MUMBAI: Two short videos surfaced after AI-171 crashed outside Ahmedabad airport -many questions followed, from those who have flown commercial airliners. On social media, pilots were asking: 1. Why was the aircraft landing gear not retracted?2. Did the aircraft suffer a dual engine failure?3. Did the engines die because of possible fuel contamination or blockage?4. Were the flaps on the wings lowered for take-off?5. Could a bird hit have contributed to the crash?The final investigation report into the AI-171 accident, set to be released before June 12 next year, will have a detailed analysis of probable causes and contributory factors.

But for aviation professionals, the two videos offered many clues."Within 5 secs of lift off, pilots normally put the landing gear up," said Capt Amit Singh, an air safety expert. Capt Manoj Hathi, ex-Air India official who has held posts of director (ops) and director (air-safety) said: "As soon as a positive rate of climb is reached, the landing gear is retracted."A lowered landing gear increases drag and fuel consumption, while reducing aircraft speed.

Retracting the landing gear allows for a smooth aerodynamic flow helping the aircraft climb up. But the clips showed the landing gear extended even as the plane climbed to over 400 feet above ground.

What could be the reason why AI-171 had not retracted its landing gear although it had climbed to a height of around 400 feet? “In case there is a distraction the pilots could forget to put the gear up. The distraction could be dual engine failure, bird hit or combination of both.

The plume of dust as the aircraft crosses the runway end shows it was low on power and possibly a dual engine problem,” said air safety expert Capt Amit Singh.

Capt Hathi Singh, a former AI official, said, “It’s possible that a dual engine flame-out was the reason the landing gear could not be retracted. Dual engine failure could occur due to bird ingestion or fuel contamination. Looking at the trajectory and body angle of the aircraft, it appears as if the aircraft has stalled because of loss of speed.”

Other pilots spoke about dual engine failure and possible fuel contamination. The possibility of a dual engine failure is a rare event with about seven documented accidents in the past seven decades.DGCA in its statement said the pilots gave a MAYDAY call seconds after takeoff, further supporting the theory that a dual engine failure occurred probably after the aircraft crossed the speed beyond which a take-off cannot be safely aborted.

Video clips show the aircraft gliding and descending over a congested area chock-a-block with buildings. Seconds later, the aircraft nose is raised — AI-171’s pilots were probably trying to keep the aircraft from crashing in a congested locality.

But raising the nose results in loss of airspeed.The clip shows the aircraft disappear from view and crash. But even if the pilots had not pulled up the nose it would have continued to glide, descend and eventually crash, said Capt Singh.

The other point was the flaps — aerodynamic devices that are lowered to increase lift on the wing. While some pilots said the flaps were not lowered as is the norm during take-off, others said the pictures show they were lowered.Investigation into aircraft accidents carried out by civil aviation authorities such as the Aircraft Accident Investigation Bureau (AAIB) follow norms laid down in the International Civil Aviation Organisation’s Annex 13.It states that the primary objective of an investigation should be to identify and prevent incidents in the future. Under Annex 13, a preliminary report should be ready within 30 days of the event. But ICAO leaves it to the state (India, in this case) to decide whether to make it public or keep it private. The final report, though, which should be published within a year of the accident, is made public.