6 IAF personnel onboard the chopper and a civilian on the ground died in the crash.

Highlights Air Force inquiry into shoot-down of its chopper will be over in 20 days

An Israeli-made SPYDER surface-to-air missile was launched

Final order to fire likely given after failing to identify the chopper

The Indian Air Force's inquiry into the accidental shoot down of its own Mi-17 chopper on February 27 will be over within 20 days. The summary of evidence will be presented immediately afterwards and those responsible for the death of 6 IAF personnel onboard the chopper and a civilian on the ground may be charged with culpable homicide not amounting to murder as specified by military law under the Air Force Act 1950.

Sources in the Indian Air Force have told NDTV that there was never any doubt on the outcome of the launch of an Israeli-made SPYDER surface-to-air missile on February 27 from the Srinagar air base. The investigation has taken time because the IAF is determined to apportion blame for this incident.

IAF sources have indicated to NDTV that the entire shoot-down sequence from the moment the missile was launched to the moment of impact lasted approximately 12 seconds. The Mi-17 helicopter had no means of knowing it was under attack.

NDTV has also learned of the likely sequence of events which resulted in an incorrect decision to launch the surface-to-air missile.

Between 10 and 10:30 am on the morning of February 27, eight Indian Air Force fighters were vectored to intercept upto 24 Pakistan Air Force fighters including a group of F-16s which crossed the Line of Control and fired weapons in the direction of Indian Army positions along the Line of Control in Jammu and Kashmir.

With an active air battle raging on the West, air defences across Kashmir were on the highest state of alert with surface-to-air missile units on alert and ready to engage any Pakistani aircraft which made an incursion.

It was at this same time that air defence radars at Srinagar airport picked up a low flying aircraft on their screens. The senior officer manning the post of Terminal Weapons Director (TWD) at the time was likely the Chief Operations Officer of the Air Base.

This officer may have given the final order to fire after the helicopter, designated a slow flying target, could not be identified through a critical system called the Identification, Friend or Foe (IFF) transponder.

IFF systems onboard an aircraft listen for an ''interrogation signal'' from the ground and then respond with a unique signal which identifies it as a ''friendly.'' The system is specifically designed to ensure that friendly-fire incidents are avoided during the heat of battle. It is unclear if the IAF helicopter's IFF was switched off or was not functioning at the time when it was shot down.

Sources have indicated to NDTV that a series of additional steps may not have been followed in the moments prior to the launch of the Spyder surface-to-air missile. The role of the Indian Air Force's Air Traffic Control at Srinagar airbase is also being looked at very closely by the Court of Inquiry. ATC maintains a flight plan of all aircraft that have taken off or are expected at the air base.

It is unclear whether the Terminal Weapons Director inquired and was told by the ATC that no friendly aircraft were flying in the area. It is equally unclear why details of the movement of the Mi-17 helicopter were not available with the officer in the first place.

Moments later, the order to launch was passed on to the SPYDER surface-to-air missile unit. Described as a short and medium range mobile air defence system, the system is among the newest and most advanced in the Indian Air Force's arsenal. The single missile which was launched would have quickly accelerated to Mach 4, four times the speed of sound as it sped to its target. Destruction of the slow flying helicopter, was almost guaranteed.

Senior IAF officers have denied reports that the Court of Inquiry is considering video of the shoot down of the Mi-17. According to sources, video showing the missile streaking towards the helicopter exists and is a part of the body of evidence which has been presented. 'The helicopter was 6-7 kilometres away. There is no way that a camera was present to zoom into the point of impact at that range'' say senior IAF officers.