What happened
On 18 December 2008, a King Air 200, registration ZS-NXH, was operating a return charter flight from Mafikeng Aerodrome to Lanseria Aerodrome. During the approach to Runway 06L, the crew noticed a lack of positive indication that the landing gear was down and locked. After a fly-past allowed Air Traffic Control to visually confirm the gear position, the crew attempted to land.
During the first landing attempt, the aircraft began to sink unexpectedly, prompting an immediate go-around. Believing the left gear might be the source of the issue, the crew attempted a second landing, specifically trying to touch down on the left gear first to force it into position. This attempt also resulted in a gear-related instability and a second go-around. On the third attempt, following a mayday call and the activation of the emergency gear extension, the aircraft touched down. The pilot maintained a nose-high attitude to reduce speed, but the main landing gear eventually collapsed. The aircraft skidded approximately 500 meters, causing damage to the rear fuselage underbelly, landing gear doors, and flaps.
The investigation
SACAA investigators examined the aircraft at Lanseria Aerodrome and later at a maintenance facility. While the landing gear motor was found to be functional, testing of the gearbox revealed a significant mechanical deficiency. The gearbox was found to be over-greased, contrary to maintenance manual specifications. More critically, the clutch assembly failed to meet the required torque standards, providing significantly less breakaway and slippable torque than mandated.
Furthermore, the investigation determined that the left main gear actuator had been bent, likely during the crew's second landing attempt when they tried to land on the left gear first. This damage prevented the emergency gear extension system from functioning effectively.
Findings
- The primary cause of the malfunction was a faulty clutch assembly within the landing gear gearbox, which caused the electric motor to run continuously until the 60 Amp circuit breaker tripped.
- The crew failed to utilize the emergency landing gear extension system immediately upon discovering the primary system failure, instead attempting two additional landings.
- The emergency system's failure to properly extend the gear was due to the bending of the left main gear actuator during the second landing attempt.