Canadian investigators have found that a Boeing 737-800 overran at Kitchener Waterloo airport after its fatigued captain inadvertently allowed thrust to increase on one engine as the other was reversing thrust after touchdown.
The Flair Airlines aircraft – inbound from Vancouver in the early morning hours of 25 November 2022 – had been conducting an ILS approach to Kitchener’s runway 26.
It had been dispatched under minimum equipment rules with the thrust-reverser of its left-hand engine inoperative. The reverser was stowed and locked in position.
Unexpectedly low cloud on the approach prompted the captain, who was flying, to “mentally rehearse” the actions for a go-around should prove necessary, says the Transportation Safety Board of Canada.
At about 300ft the captain disengaged the autopilot but left the autothrottle active – contrary to Flair’s standard approach procedure which requires both to be disengaged at the same time.
When the aircraft descended through 70ft the captain intended to disconnect the autothrottle. But instead he pressed the take-off/go-around switch. Both switches are located on the thrust levers.
While the still-active autothrottle tried to advance the thrust levers to go-around power, the captain retarded the levers to ‘idle’ and held them during the flare and touchdown, without noticing the forces from the autothrottle.
The aircraft landed 1,400ft past the runway threshold at 142kt and the speedbrakes deployed.
But when the captain removed his hand from the left thrust lever – holding the right lever in order to activate the available thrust-reverser – the autothrottle began to advance the freed left-hand lever towards go-around power.
This caused the speedbrakes to retract and the autobrake system to de-active with about 5,600ft of runway remaining.
The captain “did not realise” the left thrust lever was advancing, and he experienced “difficulty maintaining directional control of the aircraft” because the left engine was powering up to maximum thrust while the right-hand engine’s thrust-reverser was deploying.
As a result of the differential, the aircraft began to deviate towards the right-hand edge of the runway, and the captain attempted manual braking.
Some 12s after touchdown the first officer scanned the instruments and saw the left thrust lever advancing. He reached under the captain’s hand and pulled the lever back to idle, but it continued to advance – unnoticed by either pilot – when the first officer released it.
With the aircraft still travelling at 115kt, full braking was applied 16s after touchdown, with 2,500ft of runway remaining. The captain stowed the right-hand thrust-reverser and then moved both thrust levers back to idle, where they stayed.
Although the aircraft slowed, and the autothrottle disengaged automatically at 80kt, the aircraft overran the runway, travelling initially onto a paved surface before continuing on grass and stopping 500ft beyond the runway end.
None of the 134 passengers and six crew members was injured, and the aircraft (C-FFLC) sustained no significant damage, although some landing-gear pins were replaced and foreign-object debris had to be cleared.
While the captain had over 24,000h of flight experience, he had gained type rating on the 737 just seven months before the incident, joining Flair in May 2022. He had logged 542h on the type before the overrun.
The first officer obtained his 737 rating only in August of the same year, and had accumulated 182h on type.
Investigators determined that the captain had “accrued a significant sleep debt” in the week before the incident, and was operating the aircraft after a near 18h wake period – and towards the end of a low point in the circadian rhythm.
Not only had the entire flight been in darkness but, during cruise, a passenger medical situation had taken up a substantial part of the crew’s time.
“The captain’s level of fatigue decreased his attention and vigilance and increased the likelihood of a slip,” says the inquiry.
It attributes the captain’s inadvertent pressing of the go-around switch, rather than the autothrottle disconnect, to a combination of fatigue and his previously being “primed” for a possible missed approach.
While Flair’s procedures require simultaneous disconnection of the autopilot and autothrottle, the carrier’s flight-data monitoring programme showed “many instances” in which its pilot continued to use autothrottle “well after” disengaging the autopilot, the inquiry says.
Other carriers might permit this prolonged use of autothrottle, it adds, and the captain of the 737 had “significant experience” working with other operators “where this was common practice”.
Flair reminded its pilots of its requirement to disengage autothrottle at the same time as the autopilot following the Kitchener incident.
