Indian Airlines Flight 106 departed from Bangalore for Bombay at 15:55 on a scheduled domestic flight. After a normal takeoff and climb, the aircraft was cruising at flight level 85 with the engines operating at 29″ manifold pressure and 2050 rpm. BMEP gauges were not fitted. At 16:30 hours the flight reported its position 100 miles out from Bangalore and estimated Bombay FIR boundary at 17:00. The flight was uneventful up to about 16:50 when the pilot heard a loud “thud” which he believed to be an engine misfiring. This was followed by the aircraft losing height rapidly. The auto pilot was disengaged and the aircraft was trimmed for manual flight. In order to maintain height the pilot applied climb power, and then METO power by moving the pitch and throttle controls forward, and although the manifold pressure increased first to 35″ and then to 40″, the engine speed remained constant at 2050 rpm and the aircraft continued to lose height at a descent rate of 1500 feet per minute. Cylinder head temperatures were not apparently noted. The pilot eventually made a wheels-up landing in a ploughed field at an elevation of 1900 ft. PROBABLE CAUSE: “The accident was attributed to the failure of the crew to diagnose complete loss of power caused by an inadvertent movement of the master ignition switch to the “off” position during flight.”