What happened
On 18 December 2008, a King Air 200, registration ZS-NXH, was performing 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 receiving confirmation from Air Traffic Control that the gear appeared to be down during a low-level fly-past, the crew attempted to land.
During the first landing attempt, the aircraft began to sink unexpectedly, prompting an immediate go-around. Believing the issue might be isolated to the left side, 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-array. 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 initial visual inspections showed no obvious external failures, subsequent technical teardowns of the landing gear components revealed significant mechanical issues. The investigation focused on the landing gear gearbox and the electrical motor driving the system.
Testing of the gearbox revealed that the clutch assembly was not meeting manufacturer specifications. Specifically, the breakaway torque was significantly lower than the required 370 to 400 inch-pounds, and the continuous slippable torque was also below the required threshold. This deficiency caused the electrical motor to run continuously without successfully engaging the gear, eventually tripping a 60 Amp circuit breaker.
Findings
- The primary cause of the malfunction was a faulty clutch assembly within the landing gear gearbox, which prevented the motor from properly driving the gear mechanism and led to the circuit breaker tripping.
- The crew failed to utilize the manual emergency landing gear extension system immediately upon discovering the primary system failure, opting instead for two additional landing attempts.
- The emergency extension system was rendered ineffective because the left main gear actuator had been bent, likely during the crew's second landing attempt where they tried to land on the left gear first.
- The investigation also noted that the gearbox had been overfilled with grease, contrary to overhaul manual instructions, though this was not identified as the direct cause of the failure.