What happened
On 04 April 2015, an AS365 N3 helicopter, registration 9M-IGB, was conducting a private flight in Malaysia. After picking up passengers in Pekan, the flight proceeded toward Muadzam Shah. Due to deteriorating weather, the crew decided to divert toward Subang. During this diversion, the pilot executed an unplanned landing at a football field to offload a passenger.
Upon touchdown at the field, the left landing gear sank approximately 20 inches into the soft, rain-soaked soil. This caused the aircraft to tilt heavily to the left. Although the pilot repositioned the helicopter and continued the flight toward Subang with six passengers remaining on board, the aircraft' and the crew were unaware of the extent of the damage. While cruising at approximately 148 knots, the aircraft suddenly entered a steep, uncontrolled dive. The helicopter struck a rubber plantation in a ravine, resulting in 6 fatalities.
The investigation
AAIB Malaysia investigators examined the wreckage and flight data recorder (SSCVFDR) to reconstruct the sequence of events. The investigation focused on the impact of the unplanned landing at the football field and the subsequent flight dynamics. Investigators analyzed the wreckage distribution, which showed that components such as the main rotor blades, tail boom, and fenestron were scattered across a wide area, indicating significant structural disintegration in flight.
Findings
- The primary cause of the accident was the separation of the left horizontal stabiliser during flight, which induced a sudden pitch and roll that exceeded the aircraft's aerodynamic limits.
- The landing gear sinking into soft ground caused the vertical fin to strike the soil, fracturing the inboard root of the left horizontal stabiliser.
- The pilot failed to perform a thorough damage assessment following the landing gear incident, despite observing hydraulic fluid leaks.
- High-speed flight with the landing gear in the down position placed excessive aerodynamic loads on the already weakened stabilizer.
- Passenger pressure to change the flight route and return home may have contributed to the decision-making process.
Safety action
- Pilots should conduct comprehensive risk assessments regarding route suitability before departure.
- Unplanned landings at non-aerodrome sites should be avoided unless an emergency necessitates such a maneuver.
- Procedures for single-pilot operations should be reviewed, specifically regarding the safety of passenger embarkation while engines and rotors are running.
- The role of passengers in the cockpit, particularly those occupying the co-pilot seat, should be restricted to prevent interference with flight operations.