INVESTIGATORS probing the June 12 Air India AI-171 disaster are closely examining the Boeing Dreamliner wreckage which hold “vital clues” to what could have gone wrong in the 26 seconds the flight was airborne after lift-off from Runway 23 of the Sardar Vallabhbhai Patel International Airport in Ahmedabad.Officials aware of the probe said the wreckage of the empennage or tail assembly of the aircraft showed signs of a “contained electric fire” but restricted to only a few components located in the rear. The tail had disengaged and remained largely unaffected by the post-crash explosion and fuel fire which had charred the rest of the aircraft body.The officials said components located in the tail have been identified and safely stored at a location in Ahmedabad. “They hold the key for a detailed analysis of a possible malfunction in the electric supply of the aircraft during lift off,” an official told The Indian Express.Also Read | ‘Premature, speculative’, says US probe agency NTSB chief on Air India Ahmedabad crash media reportsThe two black boxes, the clues they holdThe aft Enhanced Airborne Flight Recorders (EAFR) or the rear black box found from the rooftop of the BJ Medical College hostel mess building on June 13 had suffered extensive internal thermal damage, the officials said.The July 12 preliminary report of the Aircraft Accident Investigation Bureau, an office under the Ministry of Civil Aviation, pointed to this and said data from this “could not be downloaded through conventional means”. When it was opened to inspect the memory card, the “damage was extensive”.In contrast, the forward EAFR or the front black box, was found “burnt and covered in soot” from the charred wreckage debris on June 16, and the AAIB was able to retrieve data from this, the report said.Exclusive | Under scanner — tech snag hours before Ahmedabad Air India plane crash, if switch can cut off without pilot commandAccording to the officials, both the black boxes are housed inside robust, anti-corrosion material casing to withstand high temperatures or impact. While the rear black box relies on the aircraft’s main electrical system for power, the front black box has an independent battery to ensure it continues recording even in case of power shut down. Flight data downloaded from the front black box contained “approximately 49 hours of flight data and 6 flights, including the event flight”, the preliminary report said. The audio recovered from this, including the crash event, was two hours long.Story continues below this adThe officials said the aircraft’s tail suffered the expected crash impact when it made contact with the hostel mess building. But this was not the rare kind of damage where the aft EAFR (rear black box) should have been damaged beyond salvage, they said.“It needs to be probed if the electric fire in the tail was due to a fault that originated in one of the flight components when it began rolling for take-off, or was it purely a fire following the impact… The fire was contained in the tail section, which, despite being embedded in Building A (hostel mess), did not spread to the structure or its electrical framework,” the official said.Finding a key in the tailBesides the rear black box, the Auxiliary Power Unit (APU) located in the tail as well as the transducers and rudders of the plane are being examined, the officials said. The investigators have recovered the APU from its compartment in an “intact condition”, the preliminary report had said. It is critical to investigate the electrical fire, especially since the crew of the previous flight AI-423 from Delhi to Ahmedabad had logged a Pilot Defect Report for a status message “STAB POS XDCR” (Stabilizer Position Transducer – a sensor located in the tail) in the technical log. This was troubleshooted by the Aircraft Maintenance Engineer in Ahmedabad before clearing the flight for AI-171 at 12.15 pm on June 12.“Any malfunction of the electrical system that originated before the flight became airborne could have led to disruption of interconnected flight sensors and, in a cascading effect, triggered incorrect data to the ECU (Engine Control Unit) of the flight to cut off fuel supply… The APU also made an auto logic start after fuel supply transitioned back to ‘Run’ from ‘Cut-off’, which indicates it had been on during the take-off to have more thrust during take-off on a hot day in Ahmedabad…,” the official said.Story continues below this ad Families of victims of the Air India plane crash at the DNA testing centre in Ahmedabad. (Express Photo: Bhupendra Rana)ahmedabad plane crash, Air India 171 crash, Air India flight crash, Air India crash, air india, plane crash, plane crash ahmedabad, air india crash, air india plane crash, ahmedabad, air india flight crash, plane crash in ahmedabad, plane crash news, ahmedabad flight crash, ahmedabad news, ahmedabad plane crash, air india news, plane crash, air india flight, flight crash, ai171, air india crash, latest news, ahmedabad flight, ahmedabad to london flight, air india ahmedabad, air india share price, air india plane, ahemdabad plane crash, airindia, gujarat plane crash, meghaninagar, airplane crash, flight crash newsIt is “pertinent” that the rear black box, along with the Stabilizer Position Transducer, is located in the tail, along with the APU. “When the aircraft is on the ground, APU batteries start the APU generators. The APU generator powers the two generators on each of the two engines to start the engines. Once in flight, APU’s two generators are secondary power for the flight or used for in-cabin power,” the official said.Recalling that APU malfunctions had led to a brief grounding of the 787 series Dreamliner fleet in 2013, the officials said, the fleet was pressed back into service when the FAA (Federal Aviation Administration) approved the new design of APU battery. “The component is among the significant parts being examined now. This aircraft was pressed into service the same year after the FAA approved the new design,” the official said.The testimony of the lone survivor Viswashkumar Ramesh about “flickering cabin lights” also supports the possibility of electric malfunction, with systems switching between the main power, back-up generator, and attempted relight of systems within a few seconds, the officials said.On July 17, The Indian Express had reported that the investigators were examining the history of technical snags and the possibility of system malfunction that can impact the FADEC’s (Full Authority Digital Engine Control) Engine Control Unit (the brain of the aircraft) to trigger “uncommanded” actions. “Both engines of the flight were starved of fuel within seconds of being airborne and quickly began to decelerate… The electrical signal of transition to fuel cut-off mode, recorded in the flight data, is at the centre of the probe, which is why FADEC actions are crucial. By design, FADEC reacts to cascading malfunction in data input by triggering fuel cut off to protect engines in compromised system conditions,” the official said.Story continues below this adWhat caused the death of flight attendant in the rearThe state of the body of the flight attendant found 72 hours from the BJ Medical College building after the crash in the crew deck area of the rear fuselage also points to the cause of her death. “It was not caused by the explosion and fire like the other passengers whose bodies were charred beyond recognition. She did have some burns, which were from the fire from the aircraft’s electrical system that was brought under control when the fire-tenders arrived. But she was identified through her clothes…,” he said.An official of the Gujarat government, who was involved in the post-crash response, told this newspaper that the body was found in a highly decomposed state with post-mortem burn injuries. “The flight attendant in the rear of the plane likely died due to impact injuries. She would have been seated in the brace position and was partially affected by the fire in that section. Her body was highly decomposed due to lapse of time and the extinguishing agents used to put out the fire after the crash. Fragments of her uniform saree, made of a synthetic blend, were visible for identification.”