I noticed this particular portion of the flaps moving differently from rest of the wings. In the attached picture, the middle flap is raised. Is this considered normal?

The landing and takeoff in this flight was normal, but the flaps moving like this made me a little (lot) uncomfortable! I've added a video, as well.

weird flaps

Video on Youtube

  • $\begingroup$ Related $\endgroup$
    – Pondlife
    Mar 24, 2017 at 12:49
  • $\begingroup$ How can this be a duplicate? The other question is answered by explaining why there is a gap in the flaps, and how (and why) this inner "high-speed aileron" (flaperon) is used at high speed when the regular outer aileron is locked. It doesn't at all answer what happens at low speed. $\endgroup$
    – mins
    Mar 24, 2017 at 17:45

1 Answer 1


I believe the engine is mounted in front of that part.

This means that if the part moved along with the rest of the spoiler the jetblast would be deflected down which will create an upward force on the wing. You don't want that while you have full spoiler deployment.

Putting a gap in the spoiler will reduce stress on the full spoiler from the jet blast. This leads to less expensive maintenance as the stresses are reduced mostly to a single panel and its attachment points.

As @Ron points out the flap geometry is such that you can't have the full flaps adjacent to each other without them jamming up when they deflect. Putting an extra panel between them lets it move on top of the other 2 flaps when necessary.

  • $\begingroup$ It's a Boeing 787-8, if that helps? I found this picture of the plane and it looks like you're right about engine being mounted in front of the part there: i.ytimg.com/vi/a2GlO16qiIA/maxresdefault.jpg $\endgroup$ Mar 24, 2017 at 11:19
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    $\begingroup$ The engine isn't there, but look at the wing geometry. That panel can't lower because it would jam the flaps on either side. So they made it a spoiler $\endgroup$
    – Ron Beyer
    Mar 24, 2017 at 11:23
  • $\begingroup$ As noted by @Pondlife, that's not a flap but an aileron, that's why it's not moving like the flaps. See aviation.stackexchange.com/a/8905/1031 for more details. $\endgroup$
    – Albireo
    Mar 24, 2017 at 14:11
  • $\begingroup$ @Albireo It is a flaperon. Labeling it as merely an aileron is incorrect, as is labeling it "not a flap". $\endgroup$
    – J W
    Mar 24, 2017 at 14:30
  • $\begingroup$ All the comments saying it can't lower didn't bother to watch the video attached to the question - which shows the part lower - even below the other parts at some points. The statement that it will jam is shown clearly to be inaccurate. $\endgroup$ May 6, 2017 at 10:39

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