Indian air safety officials plan to travel to Seattle to observe Boeing’s testing of a fuel-control switch panel that was removed from an Air India 787 in February after ‌the pilots on a London-Bengaluru flight flagged a possible defect, according to documents seen by Reuters.

The testing, described by Indian officials as “sensitive”, renews the spotlight on the switches on Boeing Dreamliners that regulate the flow of jet fuel into a plane’s engines as investigators prepare a final report into an Air India 787 crash that killed 260 people in Gujarat last June.

The switches, designed to be immovable without specific actions from pilots, have come under scrutiny since the preliminary report into the crash ​found they had been shut off nearly simultaneously, starving the engines of fuel.

During the February incident in London, the pilots observed during the engine start that the fuel switches did not ​remain fixed in the “run” position on the first two attempts when light vertical pressure was applied but were stable on a third try before takeoff, ⁠India’s Directorate General of Civil Aviation (DGCA) said previously.

UK authorities investigated the incident, but Boeing privately told Air India in February the module containing the fuel switches was found to be “serviceable,” according to an email seen ​by Reuters. The DGCA had said the switches passed checks.

The module was nevertheless sent to a Boeing facility in Seattle for testing, according to confidential emails seen by Reuters being reported for the first time.

As “the ​matter is sensitive in nature, Air India is hereby directed to ensure that the strip/test examination at OEM’s (Boeing) premises is carried out in the presence of a DGCA officer,” Manish Kumar, a DGCA deputy director of airworthiness, wrote in his March 9 email.

While it is not unusual for planemakers to perform such analyses for airline customers, the email did not explain why India’s regulator considered the matter sensitive and insisted on attending.

In a statement, Air India said the module ​was confirmed as “fully functional” by Boeing and the DGCA, but the decision to proceed with further testing is “understood to be intended to ensure a thorough and conclusive evaluation ... as a measure of abundant caution.”

The ​additional testing “involves examination in a controlled laboratory environment to definitively confirm its performance and integrity,” said Air India, which is owned by the Tata Group and Singapore Airlines.

The DGCA, Kumar and Boeing did not respond to Reuters’ queries.

India ‌plans June visit ⁠to be ‘thorough’

The US Federal Aviation Administration, which regulates Boeing aircraft, has said last year’s Air India crash, the world’s deadliest in a decade, does not appear to have been caused by a mechanical issue.

Recorded dialogue between the two pilots on the flight suggested that the captain cut the flow of fuel to the engines while the first officer was flying the plane, Reuters reported last year citing a source briefed on US officials’ early assessment.

Such a prospect was denounced by a pilots’ union in India and the captain’s father, who called for an independent investigation to look into other causes.

Under international rules, a final report into the crash ​from India’s Aircraft Accident Investigation Bureau is due next ​month, and if that is not achievable, ⁠an interim update is required. The AAIB did not respond to a request for comment.

In relation to the February incident in London, the testing of the switch module is due to take place in June, the emails showed, around the time of the anniversary of last year’s crash.

The DGCA now wants to ​examine the switch’s locking mechanism, including whether external pressure applied at a particular angle could move it when locked, said an Indian government official explaining ​the reasoning behind the ⁠Seattle visit.

The Indian government “wants to be thorough”, the official said on condition of anonymity because the matter is sensitive.

Air India is paying for the trip, which will have two DGCA officials travel to the Boeing facility, said another source familiar with the matter.

While the DGCA said publicly in February the switches “were checked and found satisfactory”, the UK Civil Aviation Authority (CAA) queried the airline at the time to understand why the pilots took off with ⁠the alleged defect ​and reported the incident only on landing.

Air India at the time told the CAA the unit was found serviceable, one ​of the emails showed. In a statement to Reuters, the CAA said its review of the incident is ongoing and it “is closely monitoring Air India’s adherence to its processes.”

Boeing has said it issued a service bulletin after the February flight to all 787 ​operators reminding them of existing procedures, but it did not issue new guidance.