Mumbai, Aug 3 (TOI): The Pawan Hans helicopter that crashed off Bombay High two years ago killing both the pilots on board was a result of sudden disorientation experienced by the trainee during a crucial phase of the flight and delayed action by the commander who was supervising the training flight, says the investigation report released by the Aircraft Accident Investigation Bureau on Tuesday.

In November 2015, a Pawan Hans Dauphin N3 helicopter that was on a night flying training sortie crashed into Bombay High. Days later, only the body of the trainee pilot was recovered. The investigation report says the pilot on controls (the trainee pilot) was flying during dark phase of moon at night after break of a year. "Some amount of dusk flying would have prepared the trainee pilot for undertaking the night flying manoeuvres," the report said.

The weather wasn't favourable that night with high speed tail winds and the helicopter made an approach to land on a rig that had no other rigs nearby to provide ambient lighting. "It caused an abrupt loss of visual reference. After the autopilot disconnection, the trainee pilot .... probably entered conditions ideal for black hole phenomenon because of loss of horizon wherein he was not aware about the direction he was proceeding to, that is, up or down, turning right or left,'' the report said. Black hole effect occurs during night flying when there is no moonlight or ground lights between the aircraft and the runway threshold to help the pilot gain a visual reference. It's a dangerous illusion as it leads the pilot to think that the aircraft is higher than it actually is.

After initiating a go-around, the co-pilot entered into spatial disorientation extremely quickly and the helicopter descended dangerously . The instructor cautioned the co-pilot twice, but failed to realise that the trainee was disoriented and was unable to react to his caution and the helicopter crashed into the sea at high velocity. "The commander did not take over controls when the helicopter descended below critical height. No warnings were recorded in the flight data,'' the report said.

Among the recommendations made by the report is that helidecks from where night training has to be carried out should be identified by the ONGC, in association with the helicopter operators and these helidecks should be provided with minimum landing aids for night offshore operations. The Directorate General of Civil Aviation could develop procedures for landing and take-off utilizing these aids. "As far as practicable, night flying to/from the floating vessels should not be carried out. The existing standard operating procedures on off shore departure and arrival for Bombay High should be immediately reviewed covering following aspects,'' the report said.

The report rapped Pawan Hans for not implementing in "true spirit" many recommendations made by earlier committees of inquiry though these had operational safety implications. "Even the actions taken on the recommendations have withered away with passage of time," it said.