Air India replaced the Throttle Control Module (TCM) of the crashed Boeing 787-8 aircraft twice in the past six years, in line with a 2019 directive issued by Boeing, news agency PTI reported on Sunday, quoting sources.
The Throttle Control Module (TCM), which houses the fuel control switches, has become a key focus in the ongoing investigation into the fatal crash of the London-bound Dreamliner VT-ANB, after it was revealed that these switches were turned off immediately following takeoff from Ahmedabad on June 12.
When was TCM replaced?
The Aircraft Accident Investigation Bureau's (AAIB) preliminary report, released on Saturday, noted that the TCM had been replaced twice — once in 2019 and again in 2023. However, the report clarified that these replacements were not related to the fuel control switches, which are now under scrutiny in the ongoing investigation into the crash.
According to the PTI sources, a revised Maintenance Planning Document (MPD) was issued by Boeing for all the operators of 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.
What did the AAIB report reveal?
AAIB, in its report on Saturday, said that at this stage of the 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, the Federal Aviation Administration (FAA) had issued a Special Airworthiness Information Bulletin (SAIB) on December 17, 2018, highlighting concerns about 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.
(With PTI inputs)
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