Investigators probing the June 12 crash of Air India flight AI-171 from Ahmedabad to London Gatwick are taking a close look at a February 2020 incident in Gatwick, involving an Airbus A321, in which both engines malfunctioned immediately after takeoff. It led to a Mayday call before the aircraft returned to Gatwick 11 minutes later after a turnaround.

In its 2020 investigation, the UK Air Accident Investigation Branch (AIIB), which is also in Ahmedabad to probe the June 12 crash, found that the reason for the engine failure was fuel system contamination even though engineers had found no fault prior to clearing it for flying that night.

Officers aware of the ongoing investigation into the Ahmedabad crash said a thorough scrutiny of AI-171’s technical logs in the 24 hours preceding the crash were being looked into as it was “clear from visual observation and wreckage” that the flight suffered a power failure.

Story continues below this ad

Speaking to The Indian Express Thursday, an officer said the probe agencies, in primary observations from the available visual evidence, statements of the controllers of Ahmedabad Air Traffic Control (ATC), maintenance engineers who cleared the flight on the ground, and initial inspection of the wreckage, estimated that the aircraft experienced power failure of the main electric system within seconds of takeoff.

“The material evidence, which includes the wreckage and the videos of the takeoff as well as the crash, indicate a definite power failure on the flight. The cause will be known only when the black box data is recovered but we can estimate that since the flight was in a takeoff and its nose pitched up for the liftoff, the deployment of the Ram Air Turbine (RAT) could not help the flight make a safe turnaround as it had not even achieved the minimum altitude of 3600 feet for a safe path,” the officer said.

The black boxes and the DVR have been recovered but the officer said that the devices were damaged and file extraction would “be a complicated process”. According to the officer, “deliberations were on” about sending the black boxes to the US where the National Transportation Safety Board (NTSB) could help recover the recordings with advanced expertise.

The wreckage of the Dreamliner, the officer said, had “not hinted” at any cockpit error, and the pilots “may have tried their best to gain manual control” for attempting a turnaround.

Story continues below this ad

“It does not appear to be a cockpit error… The observations are that the power failure occurred as soon as the flight was airborne and was unable to climb to the safe path altitude… the (Boeing) 787 Dreamliner has a provision for a manual reversion control system to allow pilots to regain control of critical systems in the event of a hydraulic failure. This system is a backup, using RAT to generate power, but there was no altitude cushion to ensure a safe glide downward or for the pilot to attempt anything… It just dropped on to the medical hostel building, with the tail being impacted and separated due to its liftoff position. Had it achieved an elevation of about 3600-4900 feet, it could have been a different story as planes can safely make Mayday landings with the RAT,” the officer said.

AI-171 had gained an altitude of only 625 feet when it came crashing down.

The officer said that while probing the cause of engine failure, the most crucial aspect would be an analysis of the technical log of the aircraft for the preceding 24 to 48 hours to ascertain if any technical abnormalities had been experienced or noted down by the previous captains or maintenance staff.

“The aircraft was incoming from Paris to Delhi and from Delhi to Ahmedabad… In fact, it made a round trip to Paris from Delhi on June 11-12. Just a day earlier, it had returned to Delhi after a round trip to Tokyo. We will check the technical logs to see if any of the engineering teams or pilots of the previous flight left comments on the performance of both engines or experienced any ECAM (Electronic Centralised Aircraft Monitor) message during the flight, accompanied by any thrust issues during flight,” the officer said.

Story continues below this ad

“At this point, we have no reason to speculate a sabotage but if the cause of the engine failure is fuel contamination, which is most likely due to water, the maintenance records of the flight, which are also under scrutiny, will reveal if it was due to oversight or negligence or corrosion in the fuel system, leading to clogging which is rare if the aircraft is regularly serviced. Fuel contaminated with water is the most common cause of power loss in flights and, many times, cannot be detected until the aircraft is actually airborne,” the officer said.

Since the Ahmedabad crash is the first involving a Boeing 787, investigators are “leaving nothing to chance”. “The Dreamliner has an advanced electrical system… it can cover a sufficient distance safely on one engine as well… In case of dual hydraulic failure, the flight can be on manual reversion and be controlled for safe landing at the nearest available facility. The flight data recorder and the cockpit voice recorder will reveal what went wrong in about one minute,” the officer said.

A chemical analysis of “important and relevant” parts from the wreckage will reveal any unusually high level of contaminants. “Since the explosion and the subsequent fire have damaged much of the aircraft, especially the fuel tanks, forensic engineers of the investigating team have gathered as much relevant debris as possible to find traces of elements that could indicate if there had been fuel contamination,” the officer said.

The UK AAIB team is comparing notes with the February 2020 Gatwick incident findings. “The entire duration of the flight was 11 minutes, as per the investigation of the UK AAIB… The incident was almost similar, except that the flight had gained an altitude of almost 3580 feet and was able to make the roundabout and touch down after declaring Mayday thrice… The findings of the investigation had concluded that the reason for the engine failure was fuel system contamination even though the engineers had found no fault prior to clearing it for flying that night,” the officer said.

Story continues below this ad

“However, that investigation had revealed that the three flights, which the aircraft completed prior to the Gatwick takeoff, had experienced unusual signs of one of the engines as it had taken multiple attempts to start… and also relayed stalling messages during the flight… It was later found that the engineers who cleared the flight from Gatwick had not conducted extensive examination of the engine, which resulted in ‘no fault’ being found,” the officer said.