Why did an F-35A Crash? On July 27th, the Air Force released its report on the F-35A crash at Hill Air Force Base (AFB), Utah last October. The Accident Investigation Board (AIB) found the primary cause of the mishap to be Air Data System errors caused by wake turbulence.
Air Data System Explained
The F-35 Lightning II is the most advanced fighter jet flying today. Its many complex systems give it an incredible performance edge over other aircraft. One such apparatus is the Air Data System (ADS). This computer takes inputs from outside the aircraft such as air temperature and pressure. It uses those factors to calculate things such as airspeed, vertical speed, and Mach number values far more useful to pilots. Although air data computers have been around since the 1950s, they have been continually improved and integrated into various aircraft systems.
In the case of the F-35, the ADS is an integral part of the fly-by-wire control system where pilot inputs to flight controls like the stick and rudder are interpreted by a computer that actuates the control surfaces. By contrast, a traditional control system would have direct linkages from the stick and rudder to the control surfaces. The sophisticated flight control system in the F-35 uses ADS data to adjust control surface movement based on the phase of flight i.e. if it recognizes the aircraft is lower and slower in a position to land, it will vary how much the control surfaces move accordingly, even if the pilot provides the same inputs.
F-35A Crash: What Happened?
Last October, a flight of four F-35As was returning to Hill AFB from a routine training sortie. Upon final approach to landing, the pilot of the mishap aircraft noticed a “burble” or “rumble,” which he perceived to be wake turbulence from the preceding aircraft.
Wake turbulence is disrupted airflow generated by the passage of an aircraft, specifically its wingtips. The ADS onboard the mishap aircraft became confused by this disrupted airflow and began providing incorrect data to the other flight systems.
This caused the aircraft to depart controlled flight. The pilot attempted to recover by going to full afterburner but it was too late. Fortunately, the pilot was able to successfully eject.
Cause and Effect
After reviewing all the pertinent information and documents, the AIB faulted the ADS for causing the crash. While it is somewhat alarming that the system could become confused due to wake turbulence, particularly as many F-35 pilots have reported flying through such turbulence – a not uncommon event – the AIB did stress that this is the first time this has happened in over 600,000 flight hours for the F-35.
Furthermore, they noted that the pilot failed to follow wake turbulence procedures, which specified a greater distance between landing aircraft, although it is unclear whether he knew they were in effect at the time.
As the Air Force’s newest and most advanced fighter jet, the F-35 Lightening II platform will lead the service for years to come.
Maya Carlin, a Senior Editor for 19FortyFive, is an analyst with the Center for Security Policy and a former Anna Sobol Levy Fellow at IDC Herzliya in Israel. She has by-lines in many publications, including The National Interest, Jerusalem Post, and Times of Israel. You can follow her on Twitter: @MayaCarlin.