Accident Overview
On November 17, 2009, at approximately 0745 central standard time, a Piper PA-34-200T Seneca, registration N8297P, was substantially damaged during a forced landing near Saginaw, Texas. The personal flight was conducted under Part 91 without a flight plan. Visual meteorological conditions prevailed. The pilot, the sole occupant, was not injured. The flight had just departed from Hicks Field (T67) in Fort Worth, Texas, and was en route to Arlington Airport (GKY) in Arlington, Texas.
Pilot Actions
According to the pilot's account to FAA inspectors, he did not engage the autopilot after takeoff. He used the electric trim switch on the control yoke to establish a climb attitude. Upon activating the trim switch, the airplane pitched down rapidly. Despite applying full back elevator, the descent continued. The pilot executed a forced landing in an open field, during which both wings and the fuselage sustained substantial damage. Post-accident cockpit examination revealed all circuit breakers were closed and the master switch was secured.
Examination Findings
The airplane was recovered to Air Salvage of Dallas, where on December 3, 2009, FAA and Piper officials examined it. The pilot reported that the two autopilot units had been recently overhauled but had not been aligned. Piper Aircraft noted that neither the autopilot nor the trim switch wiring were factory-installed. The pitch trim drum inner shaft was found in the full nose-down position.
The airplane was equipped with a KFC-200 autopilot system and a KI-256 flight director. The original control yoke trim switch had been removed and a replacement switch installed. The switch wiring was not original and did not match the original color codes; pieces of masking tape with handwritten color labels were wrapped around the wires.
Component Testing
The flight computer, trim servo, directional gyro, flight command indicator, pictorial navigation indicator, and control yoke were sent to Honeywell in Olathe, Kansas. On January 13, 2010, they were examined and functionally tested. According to Honeywell's report, no defects were observed that would explain why the pitch trim was found in the full nose-down position. However, Honeywell found that one wire was pinched and pressing on the switch wafer stack. Tests were inconclusive as to whether this might have caused an internal short in the switch.
In an email to the investigator, a Piper representative stated that Honeywell indicated the chafing was probably not an issue, but the pinched wire pressing on the switch wafer stack might have caused an internal short.