in regard to accu- rate target identification, distance at target acquisition, distance at target recognition, time lag between target acquisition and rec- ognition, and recall of details of the mission at time of debriefing. Such a technique appears to have a great deal to offer, not only in basic and specific programs of target recognition train- ing, but also in presenting to pilots, in a highly effective manner, other types of information such as foreign technical material, technical order data, low-level navigational routes with photo- graphs of checkpoints, and new reconnaissance data. All these data could be made available to the combat pilot and presented on a teaching machine for maximum effectiveness. Further, teaching machines are small and reliable, possessing great versatility, and film strips can be made up in a matter of days, hence, giving a reasonable reaction time for both large- and small-scale missions. SUMMATION The effort of the Deputy for Effectiveness Test in the area of low-altitude flight testing has been, to date, one of investigating various aspects of target acquisition and recognition, including evaluation of the techniques designed to improve the perceptual efficiency of pilots, and thus improve their capability for target 196

acquisition and recognition. Further tests are being established to evaluate target acquisition and recognition at various altitudes and speeds using fixed and mobile targets of varying contrasts. Future test efforts will involve search, acquisition, and recogni- tion of targets with live ordnance delivered against them. It is expected that these tests will be accomplished in 1964. While it is obvious that this total effort encompasses but a few aspects of the over-all low-altitude, high-speed flight prob- lem, the basic groundwork for solution of the problem is being carried out. It must be remembered that this effort was born of an operational need by a using command. This need must be satisfied in order to provide the necessary assistance to com- manders in the field, who are faced with the complex decisions of warfare, and who must have facts at their disposal to make their day-to-day "trade-off" between survival and effectiveness. REFERENCES Jones, R. L., & Lindsey, J. F. Human factors aspects of low-altitude flight: a sample of fighter pilot attitudes and altitude estimates. Eglin AFB: Air Prov. Ground Centr Doc., 1964, No. PGN 64-1 (APGC Proj. 9069Z). Joska, J. S. The effect of aircraft speed on low-altitude acquisition of ground targets. Eglin AFB: Air Prov. Ground Centr Doc., 1963, No. PGT 63-1. (APGC Proj. 5967Z2) 197

*- .„

"I. —

Vision Research: Flying and Space Travel; Proceedings of Spring Meeting, 1964. Edited by Milton a. Whitcomb and William Benson Get This Book
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Vision Research: Flying and Space Travel is a record of the proceedings of the Committee on Vision meeting in 1964. The papers presented at the meeting concerned visual problems related to low altitude, high-speed flight, space travel, and incapacitating effects on pilots resulting from inadvertent viewing of a nuclear detonation.

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