nolimitholdem
2025-06-12T09:48:00
permalink Post: 11898954

Quote:

Originally Posted by Tu.114

How does a 787 react to low speed? What are the protections on this type?

Full suite of typical FBW flight envelope warnings and protections from initial "Airspeed Low" EICAS caution to inability to trim to autothrottle activation and pitch down, stick-shaker at onset of stall etc.

But nothing can protect against laws of physics that apply when there isn't just enough energy for a (possibly) shortened takeoff distance and misconfigured aircraft.

Very sad, and bewildering.

Subjects: FBW

5 users liked this post.

nolimitholdem
2025-06-12T10:15:00
permalink Post: 11899017

To address a couple points raised as best able:

• B787 does have takeoff config warning, but for the flaps will only warn if a valid takeoff flap setting isn't selected - doesn't crosscheck against the FMC, and there is a range of valid settings (UP and 1 are not valid settings)
• Similar to Airbus there is LE Autoslat extension for low speed protection.
• That EK B777 freighter referenced may have been lightly loaded and generally speaking has far more excess thrust than a B787. Intersection takeoff could be quite valid for the former, having flown both I would be much more hesitant (read: not a chance) to take an intersection in the B787 without an incredibly compelling reason even if the OPT says it's possible.

Subjects: Flap Setting Flaps (All)

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nolimitholdem
2025-06-12T11:05:00
permalink Post: 11899071

Quote:

Originally Posted by Chesty Morgan

Can someone tell us the retraction schedule for 787 slats and flaps. I guess similar to the 737 where the slats retract after the flaps...?

Correct. The flaps and slats sequence so that the LE slats extend first and retract last.

I'm wondering if the takeoff required a Flaps 15 settings but Flaps 5 was set instead in error. Wouldn't be impossible to do, given that the vast majority of takeoffs are Flaps 5 so muscle memory and confirmation bias set in. That wouldn't trigger a config warning, but would leave the a/c in a poor energy state. If indeed an intersection takeoff (which is not confirmed) there'd be zero margin left.

Subjects: None

3 users liked this post.

nolimitholdem
2025-06-12T11:14:00
permalink Post: 11899084

Quote:

Originally Posted by Gary Parata

787 driver here. The BEFORE TAKEOFF electronic checklist will not show as completed unless the flap position indication agrees with the flap setting entered into the CDU. If that is missed, a CAUTION is issued: CHKLIST INCOMPLETE NORM as the aircraft lines up on the CDU-entered runway.

Hmm. B787 pilot also and with respect, on the B787 (-9 tho) in the sim anyway, wanting an answer to this very question we experimented with setting a flap setting other than the one in the CDU and received no config warning. I believe the config warning system reads the flap position sensors, not the CDU. I am completely willing to be corrected but was quite surprised myself. 🤔

Subjects: Flap Setting Flaps (All)

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nolimitholdem
2025-06-12T12:41:00
permalink Post: 11899168

Quote:

Originally Posted by Kenny

777 guy but you’re talking about two different things. Unless I’m mistaken. You’re talking about the Take Off Config EICAS warning. He’s talking about the Before Take Off checklist showing as complete, if the selected flaps aren’t in agreement with the entered CDU value.

Correct. Two different things, sorry if I muddied the water. Also former B777 guy. Would love to go back but that's a different conversation. 😁

Subjects: None

1 user liked this post.

nolimitholdem
2025-06-13T14:15:00
permalink Post: 11900554

Quote:

Originally Posted by xetroV

Video evidence suggests at least the leading edge devices were extended:

https://youtu.be/oUFS2np0mKc?si=0f1Td6bQiqNOE4U-

LE devices extended on impact would correspond with the B787 auto-gap function that extends the slats in certain low-speed high AOA conditions for stall protection (aka "Autoslats"). Which this aircraft most certainly was in before impact.

Only to say, that LE devices seen extended on the crash a/c don't prove configuration on takeoff.

B777/787 rated/current/active pilot.

B787 FCOM:

Quote:

The slat autogap function is only available in primary mode when the slats are in the middle position and the airspeed is below 225 KIAS. At a high angle of attack, autogap fully extends the slats to increase the wing camber, thus increasing the lift and margin to stall. The slats return to the middle position after the angle of attack decreases. The autogap trip threshold is a function of AOA, airspeed and flap position.

Last edited by T28B; 13th Jun 2025 at 16:58 . Reason: Formatting assistance

Subjects: FCOM Flap Setting Flaps (All)

9 users liked this post.

nolimitholdem 2025-06-12T09:48:00 permalink Post: 11898954	Quote: Originally Posted by Tu.114 How does a 787 react to low speed? What are the protections on this type? Full suite of typical FBW flight envelope warnings and protections from initial "Airspeed Low" EICAS caution to inability to trim to autothrottle activation and pitch down, stick-shaker at onset of stall etc. But nothing can protect against laws of physics that apply when there isn't just enough energy for a (possibly) shortened takeoff distance and misconfigured aircraft. Very sad, and bewildering. Subjects: FBW 5 users liked this post.
nolimitholdem 2025-06-12T10:15:00 permalink Post: 11899017	To address a couple points raised as best able: • B787 does have takeoff config warning, but for the flaps will only warn if a valid takeoff flap setting isn't selected - doesn't crosscheck against the FMC, and there is a range of valid settings (UP and 1 are not valid settings) • Similar to Airbus there is LE Autoslat extension for low speed protection. • That EK B777 freighter referenced may have been lightly loaded and generally speaking has far more excess thrust than a B787. Intersection takeoff could be quite valid for the former, having flown both I would be much more hesitant (read: not a chance) to take an intersection in the B787 without an incredibly compelling reason even if the OPT says it's possible. Subjects: Flap Setting Flaps (All) 5 users liked this post.
nolimitholdem 2025-06-12T11:05:00 permalink Post: 11899071	Quote: Originally Posted by Chesty Morgan Can someone tell us the retraction schedule for 787 slats and flaps. I guess similar to the 737 where the slats retract after the flaps...? Correct. The flaps and slats sequence so that the LE slats extend first and retract last. I'm wondering if the takeoff required a Flaps 15 settings but Flaps 5 was set instead in error. Wouldn't be impossible to do, given that the vast majority of takeoffs are Flaps 5 so muscle memory and confirmation bias set in. That wouldn't trigger a config warning, but would leave the a/c in a poor energy state. If indeed an intersection takeoff (which is not confirmed) there'd be zero margin left. Subjects: None 3 users liked this post.
nolimitholdem 2025-06-12T11:14:00 permalink Post: 11899084	Quote: Originally Posted by Gary Parata 787 driver here. The BEFORE TAKEOFF electronic checklist will not show as completed unless the flap position indication agrees with the flap setting entered into the CDU. If that is missed, a CAUTION is issued: CHKLIST INCOMPLETE NORM as the aircraft lines up on the CDU-entered runway. Hmm. B787 pilot also and with respect, on the B787 (-9 tho) in the sim anyway, wanting an answer to this very question we experimented with setting a flap setting other than the one in the CDU and received no config warning. I believe the config warning system reads the flap position sensors, not the CDU. I am completely willing to be corrected but was quite surprised myself. 🤔 Subjects: Flap Setting Flaps (All) 1 user liked this post.
nolimitholdem 2025-06-12T12:41:00 permalink Post: 11899168	Quote: Originally Posted by Kenny 777 guy but you’re talking about two different things. Unless I’m mistaken. You’re talking about the Take Off Config EICAS warning. He’s talking about the Before Take Off checklist showing as complete, if the selected flaps aren’t in agreement with the entered CDU value. Correct. Two different things, sorry if I muddied the water. Also former B777 guy. Would love to go back but that's a different conversation. 😁 Subjects: None 1 user liked this post.
nolimitholdem 2025-06-13T14:15:00 permalink Post: 11900554	Quote: Originally Posted by xetroV Video evidence suggests at least the leading edge devices were extended: https://youtu.be/oUFS2np0mKc?si=0f1Td6bQiqNOE4U- LE devices extended on impact would correspond with the B787 auto-gap function that extends the slats in certain low-speed high AOA conditions for stall protection (aka "Autoslats"). Which this aircraft most certainly was in before impact. Only to say, that LE devices seen extended on the crash a/c don't prove configuration on takeoff. B777/787 rated/current/active pilot. B787 FCOM: Quote: The slat autogap function is only available in primary mode when the slats are in the middle position and the airspeed is below 225 KIAS. At a high angle of attack, autogap fully extends the slats to increase the wing camber, thus increasing the lift and margin to stall. The slats return to the middle position after the angle of attack decreases. The autogap trip threshold is a function of AOA, airspeed and flap position. Last edited by T28B; 13th Jun 2025 at 16:58 . Reason: Formatting assistance Subjects: FCOM Flap Setting Flaps (All) 9 users liked this post.

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