MADRID, Spain — Wing flaps that help lift a plane on takeoff failed on the Spanair flight that crashed last month and an alarm to warn pilots of the problem never sounded, according to an initial report Tuesday on the accident that killed 154 people.
The investigators did not say whether they believe the flap problem caused the Aug. 20 crash that killed all but 18 aboard the MD-82. They offered no theory on what triggered Spain’s worst air disaster in 25 years.
Investigators also said they needed to further study a malfunction of an air temperature gauge outside the cockpit, which forced the pilot to abandon a first attempt at takeoff just before the crash. Spanair has described it as a minor glitch that was resolved by turning off the gauge because it was not essential equipment.
However, the report said the faulty gauge might be linked to the failure of the cockpit alarm horn, which is supposed to sound when a departing plane is not properly configured to get off the ground.
The findings were drawn from the flight data and cockpit voice recorders which showed no evidence of problems with the plane’s two engines.
A Spanair official declined to comment on the report.
The investigation found wing flaps — moveable panels on the trailing edge of a plane’s wings that provide extra lift during takeoff — failed to extend. But the pilots were unaware of the problem because the cockpit alarm did not go off.
The flight data recorder revealed that from the time the engines started on the runway until the crash, sensors measuring the position of the flaps gave a reading of zero degrees, which means they did not extend as they were supposed to.
A loud horn should have gone off in the cockpit, but ‘‘the cockpit voice recorder registered no sound from the takeoff warning system,’’ the report said.
Some of the 18 survivors have said the plane struggled to gain speed and altitude during takeoff. The report says the plane only got 40 feet off the ground.
Investigators say the aircraft crashed tail-first, bounced three times as it skidded through a grassy area near the runway, then largely disintegrated and burned after halting at the edge of a stream.
The report was carried in Spanish media, and Spanair confirmed it had been given to the government and the plane’s manufacturers.
The report said that in 1987 after another deadly MD-82 crash in Detroit, Mich., McDonnell Douglas recommended that airlines operating such planes check their take off warning system before each flight.
That disaster also occurred on takeoff and also killed 154 people on the plane — the same toll as in the Madrid crash. Two people on the ground were also killed.
U.S. investigators blamed pilot error, concluding the pilot of Northwest Airlines Flight 255 had forgotten to set the wing flaps and slats — panels on the wing’s leading edge — before takeoff.
A contributing factor was an absence of electrical power to the takeoff warning system which would have alerted the pilots that the flaps were not deployed, according to the National Transportation Safety Board. It said the reason for this absence was not determined.
Spanair’s policy is to check the warning system before a plane’s first flight of the day and during stopovers only if an entirely new cockpit crew takes over for the continuing leg, the report said.
If one member of the cockpit crew stays on — as was the case in the plane that crashed — Spanair does not carry out the checks, the investigators said.
The flight originated in Barcelona, stopped in Madrid and was to go on to Las Palmas in the Canary Islands, and the pilot and co-pilot were not relieved.
Associated Press Writer Ciaran Giles in Madrid contributed to this report.