What happened
On 5 March 2003, a PA-30, registration ZS-NKR, was conducting a domestic charter flight from Nelspruit Aerodrome to Rand Aerodrome. While the aircraft was on its downwind leg for landing on Runway 11, the pilot attempted to deploy the undercarriage. However, the gear failed to extend fully, and the electrical motor circuit breaker tripped during the process.
In an attempt to rectify the situation, the pilot reset the circuit breaker three separate times, allowing roughly two minutes between attempts for the motor to cool. Despite these efforts, the breaker continued to trip. The pilot then attempted to use the manual extension lever to bypass the electrical torque tube system, but the undercarriage remained stuck in a partially extended position. Following a fly-past where Air Traffic Control confirmed the gear status, the pilot proceeded with the landing while the gear was not down and locked.
The investigation
The investigation examined the mechanical and electrical state of the aircraft's landing gear system. Records indicated that the aircraft's last Maintenance Program Inspection (MPI) had been completed on 25 February 2003, with only 11 flight hours accumulated since that certification. The weather at the time of the incident was reported as fine, characterized by scattered clouds and light winds.
Findings
- The investigation determined that the primary reason for the circuit breaker tripping was an overheating of the electrical motor.
- This overheating was caused by an electrical overload, which occurred because the aircraft was traveling at an excessive airspeed when the undercarriage deployment was initiated.