A Tui flight taking off for the Canary Islands only cleared the A38 road next to Bristol Airport by 100ft because of a fault with the Boeing 737-800 throttles, air accident investigators have said.
The AAIB issued an alert over what it called “serious incident” as the flight departed for Las Palmas on 4 March with 163 passengers and six crew.
A fault with the jet’s auto-throttles meant it did not take off with sufficient thrust, and was only 10ft in the air as it sped past the end of the runway.
Pilots did not notice the problem, even as the plane passed over the busy A38 at 100ft – well below its intended height.
In a special bulletin issued on Thursday, the AAIB said it was looking into the fault, and how the pilots missed a routine check during takeoff.
After eventually climbing to the correct height, the flight continued to Gran Canaria as normal.
“The aircraft took off… with a thrust setting significantly below that required to achieve the correct takeoff performance,” the AAIB said.
“Despite a… requirement to check the thrust setting on takeoff, the crew did not realise that the thrust was not set correctly until after the takeoff although they had noted how close to the end of the runway they were.”
It added: “The investigation continues to examine all pertinent factors associated with this serious incident and a final report will be issued in due course”
Boeing told investigators the original autothrottle system on its 737-800s had “a long history of nuisance disconnects during takeoff mode.”
A newer version was made available in October 2021 but was not a mandatory requirement and had not been installed on the aircraft in question, the AAIB said.
A Tui UK spokesperson said: “We have worked closely with the authorities to provide all available information. The AAIB recommendations and learnings resulting from this take-off will support the whole aviation sector and other airlines. The safety of our passengers and crew is always our highest priority.”