Ryanair passengers who witnessed a ground collision that damaged their Boeing 737-800 and an American Airlines 767-300 failed to prevent the aircraft departing after poor crew communication led the pilots to believe the jets had not made contact.
Several passengers on the Ryanair service from Barcelona to Ibiza thought the 737 had struck the 767 as it attempted to manoeuvre behind the American aircraft, which was waiting at a holding point for runway 25L.
But although one passenger spoke to a flight attendant, Spanish investigators state that "deficiencies in the communications" between cabin crew and the pilots meant that the severity of the incident went unrecognised.
Both aircraft subsequently took off. While the 737 was later found to have a scratched starboard winglet, the 767 had a gash in its outboard left-hand horizontal stabiliser, and was withdrawn from service for repair.
A Ryanair 737 took off despite passengers reporting they had struck another aircraft
Spanish investigation authority CIAIAC, citing cabin crew statements, says that as the passenger left their seat to speak to the flight attendant, several other passengers "nervously looked out the windows on the right side".
"They were speaking in Spanish, so the cabin crew did not understand very well what they were saying," it adds. "Another passenger told them in English that some passengers thought they had hit the other [aircraft]."
But when the message was relayed to the cockpit, only a single call-chime was used - as opposed to three chimes for a serious problem - and the captain "did not sense much concern" in the flight attendant's voice.
Both 737 pilots were already aware of the tight clearance and, as the jets converged, had been in the process of verifying the separation. Shortly before the cabin call, the captain had stopped the 737 and left her seat to check the distance, and reassured the co-pilot that the two aircraft were not touching.
"The captain was under the impression that only one passenger had witnessed the contact, and not several as she later discovered," says CIAIAC.
"She said that her decision to continue with the flight would probably have been different if she had known that several passengers had reported contact."
During the flight one of the passengers - who said he was an engineer - expressed concern at the decision, under the circumstances, to proceed with the departure.
"After deplaning in Ibiza, several passengers also voiced their preoccupation over the situation," adds CIAIAC.
Neither of the pilots of the American 767 had been aware of the collision, despite the damage to the stabiliser.
CIAIAC says that while the Ryanair passengers' reports were relayed to the cockpit, the flight attendant "seems to have been unaware of the safety implication of the information she was providing", and her manner of expression indicated "hesitation" as to whether she ought to have been interrupting the pilots.
"During the flight to Ibiza several passengers expressed their unease over the incident to the cabin crew, but at no point did the [flight attendants] contact the pilots to convey the passengers' concerns," it adds.
Ryanair's procedures specifically state that cabin crew must not assume that the pilots are aware of serious problems. Investigators have nevertheless recommended that the carrier reassess its training for on-board communications.
CIAIAC says the cockpit-voice recorders were overwritten and acceleration information from the flight-data recorder could not identify the precise moment of the collision, and investigators could not draw up a detailed analysis of the geometry.
But the inquiry points out that the 767 had initially been waiting 50-60ft (15-18m) from the holding point. Its crew had been aware, from radio transmissions, that the 737 was experiencing difficulty passing behind, and subsequently moved the larger jet about 15ft closer to the holding point - although the collision had already occurred by this time.