Abnormal reaction to AP disengagement on final @ MMPR

I was approaching MMPR from a flight originated from Manchester UK on 788 today and while descending I set up a NAV1 turn for 40 degrees with the 04 runway alignment when doing the base turn as no ILS is available at this airport.
After stabilising the angle and slowing down on final approach, I disengaged the AP only to be met with the abrupt throttle cut out and ended up stalling into the ocean in a matter of secs.
I have send a copy of the replay so that it can be viewed to determine the cause of the abnormal reaction to the disengagement of the AP on final.

Ipad 8th generation (2020):
Current OS: 16.3.1

this has happened to me as well


Interesting is this with B788?

When you disengaged autopilot, the auto throttle disengages as well, which would be the reason why your speed is not being maintained. Were you trying to increase the throttle and it would not accelerate?

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It wouldn’t make sense as the throttle should be in current speed position when I was on final approach after stabilising the approach speed, flaps and gears down. I was approx 6nm away from the airport. The moment I disengaged the AP, it just went haywire lifting up and losing speed rapidly giving me almost zero chance to recover.

So it’s ether some bug in relation to 788 or is it because I have set up NAV 1 40 degrees for the base turn - I did not reset to GPS, before disconnecting AP. Would that be the cause?

I never come across this before, so my gut feeling is maybe it is due to the NAV1 settings?

Auto throttle continuously updates the throttle position, and when it is disabled the throttle will stay in its current position, regardless if that is not enough to meet the speed you set earlier, and also, what was your trim? And did you remember to calibrate?

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Exactly the throttle should stay in its position after disconnecting AP.
The approach speed was 160 IAS when I disconnected the AP, with full flaps and gears down.

I would have recalibrated the device before AP, I can’t say for definite I did. So maybe on this occasion I did not but that would be extremely unlikely as I am a guy known for details.

My trim was set 50%

with any 787, with the 789 specifically, but it has happened before and idk why

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What you’re describing seems to be wind shear. In the future I would recommend if this happens to immediately apply full power, turning off spoilers and go around, making sure to still have full power and don’t change the flaps until you can confirm you are out of the wind shear and in stable conditions

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its not a wind shear, the stall climb rate is way too steep and it is right when you disable the Autopilot or the APPR, it’s not normal, also you can see this by wind conditions, if the wind is 9 knots and you suddenly disable it, its of course not a wind shear

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Definitely it’s not wind shear, the weather conditions (METAR) did not outline this - it just a standard final approach when it just went haywire and in a matter of secs I am in the ocean lol.

I think it’s a bug associated with B788s.

It probably is a physics bug, as I now remember times when I’ve stalled on takeoff in a 787 before

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I was a little high on final approach simply because fpl waypoints no longer have set ALT. So for a moment I was holding ALT before I changed the FPM and ALT to zero so it can begin descending again on AP.

And shortly after that decided to disconnect AP for a manual landing.

It could well be to do with recalibration but I seriously doubt it as I was in the same position on departure (always recalibrate before the actual departure).

Thanks guys for the help

To do: Put enough fuel to 100, I suggest you use Nav 1 and it will allow you to use APPR To land perfectly On the centerline, be by 1200ft to let it activate the ground speed by the rectangular red squares to approach perfectly, then disengage the autopilot when you have landed at the runway

Flaps: Full
APPR: Nav 1 at RWYS and set to NAV 1 where your destination is to activate the APPR Button on Which runway you desire to land on
TRIM: 20%
Spoiler: Armed

As for this result it will improve your landings, you can look at infinite flight of How to Land with APPR, but I think you know it, do it next time when you do a flight

This to me is the puzzling part.

When not calibrated (correctly) the attitude of the aircraft may may change abruptly.
Power settings are not affected.

Being able to reproduce that would be interesting.

Were you using a controller of any kind?
With a throttle lever, that might have been in the idle position?

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No controller, just my iPad device.
The replay does show the throttle power itself did not cut off abruptly as I initially thought. So it could well be due to a calibration issue and nothing else.

I’ll reproduce this again and see.
One with calibration and one not.
I was too high anyway for this approach as I got closer to the touchdown zone because I was still on NAV1 settings for the runway heading as I made the base turn, but I turned a bit too early.

I cannot say for definite whether I have recalibrated the device for the final approach, it could be just that🤷🏼‍♂️

I must admit I don’t fly much on the 788 but it’s the first time in a very very long time this happened under my command.


Here’s the issue.

The 787 is an old aircraft in IF, therefore it has garbage physics, like you have to push down the yoke to not take off too early.

I recommend calibrating the plane every moment before disengaging the AP, and do not let the trim go over 5%

If you are flying the 787 regularly and you do not wanna met these problems again, try to vote for the 787 rework

That’s a bit harsh.

I just landed perfectly smooth with Trim set to 40.
The trim indicator wasn’t showing, indicating that is has been set correctly, so when I calibrated and disengaged the AP, absolutely nothing happened in terms of pitch.

That mainly has to do with a working cockpit and not with the physics.

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Your throttle did not cut out. Replay mode shows the throttle position if you pan down in virtual cockpit view.

At the time you cut the autopilot, your throttle simply froze in it’s last position, because the autothrottle shut off when the master AP was switched off.

As you turned off AP it also shows you added the last bit of flaps and that you manually throttled way up, apparently trying to recover the situation.

But, your trim was set at 50 (quite a large nose up setting) at the time you switched off AP, which forced your nose up into a stall.

I disagree. But I agree you recognized the issue had to do partly with the trim setting.

I think in the OP’s case, it was the high trim at the instant AP was shut off. The abrupt transition. If he had been hand flying with trim at 50, there wouldn’t have been the nose up event.

edit: just to double down on your point Jan (that the 787 is not trim flawed), I just test landed with trim at 60, without a problem.

This was a case of being out of trim at AP disengagement, intensified by the relatively low airspeed.

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