Left wing of 737 from the cabin

In the picture above:

What are the parts numbered "1" and and "3"? Is "2" maybe the reinforcement of the pylon?

  • 4
    $\begingroup$ In the background: London Gatwick Airport's reasonably new skybridge. Fun to walk over and watch airliners taxi beneath you. $\endgroup$
    – Jamiec
    Commented Sep 15, 2015 at 14:45

2 Answers 2


I try to improve on the guesswork of @aeroalias. Here we go:

Parts 1 and 3 are the two exhaust gates on either side of the aft engine fairing, which is part number 2. For a reference, see The Boeing 737 Technical Guide, page 116, by Chris Brady (Google Books link).

The flap actuation mechanism is quite a bit ahead of the flaps, and the same goes for the spoilers.

The engine on the Boeing 737 is placed very close to the wing, so the flaps would sink into the jet blast when lowered to the landing position. This would cause high vibrational and thermal loads on the flaps next to the engine exhaust, especially when the pilot increases thrust in landing configuration for a go-around. To protect the flaps, the exhaust gates were added so this part of the flap does not extend down as much as the rest of the wing flaps.

Boeing 737 flap detail

Drawing of the inboard wing flap of the Boeing 737-300/400/500. The inboard flap track sits within the wing root fairing, and the outer track sits in the aft engine fairing (picture source).


Numbers 1 and 3 are exhaust gates to prevent damage to flaps due to engine exhaust (thanks to Peter Kämpf). Here they are in deployed condition.

737 Exhaust Gates Deployed

Source: britmodeller.com

Number 2 is the flap track fairing. it contains the flap operating mechanism.

The same thing, from bottom:

Flap fairings

Source: www.b737.org.uk

  • $\begingroup$ But in this position there is no flap. $\endgroup$
    – XF-91
    Commented Sep 15, 2015 at 14:49
  • $\begingroup$ The flap is most certainly there, it's just not extended. You can see the flap track within the fairing. The fairing (closest to the plane's body) is white, and has a silver arc cutting through it - that's the flap track. $\endgroup$
    – FreeMan
    Commented Sep 15, 2015 at 15:12
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    $\begingroup$ Well, there's not a flap where the track fairing is, but there are flaps adjacent to it on both sides. The first picture in this answer shows well what it looks like when it's extended. Also, it looks like 1 and 3 are the parts of the flap adjacent to the track fairing. The spoilers are farther forward. $\endgroup$
    – reirab
    Commented Sep 15, 2015 at 15:54
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    $\begingroup$ Would you PLEASE refrain from posting your guesswork when evidence is easy to find online? You were wrong again, -1. $\endgroup$ Commented Sep 15, 2015 at 22:02
  • $\begingroup$ @PeterKämpf Looks like the cutaway I referred was labeled wrongly. Thanks for pointing it out. Corrected the answer. $\endgroup$
    – aeroalias
    Commented Sep 15, 2015 at 22:45

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