Posts by user "M.Mouse" [Posts: 8 Total up-votes: 0 Pages: 1]

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M.Mouse
June 16, 2025, 23:23:00 GMT
permalink Post: 11903868
I do not wish to speculate on the cause of this horrible accident but
Except for the initial conversation about mistakenly retracting flaps instead of landing gear, which eventually was dismissed in favor of engine failure as there has been an almost unanimous agreement that even if such mistake was made, it was recoverable.
this vey situation happened to a good friend of mine, former Tornado pilot with 25 years on airliners, as a captain and PF on a B777. In his words he was initially totally confused why the aircraft stopped climbing. He engaged the autopilot and quickly realised the problem but they came very close to stalling.

I would not like to place money on how quickly I would recognise the, highly unusual, situation of flaps being retracted with the gear remaining down and react appropriately.

The Air India flight was circa 30 seconds from lift-off to crashing.

I am sure an initial report will soon publish the basic facts.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Engine Failure (All)

M.Mouse
June 18, 2025, 00:23:00 GMT
permalink Post: 11904796
In any case the autopilot wouldn’t have been in at such a low altitude and the PF would have been hand flying. Most of the min engagement altitudes for autopilots is 400’ AGL.
Minimum autopilot engagement height on the B787 is 200'.

767 pilot here, on the 767 it would capture the altitude, but more importantly, it would freeze the airspeed at whatever speed the alt capture occurred at. So the thrust levers would retard to maintain the much slower speed at the point of capture. This could be a possible scenario, especially if the crew was slow to realize what happened, AND the 787 has a similar low altitude capture issue.
On the B787 if VNAV is engaged and the aircraft captures an altitude below the programmed acceleration height then the vertical mode transitions to VNAV ALT and commences acceleration to the current flap setting limit speed -5 knots.

Subjects: None
M.Mouse
June 18, 2025, 12:59:00 GMT
permalink Post: 11905219
Assuming then that VNAV in the 78 engages at 200` AGL vice the 400` of the 777 ?
On the B787 the VNAV, if armed, engages at 400'.

Subjects: None
M.Mouse
June 18, 2025, 15:50:00 GMT
permalink Post: 11905350
VNAV hasn\x92t engaged yet in that scenario. So do I get SPD LNAV ALT ?
Usually on takeoff LNAV and VNAV are armed. During the takeoff roll the autothrottle system goes in to HOLD mode at 80kts.

At that point the FMAs read:



At 50' LNAV engages and the FMAs change to:




At 400' VNAV engages and the FMAs change to:




The height is referenced to a barometric snapshot taken during the take off roll at 100kts.

If an altitude is captured before VNAV engagement (totally bizarre to capture an altitude of less than 400') then the FMAs would change to:

SPD | LNAV | ALT

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Takeoff Roll

M.Mouse
June 18, 2025, 17:40:00 GMT
permalink Post: 11905419
A mate tried gear/flap scenario in the sim earlier. Selecting flaps up (all the way) instead of the gear did not predjudice the flight path at all. They selected flaps up at normal gear retraction height and punched the AP in. The Slats remained out until 225kts (as per my post about 50 pages ago) and the aircraft climbed happily away clearing all obstacle by a good margin.
Was that using the same aircraft weight, same flaps, same ambient temperature and with the same de-rate(s) as the accident flight? Presumably he had inside information to find the appropriate numbers?

Subjects: None
M.Mouse
June 19, 2025, 14:25:00 GMT
permalink Post: 11906063
It then automatically re-engages at 400ft AGL (though I am not sure how the altitude is measured), and begins to operate as requested by various human and computer systems.
At 100 knots during the takeoff roll the systems take a snapshot of the barometric altitude at that point. The 400' for VNAV engagement, if it is armed, is based on that datum.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Takeoff Roll

M.Mouse
June 19, 2025, 15:10:00 GMT
permalink Post: 11906101
A question to those familiar with Boeing and the 787: are the thrust levers physically moved by Autothrust or does Boeing use them only to stake an upper thrust limit as Airbus does with active A/T?
The B787 autothrottle system physically moves the thrust levers when varying the power required.

Subjects: None
M.Mouse
June 20, 2025, 22:29:00 GMT
permalink Post: 11907367
he autopilot would NOT be engaged below 400’ (or 200’ in the 78–although I doubt anyone engages it that low. The autopilot and autothrottles are separate systems but do interact. The autothrottles typically WOULD be engaged from the start of the takeoff roll; using the TOGA levers to set takeoff thrust).
Both the B777 and B787 have a minimum autopilot engage height of 200'. I would suggest it is often the best course of action after an engine failure to engage the autopilot at 200' to dramatically reduce the workload!

I am guessing because although I flew the 777 I never tried a low altitude capture before VNAV engaged — and it`s been a few years). But think it probably would. As one goes through 50’ LNAV engages; VNAV is normally armed prior to the EFIS check if it`s to be used (which it usually is). So in this scenario LNAV would have been engaged but since VNAV is armed but never engages my guess is that the automatics would engage in SPD/LVAV/ALT.
When talking about low altitude capture below the 400' VNAV engagement height, although it has been talked about, would mean (mis) setting the MCP altitude to less than 400'. I really find that implausible. You are correct though that the modes would be SPD | LNAV | ALT should this occur.

HOLD is present in many other regimes of flight; all it means is that the auththrottle (right now) is not controlling the throttles and they stay where they are—and the PF can move them if desired at will. Fr` instance, when descending in FLCH or even VNAV SPD the throttles will usually be in HOLD. (To me this usually meant `hold` the throttles—and tweek them in descent as required). Thrust can be modulated to adjust rate of descent (the throttles become vertical speed levers). On altitude capture in the case of FLCH or path capture in the case of VNAV SPD (in descent) the auththrottles kick in and it becomes SPD/xxx/ALT (or VPTH or VALT as the case might be).
All correct.

Most everyone knew the autothrottles would not engage below 400` and that FLCH in descent at very low altitudes was not an appropriate mode — and they did not activate providing low speed protection in the case of Asiana.
The lack of autothrottle automatic activation when the autothrottles are in HOLD mode and the speed has decayed below minimum manouevring speed has been addressed. The autothrottle will now automatically activate if, when in HOLD mode, the speed decays below minimum manouevring speed with FMC software after BP4 on the B787 and after AIMS V17B on the B777.

Since the Asiana accident many airlines prohibit use of FLCH below 1,000' and the lowest altitude setting when using FLCH is then, of course, 1.000'

IIRC our throttles went into HOLD at 60 knots and stayed there until VNAV activated (THR REF—takeoff thrust). It was also possible that the autothrottles under some environmentals wouldn`t fully achieve takeoff thrust setting (EPR or N1 depending on which engines) and they could be manually moved in HOLD to achieve it. Although I don`t remember that as ever happening.
Almost fully correct, the speed when autothrottles transition to HOLD on takeoff is 80kts. on both the B777 and B787.

Subjects (links are to this post in the relevant subject page so that this post can be seen in context): Engine Failure (All)  TOGA  Takeoff Roll

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