Peter Basile, Senior Air Safety Investigator, Textron Aviation, presented the case study.
The opening presentation of the 2022 the NBAA Business Aviation Convention & Exhibition (NBAA-BACE) Single-Pilot Safety Standdown featured a case study of the December 2020 runway excursion of a Cessna Citation 551 in Lukfin, Texas. Though the venue title may lead one to believe the lessons in this case study are for pilots flying in cockpits designed for a solitary pilot, the education offered here applies to all aviators.
We tend to think a runway excursion begins with an unstable approach and there is certainly much truth to that. But something that happens just prior to the approach can have an even greater impact: aircraft performance planning. For example, we obviously would never attempt a landing if the charts in our Airplane Flight Manual say the runway is not long enough. But when do you update weather and other pertinent information that might have changed since your takeoff? Safety Alert for Operators (SAFO) 06012 (since replaced by SAFO 19003), and Advisory Circular 91-79A, introduced the idea that a landing performance assessment needs to be made as close to the time of landing as possible as well as the need to add a minimum safety factor of 15% to landing distances.
The case study aircraft, N48DK, began life as a Citation 550, which requires two pilots. A service bulletin added an autopilot, flight director, and boom microphone to turn the airplane into a Citation 551, single-pilot capable. When the pilot departed Austin-Bergstrom International Airport (KAUS), the destination forecast for Angelina County Lufkin Airport (KLFK) was visual flight rules with light rain, but nothing worth worrying about. By the time the pilot checked in with air traffic control for descent, there was “moderate to heavy precipitation in and around the airport.”
The pilot elected to continue, using the area navigation (RNAV) pproach to the shorter runway, Runway 16, which was 4,311 ft. long. He asked for an approach to the longer runway, Runway 7, which was 5,400 ft. long, but the instrument approach to that runway was out due to a Notice to Airmen (NOTAM). So he elected to use the shorter runway.
Where this case study becomes especially valuable to pilots of all aircraft is the conventional wisdom codified by Advisory Circular 91-79A about the various factors that add to our landing distance. We are told, for example, that we should cross the threshold at 50 ft. and that every additional 10 ft. increases our landing distance by 200 ft. We are likewise warned about landing long, excess speed, delayed use of deceleration devices, runway slopes, and the use of less than maximum braking. But how often do we really consider all these factors when showing up at an airport where the forecast for no more than a wet runway becomes a contaminated runway with standing water?
In the case of this Citation 551, Cessna defines a wet runway to be reflective and a contaminated runway to be more than 25% covered by at least one-eight inch of standing water. Photos taken right after the accident show the runway was indeed contaminated. The performance charts predicted a 2,012-ft. landing distance on a dry runway, 4,125 ft. on a contaminated runway. So, technically speaking, had all conditions been met, the pilot could have stopped on the 4,311-ft. Runway 16 or the 5,400-ft. Runway 7. But not all conditions were met. All available evidence show the pilot touched down 1,700 ft. from the approach end of the runway and the second half of the runway had a downward slope. While the pilot used maximum braking and the condition of the tires and brakes was very good, the pilot was unable to stop on the available runway.
It is easy for an accident investigator to point to the long landing as causal in this accident, but how many of us have walked away from landing this far down the runway saying it was “a little windy today and 700-ft. long is par for the course.” How can we second-guess a pilot when the aircraft flight manual (AFM) data was “technically” good enough? That is where the FAA’s minimum recommended 15% safety factor comes in. Let us give the pilot the benefit of the doubt and say he was aware of the 4,125-ft. landing distance. Had our accident pilot added 15% to that distance and realized that (1.15) 4,125 = 4,743 ft. was more than what he had on Runway 16, perhaps the need to select another runway or airport would have been more evident.
It may be tempting to think of the 15% safety factor as just another bureaucratic attempt to further restrict us pilots from realizing the performance numbers in our manuals. But seeing how quickly a landing can go from an airplane manual to an NTSB report should underline the need to land by the book and add that factor on top. If the resulting numbers do not add up, find someplace else to land.
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