A preliminary report into the August crash of an airliner in Brazil found signs of ice buildup on the plane but no definite cause for the accident, the country’s Center for Research and Prevention of Aeronautical Accidents (Cenipa) said on Friday.

The document pointed out that icing detectors had been activated on airline Voepass’ aircraft, and a Cenipa official told a press conference that cockpit recordings showed the copilot said there was “a lot of icing” during the flight.

According to investigators, that comment indicates that the plane’s de-icing system might have failed, but Cenipa said that information still needed to be confirmed.

Three experts interviewed by Reuters suggested that icing could have played a role in the crash, but urged caution as the report is preliminary and accidents are caused by multiple factors.

The ATR-72 aircraft from local carrier Voepass swirled out of control before plunging to the ground on Aug. 9, killing all 62 on board.

According to Cenipa, investigations into the crash will probably last for over a year.

U.S. aviation safety expert Anthony Brickhouse said: “Everything I have read from the report today is consistent with icing, but accidents are rarely caused by one single event.”

According to officials, loss of speed alerts were triggered, but the ATR’s crew never declared an emergency situation before the plane spiraled down to the ground.

Cenipa officials on Friday also said it is still unclear to them why an aircraft with all necessary certifications ended up losing control and falling. “What we know is that the airplane was flying in an area with severe icing conditions,” said lieutenant colonel Paulo Froes.

The carrier said in a statement that the report confirmed that the aircraft and the pilots were properly certified, adding that the ATR’s required systems were in operation. It added the company would continue cooperating with the investigations.