Wing flaps are moveable panels on the trailing edge of a plane's wings and provide extra lift during take-off.
Investigators did not say that the malfunctioning of the flaps caused the Spanair crash and they offered no hypothesis as to what may have triggered what was Spain's worst air disaster in 25 years.
The findings were drawn from the MD-82's flight data and cockpit voice recorders.
Alarm failure
The report said further study is needed of a malfunction of an air temperature gauge outside the cockpit, which forced the pilot to abandon a first take-off attempt.
Spanair has called it a minor glitch resolved by turning off the gauge because it was not an absolutely essential piece of equipment.
The Spanish investigators said that their initial finding might conceivably have had something to do with the failure of the cockpit alarm that is supposed to sound when a plane trying to take-off is not properly configured to get off the ground.
The data recorder shows no evidence of problems with the plane's two engines, the report added.
But the flight data recorder does reveal that from the time the plane's engines started on the runway until the crash itself, 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 alarm should have gone off in the cockpit, but "the cockpit voice recorder registered no sound from the take-off warning system", the report said.
Crash tail-first
Some of the 18 survivors have said the plane struggled to gain speed and altitude during take-off.
The report says the plane only got 12 metres off the ground.
Investigators say the aircraft crashed tail-first, bounced three times as it skidded through a grassy area near the runway, then disintegrated and burned after coming to a halt at the edge of a stream.
The report was carried in Spanish media, and Spanair confirmed it had been distributed to the government and the plane's manufacturers.
The investigators work for the civil aviation department of Spain's development
ministry.
A Spanair official declined to comment on any aspect of the investigators' report.