ANC24FA085

The pilot's exceedance of the airplane’s critical angle of attack while maneuvering for landing, which resulted in an aerodynamic stall and loss of control.

The airplane departed from a remote hunting camp and traveled to a 2,500-ft ridge about 3.5 miles away to drop off supplies to a hunting guide; the pilot was planning to continue to an airport for fuel. According to the guide who was at the scene of the accident, the airplane flew over their camp several times before flying further up the ridge, where it executed several passes over the ridge. While the pilot had landed on this ridge in seasons past, this would have been his first time landing on the ridge this year. The guide reported that winds near the accident site were about 15 mph from the northeast and the visibility was good. He reported that the airplane was traveling slow and low on a southwest heading and began a right turn to the northeast. As the airplane began what the guide thought to be a right base to final turn, he lost sight of the airplane. However, the guide reported that he could still hear the airplane’s engine. He reported hearing the engine “call for a lot of power” twice and a few seconds later he heard the airplane impact the ground. The airplane was found nose down in a near-vertical attitude on a northeast heading on the south side of the ridge. The wings remained partially attached and the tail was bent slightly to the right. The wreckage pattern of the airplane was consistent with the airplane impacting the ground during a stall/spin. The pilot and owner of the accident airplane had incorporated modifications to the airplane, including leading edge slats and slotted two-piece flaps. The leading edge slats were removed a few months before the accident. Although these modifications allowed for lower airspeeds during landing and altered the stall characteristics of the airplane, the investigation was not able to determine if the changed flight characteristics might have played a role in the experienced pilot’s exceedance of the airplane’s critical angle of attack while maneuvering. A postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. Based on the available information, it is likely that the pilot exceeded the airplane’s critical angle of attack while maneuvering for landing, which resulted in an aerodynamic stall and loss of control.

On August 31, 2024, about 1000 Alaska daylight time, a Piper PA-18-150 airplane, N7154Z, sustained substantial damage when it was involved in an accident near McGrath, Alaska. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 business flight. The airplane departed from a remote hunting camp and traveled to a 2,500-ft ridge about 3.5 miles away to drop off supplies to a hunting guide; the pilot was planning to continue to McGrath for fuel. According to the guide who was at the scene of the accident, the airplane flew over their camp several times before flying further up the ridge, where it executed several passes over the ridge. While the pilot had landed on this ridge in seasons past, this would have been his first time landing on the ridge this season. The guide reported that winds near the accident site were about 15 mph from the northeast and the visibility was good. He reported that the airplane was traveling slow and low on a southwest heading and then it began a right turn to the northeast. As the airplane began what the guide thought to be a right base to final turn, he lost sight of the airplane. However, the guide reported that he could still hear the airplane’s engine. He reported hearing the engine “call for a lot of power” twice and a few seconds later he heard the airplane impact the ground. The airplane was found nose down in a near-vertical attitude on a northeast heading on the south side of the ridge. The wings remained partially attached and the tail was bent slightly to the right. Based on witness statements, as well as pictures and videos from the pilot’s website, the accident airplane previously had leading edge slats and slotted two-piece flaps installed from 2020 until sometime in 2023-2024 (see Figures 1, 2). The bolt pattern observed on the leading edges of the accident airplane’s wings resembled that of the Mackey Slats (see Figure 3). However, engine and airframe logbooks could not be located so exact details were not available. Leading edge slats and slotted two-piece flaps change the flight characteristics of a conventional airplane by reducing the maneuvering speed. There is currently no Supplemental Type Certificates (STCs) for leading edge slats; therefore, airplanes with these installed are not approved for passenger-carrying operations. The FAA was notified in October 2022 that the pilot may have been flying passengers in the accident airplane with the leading edge slats installed, and the FAA contacted the pilot regarding the installation of the leading edge slats. The pilot reported that he was helping a manufacturer obtain an STC for the leading edge slats and denied flying passengers with leading edge slats installed. The pilot/owner removed the leading edge slats sometime in the spring of 2024, after his interaction with the FAA. A postaccident examination of the airframe and engine revealed no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. Figure 1 Accident airplane with slotted two-piece flaps and leading edge slats Figure 2 Accident airplane with leading edge slats Figure 3 Leading edge slat attachment points on wing of accident airplane