What happened
On 2 November 2018, a Piper PA-34-220T Seneca V, registration G-OXFF, was being prepared for an instrument rating examination flight at Oxford Airport. The flight involved a student and an instructor. Following a normal start-up sequence, the emergency battery circuit breaker tripped, though it was successfully reset and voltage remained stable.
As the aircraft was taxiing toward the runway holding point, the instructor noticed that the left rudder pedal lacked the usual resistance and felt unusually soft compared to the right pedal. The instructor halted the aircraft and requested the student cross-check the controls. Upon observing the rudder movement through the cockpit door, the crew confirmed that while the right pedal functioned correctly, the left pedal produced no movement. The flight was aborted, and the aircraft was returned to the hangar.
The investigation
AAIB investigators examined the aircraft' and its Garmin 1000 avionics suite, which utilizes a standby battery for emergency power. The inspection identified that the right rudder cable had been chafing against the wiring for the standby battery. This friction caused the electrical wiring to short to earth. The intense heat produced by this electrical short was sufficient to melt through the steel-braided rudder cable, resulting in the loss of control input.
Findings
- The primary cause of the rudder malfunction was the melting of the rudder control cable due to heat from an electrical short.
- The short circuit was caused by the standby battery wiring chafing against the rudder cable.
- There were no injuries to the crew during the incident.