What happened
On a scheduled domestic service departing HAL Airport in Bangalore for Bombay, the aircraft was carrying 30 passengers and 6 crew members. The flight proceeded normally following takeoff, climbing to a cruising altitude of flight level 85 with engines set at 2050 rpm and 29" manifold pressure. At approximately 16:30, the flight reported its position roughly 100 miles from Bangalore.
The situation changed around 16:50 when the pilot experienced a loud thud, which was initially perceived as an engine misfire. Immediately following this sound, the aircraft began a rapid descent. The crew disengaged the autopilot and transitioned to manual flight controls. In an attempt to recover altitude, the pilot increased power by adjusting the pitch and throttle. While the manifold pressure rose from 29" to 35" and eventually 40", the engine speed failed to increase, remaining stuck at 2050 rpm. The aircraft continued to descend at a rate of 1500 feet per minute.
The flight ended with a wheels-up landing in a ploughed field situated at an elevation of 1900 feet. Although the aircraft sustained damage beyond repair, there were 0 fatalities and all 36 occupants were evacuated from the scene without injury.
Findings
The investigation determined that the loss of engine power was caused by the inadvertent movement of the master ignition switch to the off position during the flight, which the crew failed to identify in time to prevent the descent.