PIPER PA-28-161 — Fort Pierce, FL

What happened

Two flight instructors were taking part in a flight school proficiency check. The instructor seated in the left seat was employed by the flight school and was administering the check to the newly-hired instructor in the right seat. The left seat instructor stated that he was demonstrating an EASA [European Union Aviation Safety Agency] maneuver at the time of the accident. He described that the maneuver involved a power-off aerodynamic stall and recovery without the use of engine power. The left seat instructor described that he pitched the airplane up and entered a full aerodynamic stall with the engine power at idle. After the airplane stalled, he recalled pitching to a glide airspeed of 73 knots to recover from the stall. He stated that during the recovery, with power at idle, the right wing departed the airplane, and the airplane banked abruptly to the right. The airplane then descended and impacted a small building that housed a recreational vehicle (RV). Both wings and the horizontal stabilator separated from the airplane in flight and were located about 600 to 700 ft away from the fuselage.

A performance study using ADS-B data and a forensic metallurgical examination of the fractured wing surfaces were conducted following the accident. The performance study found that the airplane made four steep turns in the final few minutes of recorded data before the inflight breakup. The final two 180° turns observed in the flight track data had a significantly smaller turn radius compared to previous maneuvers. The second to last steep turn had a radius of 280 ft and the airplane accelerated to over 100 knots airspeed while still in the turn, resulting in a calculated bank angle of over 70° left wing down. The final turn started with a radius of 200 ft that tightened as the airplane accelerated. With the airplane’s true airspeed at 99 knots, for a 200-ft turn radius, the resulting bank angle was over 75° left wing down. These calculated bank angles, and thus the calculation of any resulting load factors, derived from ADS-B data were approximate values that were dependent upon the accuracy of the recorded GPS data.

The Federal Aviation Administration (FAA) Airplane Flying Handbook stated in part that steep turn maneuvers consisted of single to multiple 360° and 720° turns, in either or both directions, using a bank angle between 45° and 60°. The chapter specifically provided guidance pertaining to the dangers of exceeding those bank angles and the structural limitations of general aviation airplanes.

The forensic metallurgical examination found that the left and right main spars fractured in ductile overstress following wing loads that exceeded the design capability of the airplane. The right wing likely fractured first, and the local deformation associated with the spar fracture was consistent with the upward loading on the wing. The left wing failure was secondary, showing local downward deformation at the fracture location. The left wing failure likely occurred due to a sudden elastic relaxation of the overloaded left wing in response to the rapid load change from the right wing failure, combined with downward air loads on the left wing associated with a subsequent roll to the right from the loss of lift on the right side of the airplane.

Further metallurgical examination of both the right and left wing main spar lower caps found that fatigue cracks initiated in areas of fretting damage. The cracks were not yet large enough to impact the strength of the spar under the accident loading conditions since none of the fractures initiated at or intersected any fatigue cracks. Therefore, although fatigue cracks were present, they did not contribute to the in-flight breakup.

The uniform deformation and upward bending on both sides of the spar box was indicative of a steep turn maneuver that grossly exceeded the structural limitations of the airplane. The airplane was operating in the normal category at the time of the accident. The airplane’s pilot operating handbook prohibited aerobatic maneuvers, which included turns beyond 60° of bank, and included a load limit of 3.8g while operating in the normal category.

The airplane was operated by a large flight school. The “EASA” maneuver the left seat flight instructor stated that he was demonstrating was not a part of the operator’s Instructor Briefing Sheet Test for the proficiency check being administered.

In summary, the analysis of the airplane’s flight path based on the recorded data and the postaccident metallurgical examination findings were indicative of the pilots performing a series of increasingly aggressive, aerobatic steep turns, which ultimately exceeded the design capability of the airplane, resulting in its inflight breakup. The surviving instructor reported that he was flying the airplane at the time of the inflight breakup, but his recollection of the last moments of flight and the maneuver being demonstrated was not consistent with the steep turns identified in the ADS-B performance study.

The flight school did not have a safety management system (SMS) or a flight data monitoring (FDM) program, nor were they required to have such programs. The operator did have an Aviation Safety Action Program (ASAP). A review of the ASAP database by the operator found no relevant reports involving the accident pilots or accident airplane. If the flight school had a flight data monitoring program (FDM) and safety management system (SMS), they could have had additional methods of identifying and monitoring flight data for exceedances of normal flight envelope parameters. Without SMS or FDM, flight schools have limited tools to assure that standard operating procedures are being followed.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.