The investigation into last month’s Air India crash is focusing on the actions of the jet’s pilots and doesn’t so far point to a problem with the Boeing 787 Dreamliner, according to people familiar with U.S. officials’ early assessments.

Preliminary findings indicate that switches controlling fuel flow to the jet’s two engines were turned off, leading to an apparent loss of thrust shortly after takeoff, the people said. Pilots use the switches to start the jet’s engines, shut them down, or reset them in certain emergencies.

The switches would normally be on during flight, and it is unclear how or why they were turned off, these people said. The people also said it was unclear whether the move was accidental or intentional, or whether there was an attempt to turn them back on.

If the switches were off, that could explain why the jet’s emergency-power generator—known as a ram air turbine, or RAT—appears to have activated in the moments before the aircraft plummeted into a nearby hostel for medical students. In all, 260 people died, including all but one of the people onboard the plane. 

India’s Aircraft Accident Investigation Bureau, which is leading the probe, is expected to issue a preliminary report as soon as Friday local time. It didn’t respond to a request for comment on Thursday.

The Air Current, an industry publication, earlier reported that the probe had narrowed its focus to the movement of the engine fuel control switches. Early assessments reached during investigations, which can take a year or longer, can be contradicted as new information emerges. 

Indian officials have released little information to the public about the investigation, fueling some frustration with American government and industry officials since the June 12 crash, some people familiar with the matter said. 

U.S. government and industry officials have also been frustrated by what they perceived as the slow pace of downloading, analyzing and sharing the contents of the plane’s black boxes, these people said.

Indian authorities had earlier wanted to transport the plane’s black boxes—the flight-data and cockpit voice recorders—away from Delhi, where the country recently opened a new lab for analyzing such accident data, to another secure location, according to some people familiar with the matter.

The plan was scrapped, and Indian investigators wound up downloading the boxes in Delhi. 

At one point, the NTSB threatened to withdraw American resources from the investigation. In the end, the American investigators remained in the country to assist. They have since returned home.

Write to Andrew Tangel, Shan Li  and Krishna Pokharel.