Air India Ahmedabad crash: AAIB report reveals a new mystery

A preliminary report from the probe into last month's deadly Air India crash has ruled out some possibilities while raising new ones - with the focus on a pair of switches that cut off the engines' fuel supply just seconds after take-off.

Did one of the pilots on the Boeing 787 flip the switches from "run" to "cut-off"? If so, why? Was there some other factor behind this deadly slip-up?

The report offered no hints on the answers, leaving a new mystery for investigators to unravel while regulators in several countries have begun checks of the fuel supply switches on their Boeing aircraft.

The Indian authorities gave no recommendations for action by operators of Boeing 787 Dreamliner jets or GE engines.

The crash, which killed all but one of the 242 on board and another 19 people on the ground, was the worst aviation disaster in a decade. The preliminary report had been keenly awaited for possible questions or information relating to the Dreamliner's safety record.

The probe is far from over, Air India Chief Executive Campbell Wilson said in an internal memo seen by Reuters.

Questions over pilot and air switches

Attention has now shifted to the pilots' actions in the seconds after take-off, and to the fuel switches themselves.

The report made it clear that a momentary change in the position of the switches deprived the plane of fuel at a crucial stage, leading to the crash.

Who were the pilots of the flight?

"In the cockpit voice recording, one of the pilots is heard asking the other why did he cut off. The other pilot responded that he did not do so," the report said.

A timeline of events in the cockpit

The switches flipped one second apart, the report added, roughly the time it would take to shift one and then the other, according to U.S. aviation expert and former pilot John Nance.

He added that a pilot would normally never turn the switches off in flight, especially when the plane is starting to climb.

The Airline Pilots' Association of India, in a statement, objected to the report's focus on the pilots.

"The tone and direction of the investigation suggest a bias toward pilot error. We categorically reject this presumption and insist on a fair, fact-based inquiry," the pilots' lobby said.

It also drew attention to a 2018 bulletin by the U.S. Federal Aviation Administration related to fuel switches in the Boeing 737, which are similar to those in the 787. Reports from operators had indicated that "the fuel control switches were installed with the locking feature disengaged".

The pilots' lobby called for clarity on whether the recommendations of the service bulletin were ever implemented.

The probe's preliminary report said the advisory on the fuel switches was not seen as indicating an unsafe condition that warranted specific instructions.

FAA and Boeing rejected suggestions that there were issues with the fuel switches.

On Sunday, the US Federal Aviation Administration and Boeing issued notifications that the fuel switch locks on Boeing planes were safe, Reuters news agency reported, citing documents and sources with knowledge of the matter.

The FAA's notification to Civil Aviation Authorities said: "although the fuel control switch design, including the locking feature, is similar on various Boeing airplane models, the FAA does not consider this issue to be an unsafe condition that would warrant an Airworthiness Directive on any Boeing airplane models, including the Model 787." In the meantime, authorities in India and South Korea have asked their airlines to examine fuel switches in accordance with the 2018 advisory.