A preliminary report into the deadly crash of an Air India jetliner in June is expected to be released by Friday, three sources with knowledge of the matter said, with one adding the probe had narrowed its focus to the movement of the plane’s fuel control switches.

The London-bound Boeing 787 Dreamliner, which started losing height after reaching an altitude of 650 feet, crashed moments after takeoff from Ahmedabad, India, killing 241 of the 242 people on board and the rest on the ground.

The investigation into the Air India crash is focusing on the movement of the engine fuel control switches following an analysis of the 787’s flight and voice data recorders, along with a simulation by Boeing of the aircraft’s final moments, one of the sources said.

The investigation has not raised any immediate concerns over mechanical failure, the source said, and there has been no bulletin to airlines recommending changes to 787 operations.

Boeing declined to comment.

Aviation industry publication the Air Current first reported the focus on the fuel switches that help power the plane’s two engines.

It was not clear what specific actions involving the fuel switches are being looked at by investigators.

Sources told the Air Current that the available information on the black boxes could not rule in or out improper, inadvertent or intentional actions that preceded or followed the apparent loss of thrust before the aircraft crashed.

U.S. aviation safety expert John Cox said a pilot would not be able to accidentally move the fuel switches that feed the engines. “You can’t bump them and they move,” he said.

Cox added that if a switch was shut off, the effect would be almost immediate, cutting off engine power.

Most air crashes are caused by multiple factors. The investigation is focusing at least partly on engine thrust, Reuters reported last month.

While the report from Indian investigators could be made public on Friday, the three sources cautioned to Reuters that plans could change and there was no clarity on how much information would be available in the document, which comes about 30 days after the June 12 tragedy.

The sources spoke on condition of anonymity because they were not authorised to speak to media.

India’s Aircraft Accident Investigation Bureau, which is leading the probe under international rules, did not respond immediately to a request for comment outside normal business hours.

INFORMATION RELEASE

The probe has been dogged by questions over lack of information, after investigators took about two weeks to download flight recorder data after the crash. The Indian government held only one press conference on the incident, and no questions were taken.

However, India reversed course on an earlier decision reported by Reuters to prevent a U.N. aviation investigator from joining the probe, two senior sources said.

A specialist from the U.N.’s International Civil Aviation Organization (ICAO) was granted observer status, following an unusual request by the agency to offer its support.

ICAO declined to comment, adding in a statement that any public discussion of “cooperative arrangements,” would require authorisation by the state.

The crash is challenging the Tata Group’s ambitious campaign to restore Air India’s reputation and revamp its fleet, after taking the carrier over from the government in 2022.

India is banking on a boom in aviation to support wider development goals, with New Delhi saying it wants India to be a job-creating global aviation hub along the lines of Dubai, which currently handles much of the country’s international traffic.

A panel of Indian lawmakers will review safety in the country’s civil aviation sector and has invited several industry and government officials to answer questions on Wednesday, with topics set to include the recent plane crash.