Risk Assessment Method to Support Modification of Airfield Separation Standards (2011)

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ACRP study are based on data from veer-off accident/incident reports taken from several countries and for aircraft with max- imum takeoff weight (MTOW) larger than 5,600 lb. The collision risk during the approach phase of landing is modeled for missed approach during instrument approaches under Cat I and II. This is assumed to be the highest risk con- dition, and the phase when the pilot is under visual condi- tions is not modeled in the risk curves presented. CRM risk is estimated for an aircraft located on the cen- terline of a parallel taxiway. The taxiing aircraft is of the same ADG as the approaching aircraft, and the maximum tail height for the ADG is taken to characterize the obstacle located in the taxiway. The same plots may be used to assess risks associ- ated with other types of obstacles at a certain distance from the runway centerline; however, such obstacles must be lower than the maximum tail height of the ADG used to develop the charts. Risk Criteria The suggested risk criteria to use with this methodology are those used by the FAA and represented by the risk matrix shown in Figure A-1 (FAA, 2010). A risk classification (high, medium, or low) is provided based on the combination of severity and likelihood. Severity is the measure of how bad the results of an event are predicted to be and is defined as the worst credible conse- quence that may take place for risk associated with a given hazard. Likelihood should be considered only after determin- ing severity, and at the same time, likelihood should not be considered when determining severity. Definitions for each level of severity and consequence are presented in Tables A-3 and A-4. Two cases can serve as examples: (1) risk of collision between an aircraft landing and an aircraft located in a parallel taxiway and (2) risk of wingtip collision between aircraft taxiing in parallel taxiways. The first step is to determine the worst cred- ible consequence for each of these events. The worst credible consequence for runway veer-offs in most cases is hull loss and multiple fatalities, which is classified as catastrophic. Accord- ing to the FAA risk matrix, such a condition is acceptable only if it occurs less than once every 100 years or less than once in 25,000,000 departures. For the second case, based on historical data of accidents and incidents, the worst credible consequence may be classi- fied as major. In this case, the risk is acceptable if it is expected to occur about once every year or every 2.5 million departures (4 × 10−7), whichever occurs sooner. The ICAO Obstacle Clearance Panel (OCP) has set the acceptable risk of collision during the approach phase at a value of one in 10 million operations (1 × 10−7). Since this is the risk level used to establish most of the airfield design stan- dards defined by the FAA, and this methodology will serve as a screening tool, this criterion is used in this screening method- ology. However, the risk classification based on the risk matrix defined by the FAA must be highlighted when submitting MOS for FAA approval (FAA, 2010). A-3 Figure A-1. FAA risk matrix (FAA, 2010).

A-4 Table A-3. FAA likelihood levels (FAA, 2010). ATC Operational Genera l Airport Specific Per Facility NAS-wide Fr eq ue nt A Probability of occurrence per operation is equal to or greater than 1×1 0 -3 Expected to occur mo re than once per week or every 2,500 departures (4×10 -4 ), whichever occurs sooner Expected to occur mo re than once per week Expected to occur every 1–2 days Pr ob ab le B Probability of occurrence per operation is less than 1×10 -3 , but equal to or greater than 1×10 -5 Expected to occur about once every m onth or 250,000 departures (4×10 - whichever occurs 6 ), sooner departures (4×10 - whichever occurs 8 ), sooner Expected to occur about once every m onth Expected to occur several tim es per m onth R em ot e C Probability of occurrence per operation is less than 1×10 -5 but equal to or greater than 1×10 -7 Expected to occur about once every year or 2.5 mil lion departures (4×10 - whichever occurs 7 ), sooner Expected to occur about once every 1–10 years Expected to occur about once every few m onths Ex tr em el y R em ot e D Probability of occurrence per operation is less than 1×10 -7 but equal to or greater than 1×10 -9 Expected to occur once every 10–100 years or 25 million Expected to occur about once every 10–100 years Expected to occur about once every 3 years Ex tr em el y Im pr ob ab le E Probability of occurrence per operation is less than 1×10 -9 Expected to occur less than once every 100 years Expected to occur less than once every 100 years Expected to occur less than once every 30 years Note: Occurrence is defined per movement. Table A-4. FAA severity definitions (FAA, 2010). Hazard Severity Classification Minimal 5 Minor 4 Majo r 3 Hazardous 2 Catastrophic 1 No dam age to aircraft but minimal injury or disco mfo rt of little consequence to passenger(s) or workers - Mini mal damage to aircraft; - Minor injury to passengers; - Mini ma l unplanned airport operations limitations (i.e. taxiway closure); - Minor incident involving the use of airport em ergency procedures - Major dam age to aircraft and/or minor injury to passenger(s)/ worker(s); - Major unplanned disruption to airport operations; - Serious incident; - Deduction on the airport's ability to deal with adverse conditions - Severe dam age to aircraft and/or serious injury to passenger(s)/ worker(s); - Complete unplanned airport closure ; - Major unplanned operations limitations (i.e. runway closure); - Major airport dam age to equipm ent and facilities - Complete loss of aircraft and/or facilities or fatal injury in passenger(s)/ worker(s); - Complete unplanned airport closure and destruction of critical facilities; - Airport facilities and equipm ent destroyed