Quantitative analysis of aircraft height on final approach

Wake turbulence encounters are a significant risk to pilots, and rules and guidance exist to ensure the safety of all aircraft operating in the National Airspace System (NAS). In poor weather and in airspace serviced by surveillance and ATC, Air Traffic Control (ATC) is responsible for separating aircraft from one another, and a conservative set of standards, including consideration of lead aircraft wake category, ensures the safety of all aircraft without requiring any input from the pilots. In good weather, when separation responsibility has been delegated to flight crews, pilots can use the situational awareness provided by direct visual contact to decrease separation between aircraft, increasing capacity to the nation´s airports. One way pilots avoid wake encounters during decreased- separation situations is by adjusting their trajectory with respect to the airplane they are following on final approach. Previous efforts have obtained qualitative feedback from pilots on their wake avoidance strategies. This paper examines actual track data from multiple sources to determine how aircraft behave in real operations for approaches to single runways as well as closely spaced parallel runways. Results confirm that pilots of smaller aircraft, generally those below about 100,000 pounds (lbs) maximum takeoff weight (MTOW), ride higher than the leading aircraft in visual conditions, whereas those over the 100,000 lbs MTOW tend not to modify their approach trajectory. Sensitivity to various parameters such as lead aircraft type, weather, distance between aircraft, and airport are examined in detail. Data on aircraft behavior for Simultaneous Offset Instrument Approaches (SOIA) for San Francisco´s International Airport are also provided. Enhancement of existing procedures or the creation of new procedures that can take advantage of the differences in altitude on approach in order to increase airport capacity, which will decrease delays at some of the nation´s busiest air- orts.