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OCR for page 32
32
Development of a Tool to Analyze Limitations
Airfield Separations
The methodology developed in this study has some limita-
An analysis process for each type of airfield separation is tions. Risk of collision between two aircraft, or an aircraft and
presented in Appendix A. The procedures are simple to use, an object, estimated with this methodology is applicable only
and the instructions include practical examples to help to straight parallel segments of taxiways and taxilanes.
the user. Although the lateral deviation data in taxiing operations
The methodology serves as a screening tool to support used to develop the risk plots were measured only for the
MOS requests involving airfield separations when the stan- B-747 aircraft, it is assumed that smaller aircraft have lateral de-
dards cannot be met. The process helps to quantify the risk viation distributions that have smaller ranges. Thus, the model
levels for non-standard conditions and, based on criteria rec- can be considered conservative when applied to smaller air-
ommended in this report, in agreement with the FAA risk craft. However, the taxiway deviation models used in this study
matrix, it is possible to evaluate the feasibility of approval of were developed from lateral deviation data collected on taxi-
an MOS request (FAA, 2010). ways with centerline lights. Therefore, the conspicuity of the
Different procedures are provided depending on the type taxiway/taxilane centerline is an added risk mitigation measure
of airfield separation. It is possible to analyze separations in- that should be used when justifying an MOS request.
volving runways, taxiways, taxilanes, and objects. A specific The FAA/ICAO CRM during missed approach was devel-
approach was used for each type of separation. To facilitate oped based on data for two- and three-engine jet airplanes. The
the application of the methodology, risk plots are presented veer-off models developed under this study are based on data
for each ADG, and when the analysis involves specific aircraft, from veer-off accident/incident reports taken from several
risk plots based on wingtip clearance are provided. countries and for aircraft with MTOW larger than 5,600 lb.
The collision risk during the approach phase of landing is
modeled for missed approach during instrument approaches
Recommended Risk Criteria for Taxiway under Cat I and II. This is assumed to be the highest risk con-
and Taxilane Separations dition, and the phase when the pilot is under visual condi-
tions is not modeled in the risk curves presented.
An extensive survey of historical taxiway and taxilane inci-
CRM risk is estimated for an aircraft located on the center-
dents helped assess the major factors involved in these events.
line of a parallel taxiway. The taxiing aircraft is of the same
Due to the slow speeds of aircraft on taxiways and taxilanes
ADG as the approaching aircraft, and the maximum tail
as compared to aircraft speeds on runway operations, even
height for the ADG is taken to characterize the obstacle lo-
under adverse weather conditions or slippery pavements, the cated in the taxiway. The same plots may be used to assess
pilot was able to stop the aircraft as soon as it departed the risks associated with other types of obstacles at a certain dis-
paved surface of the taxiway. Further, historical taxiway col- tance from the runway centerline; however, such obstacles
lision events were not related to taxiway deviations. In almost must be lower than the maximum tail height of the ADG used
every accident/incident, the collision occurred because there to develop the charts.
was another aircraft or movable object inside the OFA of the
taxiing aircraft. Recommendations for Future Work
One major conclusion is that the existing standards pro-
vide an excellent level of safety and that the risk is lower than Effort to Collect Taxiway/Taxilane
one accident in 1 billion operations. Even when another air- Deviation Data
craft or object was in the path, resulting in a collision, there As described in previous sections of this report, many of
has never been a serious injury associated with the accidents, the separation standards were developed during World
and the damages have been limited mostly to the wingtip of War II and were based on engineering judgment. These
the aircraft. standards have helped maintain very high levels of safety, as
Based on the available evidence, the worst credible conse- evidenced by the fact that there is no history of collisions
quence for a taxiway or taxilane according to the FAA risk between two aircraft taxiing in parallel routes.
matrix is major damage to aircraft and/or minor injury to With the increase in traffic volume and the need to increase
passengers/workers, major unplanned disruption to airport airport capacity, many airports are restricted in their ability
operations, or serious incident (FAA, 2010). For major con- to increase existing airfield separations to introduce opera-
sequences, the maximum acceptable level of likelihood is tion of larger aircraft. Although the FAA permits MOS based
"remote." In this case, a remote event is expected to occur on formulas developed for this purpose, the formulas were
once every year or 2.5 million departures, whichever occurs developed based on engineering judgment, rather than using
sooner. a probability approach.
OCR for page 33
33
Recent FAA studies on aircraft deviation for large aircraft Cat I and II. The CRM model was based on the limited data
have demonstrated the feasibility of collecting data to develop available at the time it was developed. Aircraft technology and
risk models. However, these studies have focused on large air- navigational aids have improved significantly since then. As
craft on taxiway segments with centerline lights. There is a need it is expected that airport capacity will need to increase two-
to collect additional data for various categories of aircraft, for or threefold in the near future, it is necessary to develop a
both taxiway and taxilane segments, under various environ- more rational approach to more accurately assess the level of
mental conditions, with and without conspicuous centerline safety. Many airports still rely on visual and non-precision
markings, and with and without centerline lights. approaches, and for these categories, that analysis can be
Such studies should not be undertaken to modify the cur- made only by using Part 77 imaginary surfaces obstruction
rent standards, but they can support MOS processes when the evaluation to obtain a very basic assessment of risk.
evaluation of shorter-than-standard distances is necessary. A risk-based model for the assessment of visual segment or
non-precision approaches would benefit many airports in the
United States and abroad, particularly for the evaluation of
Effort to Collect Aircraft Deviation Data
airfield areas. Therefore, studies that address risk assessment
during Landing and Takeoff Operations
for aircraft operations associated with movable or fixed ob-
The development of risk plots for the airborne phase of jects within or in the vicinity of airports would greatly bene-
landing used the FAA/ICAO CRM for instrument approach fit the aviation industry.
