The wing flaps on a plane that crashed in Madrid last month did not open properly during take-off, Spanish media have reported.
Investigators found that the pilots were unaware of the problem because a cockpit warning alarm did not go off, several Spanish newspapers said, reported BBC.
The Spanair plane plunged to the ground shortly after take-off, killing 154 people on board.
It was the deadliest air crash in Spain in 25 years.
Reports in the Spanish media suggest that the Spanair jet may have stalled during take-off because the wing flaps were not properly deployed.
The flaps make it easier for aircraft to get off the ground at take-off speeds.
Investigators have not released any official statement on the disaster, but Spanish media say the issue of the wing flaps came from analysis of the cockpit voice and data recordings.
The Spanish Interior Minister, Alfredo Perez Rubalcaba, told Spanish television the government would not comment until the investigation into the crash had been completed.
"In my experience an accident doesn't happen for a single reason," he said.
"We are going to wait for the report to be finished to find out what happened because there are many theories," Mr Rubalcaba added.
The Spanair jet had aborted a previous take-off attempt.
It was preparing to fly to Las Palmas in the Canary Islands, when the pilots reported a problem.
Technicians discovered a fault in a temperature gauge on the aircraft.