PIPER PA-31P — Myrtle Beach, SC

What happened

The accident flight was the first flight after an annual inspection during which all flight control surfaces were removed, repainted, and reinstalled. After departure, the pilot reported that he needed to return to the runway. The airplane’s altitude fluctuated between 1,000 ft and 450 ft mean sea level before radar contact was lost. Examination of the engines and propellers revealed no mechanical failures or anomalies that would have precluded normal operation. Examination of the airframe revealed that the elevator trim tabs were installed upside-down and reversed, which would have resulted in the tabs moving opposite of the intended direction. A command from the cockpit controls for nose-up trim would result in the tabs moving in the airplane nose-down direction and vice versa. As found, both trim tabs were deflected trailing edge up, which corresponded to a nose-down trim setting.

The mechanic who approved the airplane to be returned to service stated that, after the control surfaces were reinstalled, he examined the primary flight controls for proper movement but did not verify proper movement of the elevator trim tab. Although the control surfaces were tagged with labels as they were removed, those labels likely did not remain attached throughout the painting process, which contributed to their improper reinstallation.

The maintenance facility also maintained a different version of the accident airplane, which was designed with the elevator trim tab control rod and control horn positioned on the bottom of the trim tab. It is possible that the mechanic may have thought the trim tab installation on the accident airplane was the same, which could explain why the mechanic inadvertently installed the elevator trim tabs in reverse. Although the illustrated parts catalog (IPC) warned in the introduction section that the IPC should not be used for rigging and installation purposes, a figure on a subsequent page of the IPC incorrectly depicted the elevator trim tab control horn positioned on the bottom side of the elevator trim tab. Had the mechanic referred to this figure, it may have contributed to the incorrect installation of the trim tabs.

It is likely that the pilot applied nose-up trim during takeoff, and subsequently experienced nose-down trim forces due to the improper installation of the trim tab. After 2 minutes of flight, the pilot was unable to maintain control of the airplane, possibly due to the unexpected control forces, which resulted in a rapid descent and collision with terrain.

Toxicology testing detected ethanol in the pilot’s liver (0.225 and 0.078 gm/hg) and muscle tissue (0.144 gm/hg). Another postmortem microbial product, propanol, was detected in his liver tissue by one laboratory and in muscle tissue by a second laboratory. When consumed, ethanol distributes quickly and uniformly to body tissues based on water content. One would expect the concentrations in the two liver tissue samples to be similar and the concentrations in liver and muscle tissue to be similar as well. Given the different ethanol tissue concentrations, the state in which the body was recovered, and the presence of n-propanol in liver and muscle tissue, it is likely that the identified ethanol was from sources other than ingestion. Thus, the identified ethanol did not contribute to this accident.

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