- Location: Vergennes, Vermont
- Accident Number: ERA24FA371
- Date & Time: September 8, 2024, 12:25 Local
- Registration: N3757T
- Aircraft: Piper PA28R
- Aircraft Damage: Substantial
- Defining Event: Aerodynamic stall/spin
- Injuries: 4 Fatal
- Flight Conducted Under: Part 91: General aviation - Instructional
On September 8, 2024, at 1225 eastern daylight time, a Piper PA-28R-180 airplane, N3757T, was substantially damaged when it was involved in an accident near Vergennes, Vermont. The non-certificated student pilot, flight instructor, and two passengers were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.
The flight instructor and owner of the airplane had been providing flight instruction to the noncertificated student pilot, who was not yet old enough to obtain a student pilot certificate. Earlier on the day of the accident, the airplane was flown from its home airport to an airport with a grass runway that was about 155 nautical miles away. About 2 hours after the airplane arrived at that airport, a witness observed the airplane as it was departing and recorded a video of its initial takeoff roll from the grass runway. Neither the witness nor the video observed the airplane’s liftoff or the accident. The airplane was later found at the accident site, which was located in a wooded area adjacent to the runway.
The airplane was equipped with brake controls only in the left front seat position, where the non-certificated student pilot was seated, so it is likely that the non-certificated student pilot controlled the airplane during at least some portion of the taxi, as it would have been difficult to maneuver the airplane on the ground without differential braking. Because the flight instructor’s logbook indicated that he had been providing instruction to the non-certificated student pilot, it is possible that she also manipulated the flight controls during the accident takeoff. Regardless, the flight instructor was the only certificated pilot aboard the airplane with access to the flight controls, and was responsible for ensuring the airplane remained under positive control. He was also responsible for intervening as necessary to maintain the safe operation of the airplane. Since the airplane was not equipped with brake controls for the front right seat occupant, if an emergency arose during takeoff that required the takeoff to be aborted, the flight instructor would not have the ability to stop the airplane using conventional braking. The only braking option for the flight instructor would be the use of the parking brake. However, there was no evidence that the accident sequence involved an attempted rejected takeoff.
Postaccident examination of the accident site and wreckage revealed that the airplane impacted terrain in a left-wing-low, nose-low attitude, consistent with an aerodynamic stall at low altitude. The main landing gear remained extended, and the landing gear control switch was in the extended position, consistent with the accident occurring shortly after takeoff. Examination of the engine revealed that the fuel injector servo throttle stop was missing the plastic material that surrounded the stop pin, which allowed the throttle to move slightly past the normal full throttle stop. The fuel injector servo was tested on a production test bench at an overhaul facility and the servo operated normally. The slight movement of the throttle past the normal full throttle stop likely did not result in a loss of power. Overall, no evidence of any mechanical malfunctions or failures of the engine were found that would have precluded normal operation.
A sound spectrum analysis of the witness video indicated that, at the beginning of the takeoff roll, the propeller was rotating at approximately 2,500 rpm. The airplane was equipped with a constant-speed propeller with a maximum governed speed of 2,700 rpm. The observed propeller speed, approximately 200 rpm below the maximum governed speed, could have been consistent with several possibilities, including the propeller governor setting, reduced engine power, or an improperly positioned propeller control. However, since the video ended early in the takeoff roll, it could not be determined whether the engine’s rpm increased further along the takeoff roll. The airplane’s tachometer was impact damaged; therefore, its accuracy could not be verified. The airplane was equipped with a digital engine monitor that recorded limited engine parameters such as the exhaust gas temperatures (EGT) and cylinder head temperatures (CHT). The last recording revealed that, at the time when recording stopped, the EGTs were at levels consistent with high engine power; though, the engine rpm and manifold pressure could not be precisely calculated. The EGTs were compared to the previous flight that day, and were comparable to those recorded during that flight. Although the available evidence did not allow the engine rpm to be determined throughout the takeoff roll, the engine monitor data provided no evidence of a loss of engine power or other mechanical malfunction that would have precluded normal engine operation.
Postaccident examination of the airframe revealed that the alternate air door was in the open position. The alternate air door was intended for use when the air filter or inlet was suspected of being clogged with debris or ice. The airplane’s alternate air door was installed in a location that would bring in unfiltered, warm air from inside the engine cowling, which typically resulted in a slight reduction in engine performance because of the lower density of the warmer air. Because the air filter was not found obstructed during the postaccident examination of the airplane, and icing conditions were not present, it is possible that the flight instructor inadvertently left the alternate air on following an operational check. According to the airplane’s Owner’s Handbook, the alternate air door should be closed for takeoff. Further examination of the airplane’s configuration revealed that the flaps were in the retracted position, which was confirmed by the witness video. The airplane’s Owner’s Handbook recommended a flap setting of 25° for takeoffs from soft fields (like the grass runway the airplane was departing from) to improve takeoff performance. Additionally, the elevator trim was found set for a slightly nose-down attitude, despite the handbook’s recommendation to trim for takeoff so that only very light back pressure on the wheel was required to lift the airplane.
Two weight-and-balance calculations were performed. One assumed the airplane departed the home airport with full fuel, and the other assumed it departed fueled to an intermediate position. The calculation for full fuel at the home airport revealed that the airplane was within the maximum weight limitations; however, the center of gravity (CG) was forward of the forward-most CG limit. The calculation for the airplane being filled to the intermediate position revealed that it was still within the maximum weight limitations and was just within the forward CG limit. A forward CG can increase the back-elevator pressure and elevator control forces required to control an airplane’s pitch, and can result in a higher stall speed.
The airplane’s configuration, including the alternate air in the open position, the flaps retracted rather than being in the 25° setting recommended for takeoffs from a soft surface, and a slight nose-down trim setting, was not consistent with the Owner’s Handbook recommendations for optimizing takeoff performance. Collectively, these configuration discrepancies likely reduced the airplane’s takeoff performance and indicate that the flight instructor had not ensured that the airplane was properly configured before takeoff. Additionally, the airplane’s likely forwardbiased CG would have resulted in a higher stall speed, and increased the risk of an aerodynamic stall. Coupled with the reduced takeoff performance as a result of the airplane’s mis-configuration, it is likely that the flight instructor lost control of the airplane during the initial climb after the airplane encountered an aerodynamic stall, resulting in an uncontrolled descent at an altitude too low to recover.
- Probable Cause: The flight instructor’s failure to maintain control of the airplane, which resulted in the airplane exceeding its critical angle of attack and entering an aerodynamic stall. Contributing to the accident was the flight instructor's failure to properly configure the airplane for takeoff from a soft surface, which reduced the airplane’s takeoff performance.
Pilot Information
According to the flight instructor’s logbook, the occupant in the left front seat had been receiving flight instruction from the flight instructor since April 14, 2024. The left seat occupant did not hold a student pilot certificate and was ineligible to obtain one due to her age; however, her age did not prohibit her from receiving flight instruction. The flight instructor occupied the right front seat. According to FAA records, the flight instructor’s most recent second-class medical certificate was issued on August 12, 2022.
No comments:
Post a Comment