The 1 February crash killed two IAF pilots testing the upgraded Mirage 2000 – Squadron Leaders Samir Abrol & Siddhartha Negi

New Delhi: It wasn’t pilot error but a possible lapse during the aircraft upgrade process that led to the 1 February Mirage 2000 crash at the Hindustan Aeronautics Limited (HAL) airport in Bangalore, the court of inquiry (CoI) has found.

Two Indian Air Force (IAF) pilots testing the upgraded Mirage 2000, Squadron Leader Samir Abrol and Squadron Leader Siddhartha Negi, were killed in the crash.

According to the CoI, the crash was caused by an “uninitiated control input” — or a software glitch — during the jet’s user acceptance trial.

The CoI has also faulted the arrester barrier at the HAL airport runway, saying it failed to intercept the aircraft’s slide after it crashed. The arrester barrier is a net with two hydraulic jacks that is installed at the end of runways to ensure an aircraft does not overshoot it.

HAL sources told ThePrint that since the CoI is yet to be finalised, it will be premature to comment. They added that HAL has nothing to do with the software of the aircraft.

The investigation, which is still in progress, is now trying to pin-point the exact reason behind the glitch that made the aircraft slam down after ascending five metres off the ground, top sources in the defence establishment told ThePrint.

Footage of Crash Proves Key

State-run HAL is carrying out an upgrade of the Mirage 2000 fighters, manufactured by the French firm Dassault.

According to the sources, a software glitch was the main cause behind the crash, suggesting a mistake in the upgrade process.

“Even the soldering done on the hardware can actually send wrong signals to the software, which acts accordingly,” one source explained.

The software of a fighter jet is basically the mission computer, the aircraft’s central system that controls all avionics and other systems. The aircraft involved in the 1 February crash had been subjected to six test flights by HAL, and was on its second test by the IAF when it crashed.

The entire sequence of the crash has been caught on video, and the footage, along with the jet’s black box, has proved key in unravelling the cause of the accident. The black box was sent to France for analysis.

The video shows the start of the trial, as the aircraft’s brakes are released and the flight is accelerated. At about 13 seconds from wheel roll, the sources said, the nose wheel is seen lifting off the ground with the plane taking off seven seconds later.

When the aircraft is about five metres from the ground, the sources added, its nose pitches sharply downwards, with the jet then hitting the runway on its main wheels and tail.

“This sudden action is not due to human error, the CoI has found till now,” one of the sources said.