Primary finding
Probable cause
The pilot’s decision to attempt takeoff with frost covering the airplane’s wings, which led to an exceedance of the airplane’s critical angle of attack and an aerodynamic stall.
Investigator assessment
Analysis narrative
The pilot of the light sport airplane was preparing to depart for a cross-country flight. A witness reported that when he arrived at the airport that morning, he saw the airplane on the parking ramp, not moored down, and the engine was running. As the airplane taxied through the ramp area, he saw that it was covered with frost. Soon after the witness had gone inside the airport office, he was notified from an airplane flying over the airport that an airplane had crashed on the runway. A photo of the accident site minutes after the accident revealed that the upper surfaces of the horizontal stabilizers were covered in frost. Postaccident examination of the airframe and engine revealed no evidence of any preimpact mechanical malfunction or failure that would have precluded normal operation. Based on the witness’s statement and photo evidence, the airplane likely had frost-contaminated wings, which the pilot did not remove before takeoff. His subsequent rotation of the airplane during takeoff with its lift capability degraded due to contamination of its flying surfaces resulted in exceedance of the airplane’s critical angle of attack, an aerodynamic stall, and subsequent impact with the ground.
Source record
Factual narrative
On December 6, 2023, about 0744 mountain standard time, a light sport Remos GX airplane, N449RA, was substantially damaged when it was involved in an accident near Taylor, Arizona. The sport pilot was seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot’s family, the airplane was to depart in the morning from Taylor Municipal Airport (TYL), Taylor, Arizona, with a destination of Glendale Municipal Airport (GEU), Glendale, Arizona. The TYL airport manager reported that when he arrived at the airport that morning, he saw the airplane on the parking ramp, not moored down, and with the engine running. He noticed that the airplane was covered with frost as it began to taxi in the parking ramp area. He thought that the pilot may have been taxiing into the sun to melt the frost that covered the airplane. He further reported that it is quite common that the airplanes are moved on the ramp in the morning to melt the frost before flight. The airport manager went inside to his office and, shortly after, received a call on the radio from an airplane flying over the airport that an airplane had crashed on the runway. The airplane impacted near the centerline of the runway about midfield and came to rest inverted on the left side of the runway. A photo of the accident site minutes after the accident revealed that the upper surfaces of the horizontal stabilizers were covered in frost. Figure 1-Accident site, frost covering the upper surfaces of the left horizontal stabilizer. Postaccident examination of the wreckage established flight control continuity from each of the flight control surfaces to the cabin controls. The flaps were found in the Up position, and the elevator trim tab was found in the Up position. Onboard instrumentation was removed to download any non-volatile memory, but no accident flight data was recovered. The examination of the engine and the airframe revealed no evidence of any preimpact mechanical malfunction or failure that would have precluded normal operation. The Remos GX Pilot’s Operating Handbook (POH) describes raindrops and bugs affecting the performance of the airplane: “…raindrops and bugs affect the performance of the aircraft. Be aware that in these conditions the performance figures will not meet the published figures, as they apply to a clean aircraft under standard atmospheric conditions. Expect a significant drop in performance.” The FAA Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 12, page 12-15, pointed out that frost is a definite flight safety hazard: Frost disrupts the flow of air over the wing and can drastically reduce the production of lift. It also increases drag, which when combined with lowered lift production, can adversely affect the ability to take off. The handbook then stated on page 12-17: Aircraft that have ice, snow, or frost on their surfaces must be carefully cleaned prior to beginning a flight because of the possible airflow disruption and loss of lift.