3 ms·

Thanks for the links. I had to go to the PDF [1] linked from the AAIB Special Bulletin to get a somewhat clear picture of the sequence of events (though if I w

Thanks for the links. I had to go to the PDF [1] linked from the AAIB Special Bulletin to get a somewhat clear picture of the sequence of events (though if I were a 737 pilot or engineer, it all might have been obvious from the summary): "Having completed their pre-flight preparation, the aircraft left the stand at Bristol to taxi to Runway 09 at 1041 hrs. The A/T arm switch on the Mode Control Panel (MCP) had been set to ARM during the before start procedures in accordance with the operator’s SOPs. The aircraft taxied onto Runway 09 at 1104 hrs and was cleared for takeoff shortly afterwards. The left seat pilot handed control of the aircraft to the right seat pilot who was to be PF for the sector. The PF advanced the thrust levers to 40% N1 and paused for the engines to stabilise before pressing the Takeoff/Go-Around switch (TOGA) which engages both the A/T in N1 mode and the autopilot/flight director system (AFDS) in takeoff mode. At this point, the A/T disengaged with an associated warning and the A/T arm switch on the MCP was reengaged by the PM almost immediately afterwards. At the same moment the PF advanced the thrust levers manually towards the required takeoff setting before releasing the thrust levers for the left seat occupant to control in accordance with the SOPs. "When the A/T arm switch was re-engaged on the MCP after initial A/T disengagement, it did not control the thrust lever servos as the pilots expected and instead entered an armed mode. As a result, the thrust levers did not advance to the required thrust setting and neither pilot moved them from the position the PF had set them to. Despite the SOP requiring that the thrust is set by 60 kt and checked as correct at 80 kt, the incorrect setting was missed by both pilots. This resulted in the aircraft takeoff being conducted with significantly less thrust than required, 84.5% N1 was used instead of 92.8% N1, with the associated reduction in aircraft performance." At this point, it is clear to me that the pilots missed two mandated checks of the power prior to rotation, but it is not entirely clear to me at what point, in this rather complicated sequence of events, things first deviated from what should have happened if both the equipment and pilots were performing as intended - was the A/T disengagement after TOGA selection the intended and expected behavior, or was the first deviation when it went into armed mode after re-engagement? [1] https://assets.publishing.service.gov.uk/media/665092d816cf36f4d63eba8f/S1-2024__Boeing_737-8K5_G-FDZS.pdf https://assets.publishing.service.gov.uk/media/665092d816cf3...

amenhotep 2y ago
Not an expert, but it seems very clear to me that autothrottle is not intended to disengage when you press the takeoff/go around button. The whole point of that button is that you press it when you need to take off or go around and the plane attempts to set itself to a configuration where as long as you point the nose in the right direction then that should happen. But it does rather sound like it was an expected behaviour. The system has a history of nuisance disconnects, the manufacturer recommends that you reject takeoff when that happens, and for some reason instead of doing that, the crew reacted to the disconnect warning by pressing the button again and, at that point, trusting that it was engaged and working. My reading of that is that the plane regularly has an A/T fault that can be fixed by simply pressing the button again, so this crew has developed a habit of doing that, but this time it was a different fault with different behaviour that their usual fix didn't work for, and they just failed to notice. The report is clearly limiting itself to describing the difference between what actually happened and what the procedures say should happen, rather than speculating about what the pilots were thinking, but that's the only way it makes sense to this very much not expert that you shouldn't pay too much attention to.
- Dalewyn 2y ago
  What's damning about the pilots is they utterly failed to monitor their engine gauges, which for those who don't know are always prominently displayed on one of the big displays near the center of the instrument panel and easily visible to anyone anywhere in the cockpit. Takeoff is by far the most stress the engines will endure during a nominal flight, it is imperative that the engines are monitored closely during takeoff in case they fail so the pilots can respond immediately. We're talking Basic Flying 101 here and these guys failed it.
  - ratg13 2y ago
    Failed to monitor their gauges and failed to do their pre-flight checklists. They might be piloting a shit vehicle, but they put no effort into doing their jobs.
- NikkiA 2y ago

amenhotep 2y ago

Not an expert, but it seems very clear to me that autothrottle is not intended to disengage when you press the takeoff/go around button. The whole point of that button is that you press it when you need to take off or go around and the plane attempts to set itself to a configuration where as long as you point the nose in the right direction then that should happen. But it does rather sound like it was an expected behaviour. The system has a history of nuisance disconnects, the manufacturer recommends that you reject takeoff when that happens, and for some reason instead of doing that, the crew reacted to the disconnect warning by pressing the button again and, at that point, trusting that it was engaged and working. My reading of that is that the plane regularly has an A/T fault that can be fixed by simply pressing the button again, so this crew has developed a habit of doing that, but this time it was a different fault with different behaviour that their usual fix didn't work for, and they just failed to notice. The report is clearly limiting itself to describing the difference between what actually happened and what the procedures say should happen, rather than speculating about what the pilots were thinking, but that's the only way it makes sense to this very much not expert that you shouldn't pay too much attention to.

Dalewyn 2y ago
What's damning about the pilots is they utterly failed to monitor their engine gauges, which for those who don't know are always prominently displayed on one of the big displays near the center of the instrument panel and easily visible to anyone anywhere in the cockpit. Takeoff is by far the most stress the engines will endure during a nominal flight, it is imperative that the engines are monitored closely during takeoff in case they fail so the pilots can respond immediately. We're talking Basic Flying 101 here and these guys failed it.
- ratg13 2y ago
  Failed to monitor their gauges and failed to do their pre-flight checklists. They might be piloting a shit vehicle, but they put no effort into doing their jobs.
NikkiA 2y ago