Air India replaced the Throttle Control Module (TCM) of the crashed Boeing 787-8 plane twice in the last six years following a directive from Boeing in 2019, sources said on Sunday.
TCM includes fuel control switches, which have come to focus in the ongoing probe into the fatal crash as these switches were cut off immediately after takeoff of the ill-fated London-bound Dreamliner VT-ANB that crashed in Ahmedabad on June 12.
The replacement of the TCM twice -- in 2019 and 2023 -- was mentioned in the Aircraft Accident Investigation Bureau's (AAIB) preliminary probe report into the crash that was released on Saturday. It also said the TCM replacement was not linked to the fuel control switches.
The source told PTI that a revised Maintenance Planning Document (MPD) was issued by Boeing for all the operators of the Dreamliners in 2019.
As per the MPD, the operators have to change the TCM, which includes the fuel control switches, every 24,000 flight hours, the sources said.
Since 2019, when the MPD was issued, the source said Air India changed the TCM in the ill-fated aircraft twice -- in 2019 and 2023.
Queries sent to Air India remained unanswered.
Specific details about the MPD could not be immediately ascertained.
In response to questions sent to Boeing, a company spokesperson on Sunday referred to its statement issued on Saturday saying it will continue to support the investigation and Air India.
"We will defer to the AAIB to provide information about AI171, in adherence with the UN International Civil Aviation Organization protocol known as Annex 13," the spokesperson said in the emailed statement.
AAIB, in its report on Saturday, said that at this stage of investigation, "there are no recommended actions to B787-8 and/or GE GEnx-1B engine operators and manufacturers".
Air India's Dreamliner VT-ANB, which crashed on June 12, was powered by GEnx-1B engines.
According to the report, FAA issued Special Airworthiness Information Bulletin on December 17, 2018, regarding the potential disengagement of the fuel control switch locking feature.
"This SAIB was issued based on reports from operators of Model 737 airplanes that the fuel control switches were installed with the locking feature disengaged. The airworthiness concern was not considered an unsafe condition that would warrant airworthiness directive by the FAA," it said.
AAIB also said the fuel control switch design, including the locking feature, is similar on various Boeing airplane models including part number 4TL837-3D, which is fitted in B787-8 aircraft VT-ANB.
"As per the information from Air India, the suggested inspections were not carried out as the SAIB was advisory and not mandatory. The scrutiny of maintenance records revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023.
"However, the reason for the replacement was not linked to the fuel control switch. There has been no defect reported pertaining to the fuel control switch since 2023 on VT-ANB," the report said.
After being in cut-off mode, the fuel control switches of the aircraft's two engines were turned on later but the London-bound aircraft could not get enough thrust and altitude before it crashed into a building in Ahmedabad killing 260 people.
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