What happened
On 28 May 2015, a student pilot was conducting a solo training flight in a Bell 206B III helicopter, registration 9M-LLM, at Kota Kinabalu International Airport. After performing a routine hover-taxi from the Layang Layang Helicopter Academy hangar to a nearby helipad, the pilot prepared for a takeoff toward runway 02.
While attempting a clockwise spot turn in a hover, the pilot observed the rotor RPM (Nr) and free power turbine RPM (Nf) indicators beginning to diverge and decrease. Distracted by the need to verify and adjust the throttle position, the pilot failed to notice that the aircraft was drifting to the right and losing altitude. The helicopter's right skid struck the ground, causing an excessive right bank that led the main rotor blades to strike the surface. The impact caused the main gearbox to detach from the fuselage and the rotor blades to disintegrate. A post-impact fire broke out near the baggage compartment, causing extensive damage to the airframe. The pilot escaped the wreckage by breaking through the windshield and sustained minor injuries.
The investigation
AAIB Malaysia examined the wreckage and the engine components. An inspection of the Allison 250-C20B engine revealed damage to the compressor wheels caused by foreign object debris (FOD). The investigation also included a bench test of the dual tachometer, which was found to be functioning normally, ruling out instrument failure as a cause. The investigation focused on the pilot's actions during the period when the engine parameters were fluctuating.
Findings
- The aircraft was airworthy and properly maintained for the scheduled training sortie.
- The student pilot was properly licensed for the flight.
- The pilot became distracted by the splitting Nr/Nf indicators and focused on the throttle position rather than maintaining a steady hover.
- The pilot, being new to the aircraft type, was unable to stabilize the throttle effectively during the emergency.
- The engine was still producing power at the time of impact, as evidenced by damage to the engine-to-freewheel coupling and the presence of FOD damage.