Fuel Loss To Both Engines For 12 Seconds On A 94-Second Flight Caused The Crash Of AI-171, Revealed Preliminary Investigation
Mumbai: A fuel supply cut-off for around 12-seconds on a 94-seconds flight likely caused the crash of Air India’s flight AI-171 in Ahmedabad that killed 260 people, revealed the accident’s preliminary investigation. While the report eliminated the suspicion on bird hit, the investigation now focuses on the quality of fuel supplied to the aircraft.
The aircraft accident investigation bureau (AAIB) completed preparation of the preliminary report of the investigation into the crash of VT-ANB, Air India’s Boeing 787-8 Dreamliner aircraft. The aircraft flying from Ahmedabad to London Gatwick had crashed soon after take-off on June 12, killing 229 passengers, 12 crew members and 19 others while causing severe injuries to 68 people.
The preliminary report revealed all the things that went wrong in the 94 seconds from the time the aircraft started rolling on the runway to the moment it crashed. The findings highlighted that the fuel supply to both the engines was cut-off for 12 and 13 seconds respectively, which led to the loss of power to both the engines. While the ram air turbine (RAT), a small wind turbine installed on aircraft as a backup power source, started to provide hydraulic power five seconds after the cut-off, the engines started to progress to recovery only after seven and nine seconds, which was already too late to save the aircraft.
The preliminary report revealed that the fuel supply switches for both the engines transitioned from ‘RUN’ to ‘CUTOFF’ position just three seconds after the aircraft’s lift-off at 1.38.39pm. This caused both the engines to decrease from their take-off values due to loss of fuel. Although RAT was deployed during the initial climb immediately after lift-off, as seen in the airport’s CCTV footage, both the engines had already passed below minimum idle speed and the aircraft started to lose altitude even before it crossed the airport perimeter wall.
While RAT began supplying hydraulic power to the engines five seconds after the fuel cut-off, both the engines’ fuel cut-off switches transitioned from ‘CUTOFF’ to ‘RUN’ five and seven seconds later respectively. Although both the engines started to progress to recovery but could not arrest core speed deceleration leading to a Mayday call from one of the pilots and six seconds later, the black box stopped recording the flight’s information.
As fuel cut-off has been derived as the primary cause of crash, AAIB is now focusing on whether the quality of fuel caused the engines to stop working. According to the report, the fuel samples from the bowsers and tanks used to refuel the aircraft were found satisfactory. However, only a limited amount of fuel samples could be retrieved from the aircraft and they will be sent for testing at a suitable facility capable of carrying out the test with the limited available quantity.
According to the preliminary investigation, AAIB has completed the wreckage site activities including drone photography and videography. While the wreckage has been moved to a secure area near the airport, both the engines were retrieved from the wreckage site and quarantined at a hangar in the airport. It has obtained statements of the witnesses and the surviving passenger while also analysing the postmortem reports to corroborate aeromedical findings with the engineering appreciation.
Murlidhar Mohol, minister of state for civil aviation, said, “This is a primary report and not the final report. Still everything is under the purview of the investigation. The communication between the pilots has also surfaced but we should not derive any conclusion from it.”
Following the release of the report, Air India issued a statement saying that it would not comment on specific details and refer all such enquiries to AAIB due to the active nature of the investigation. It added that it is cooperating AAIB and other authorities as the investigation progresses. Similarly, Boeing also said that it is supporting the investigation but deferred to AAIB to provide information about AI-171.
Box1:
Report Raises Doubt On Human Error And Sabotage
According to the cockpit voice recorder, right after the fuel switches transitioned to cut-off, one of the pilots asked the other why did he cutoff, to which the other replied that he did not. While the report does not disclose the entire conversation between both the pilots, it leaves the investigation with a doubt on human error or a sabotage angle.
Box2:
Only One Black Box Data Could Be Downloaded, That Too With US Equipment
While several media reports had speculated that the enhanced airborne flight recorders (EAFR) or the black box will be transported to US for decoding, the preliminary report revealed that the data was downloaded in India but with the help of equipments, like the golden chassis or identical black box and download cables, sourced from the national transportation safety board of the US. AAIB could download data from only one of the two EAFR fitted on the aircraft as the data from the other EAFR could not be downloaded as it was substantially damaged. The data downloaded from the forward EAFR is being analysed in detail, said the report.
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