used by the airline's engine overhaul facility. As a result, a fatigue crack originating from a previously undetected metallurgical defect was not detected. The subsequent catastrophic disintegration of the part produced debris with a pattern of distribution and with energy levels that exceeded the level of protection provided by design features of the hydraulic systems that operated the aircraft's flight controls.

In this example, one link in the chain was singled out as being more significant than the others, which included the processes used to produce the basic material for the rotating part, numerous inspections designed to detect the defect before it became a crack, and the susceptibility of the aircraft design to damage by the distribution of debris in this particular failure. The committee believes that a safety management program should have an inclusive view of what constitutes a significant cause to ensure that corrective action addresses multiple cause factors and provides multiple assurances that a similar accident or incident will not occur in the future.

For the purposes of analyzing the most common causes of accidents, the committee reviewed official accident reports and various summaries of those reports. Figures 3-3 and 3-4 show the primary cause factors cited in official reports of accidents resulting in the loss of aircraft. Data from both the U.S. and worldwide fleets of commercial jet airplanes are shown for two periods: since the beginning of the "jet age" (1959 to 1996) and during the last 10 years (1987 to 1996) (Boeing, 1997).

Figure 3-3 shows that there were 50 hull loss accidents worldwide between 1959 and 1996 in which the airplane was a primary cause factor. Figure 3-4 shows that 15 of these accidents took place in the United States. For the 50 accidents worldwide, Figure 3-5 shows the breakdown by aircraft system.

Although data on primary cause factors are readily

Front Matter (R1-R12)

Executive Summary (1-6)

1 Introduction (7-9)

2 Role of the Aircraft Certification Service (AIR) (10-21)

3 Causes of Incidents and Accidents (22-28)

4 Recommended Safety Management Process (29-39)

5 Human Factors (40-43)

6 Barriers (44-49)

7 Small Airplanes and Rotorcraft (50-54)

Appendix A: List of Findings and Recommendations (55-59)

Appendix B: Biographical Sketches of Committee Members (60-62)

Appendix C: Participants in Committee Meetings (63-64)

Appendix D: Data Requirements (65-68)

Appendix E: Probability and Reliability Analysis (69-72)

Appendix F: Sample Legislative Amendment for Approved Design Organizations (73-73)

Acronyms (74-74)