What happened
On May 25, 2017, a Sikorsky S-76C++ helicopter, registration VT-CMM, was performing a non-scheduled flight from a temporary landing ground in Nilanga, Latur, to Mumbai. The flight was intended to transport the Chief Minister of Maharashtra.
During the takeoff phase, the pilot attempted to transition from a hover into a forward climb to clear nearby obstacles, including high-tension power lines. As the aircraft moved out of ground effect, the rotor RPM began to decay significantly. In an attempt to avoid entanglement with the cables, the pilot retracted the landing gear and pitched the nose up. This maneuver caused the belly of the helicopter to strike the high-tension wires, resulting in a loss of yaw control and a sharp turn to the right. The aircraft subsequently struck a tree and the roof of a truck, causing the main rotor blades to shear off. The tail rotor also struck a hut before the helicopter settled on the ground. Despite the substantial damage to the airframe and rotor systems, all six occupants—two crew members and four passengers—escaped the wreckage without injury.
The investigation
AAIB India's inquiry focused on the aircraft's performance limits and the environmental conditions at the temporary landing site. Investigators examined the Digital Engine Control Unit (DECU) and flight data recorder (DFDR) to analyze engine parameters and rotor speed. The investigation also involved a detailed weight and balance audit, comparing the crew's calculated all-up weight (AUW) against the actual weight of the aircraft, passengers, and cargo.
Findings
- The crew's calculated AUW of 10,891 lbs was inaccurate; the actual weight, including unaccounted cargo and passenger luggage, was approximately 11,183 lbs.
- The temporary landing ground was a congested area that lacked the necessary takeoff clearance distance required for Category A operations.
- The pilot attempted to initiate a takeoff in an out-of-ground-effect (OGE) configuration without sufficient reserve power to maintain altitude.
- The application of increased collective pitch to clear obstacles led to a critical drop in rotor RPM, causing the aircraft to sink.
- The decision to retract the landing gear during the descent further destabilized the aircraft and contributed to the collision with the power lines.