Primary finding
Probable cause
The stabilator trim rod assembly separated from the stabilator link assembly due to a missing connecting bolt, which resulted in the pilot’s inability to maintain pitch control of the airplane.
Investigator assessment
Analysis narrative
According to the pilot examiner, following steep turn maneuvers, they heard a loud “pop” from the tail of the airplane, the nose abruptly pitched up, and the airplane entered an accelerated stall. He took control of the airplane and added power to recover from the stall, at which time they heard another loud bang and the nose of the airplane pitched abruptly down. He reduced power to idle, there was another bang, and once again, the airplane pitched up uncontrollably. This time he did not add power and the nose of the airplane pitched down, but not as severely and he was able to use the engine power to dampen the pitch oscillations. Unable to maintain full control of the airplane, he elected for an emergency, off-airport landing. The airplane contacted trees while on approach to the field. The airplane landed hard, bounced, and slid through a rough, muddy field, which resulted in substantial damage to both wings, the fuselage, and empennage. A postaccident examination revealed that the bolt that connects the stabilator trim rod assembly to the stabilator link assembly was missing and not located. Since the bolt was not recovered, the reason for the separation could not be determined. Without being able to determine the reason for the separation, the flight school proactively inspected all same model airplanes in their fleet and replaced the bolt on each of them.
Source record
Factual narrative
On May 3, 2023, about 1329 central daylight time, a Piper PA-34-200 airplane, N28HE, sustained substantial damage when it was involved in an accident near Coldspring, Texas. The pilot examiner and flight instructor sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 pilot certification flight. According to the pilot examiner, following steep turn maneuvers, they heard a “loud metallic bang” from the tail of the airplane and the control yoke abruptly went to the full nose-up position. He stated the nose of the airplane pitched up rapidly, and the stall warning went off as they entered an accelerated stall. He took control of the airplane and applied full power to recover from the stall, at which time they heard another loud bang from the tail and the nose of the airplane pitched abruptly down. He reduced power to idle, there was another bang, and once again the airplane pitched up uncontrollably. This time he did not add power and the nose of the airplane pitched down, but not as severely and he was able to use the engine power to dampen the pitch oscillations. Unable to maintain full control of the airplane, he elected for an emergency, off-airport landing. While on the final approach, as the airplane clipped the tops of trees, the pilot examiner pulled the mixture controls to cutoff. Upon touchdown, the airplane bounced then slid through a rough, muddy field, which resulted in substantial damage to both wings, the fuselage, and empennage. A postaccident examination revealed that the bolt (item 49 in figure 1) which connects the stabilator trim rod assembly (item 12) to the stabilator link assembly (item 13) was missing. (Figure 2) Figure 1. Illustrated Parts Catalog (Part Nos. 753-816) Figure 2. Photo of the stabilator trim assembly (Photo courtesy of the FAA) A review of applicable maintenance records revealed two maintenance logbook entries for the elevator trim wheel cable becoming unspooled, the first on March 14, 2023, and the second on March 23, 2023. After each repair, a functional check flight was accomplished with no discrepancies noted. In an interview with the mechanic from the March 23 repair, he stated that he did not disconnect or otherwise perform maintenance on the affected control rod or linkage. The pilot examiner stated that during the preflight inspection, no anomalies were noted with the trim linkage assembly. Following the accident, the flight school inspected all PA-34 airplanes in their fleet and replaced the affected bolt on each airplane.