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Almost all narrowbody jetliners, and many widebodies as well, use overwing exits to augment their evacuation capabilities; to escape the aircraft, a passenger or crewmember in the exit row pops the hatch next to their seat, and then everyone else1 chases them out onto the wing.

At this point, depending on the aircraft, they may simply slide down the flaps to safety, or a slide might inflate if the wings are too high above the ground. Either way, though, they’ll be going over the trailing edge of the wings if it’s a land evacuation;2 even if the aircraft has multiple overwing exits per side (common among the larger jetliners), or if there’s a tail-mounted engine waiting to gobble up trailing-edge evacuees (like with the Fokker 70), everyone going out on the wings still evacuates off the trailing edge.

I know of only a few airliners with overwing exits that specifically direct evacuees over the leading edge of the wings, and two of these are very special cases:

  • The Concorde’s wings extend for most of the length of its fuselage, so it would be essentially impossible to fit enough exits in without having some going over the leading edge.
  • The Il-62 has a set of engines so close behind the wings that even the emergency-exit designers realised it would be a bad idea to send evacuees over the trailing edge (also, its overwing exits don’t have slides - instead, you have to slide down a rope over the leading edge of the wing).
  • The DC-10/MD-11 family has overwing evacuation slides that go over the leading edge of the wing, as do some A310s, making these, so far as I am aware, the only subsonic airliners without engines right behind the wings to use leading-edge overwing exits.

For low-slung narrowbodies, where you slide down the flaps to get to the ground, the predominance of trailing-edge overwing exits is excusable, as the flaps are on the trailing edge of the wing; however, even for large narrowbodies and widebodies with inflatable overwing evacuation slides, the slides still overwhelmingly open rearwards, over the trailing edge.

Why are overwing exit slides leading off the trailing edge of the wings so much more common than ones that go out over the leading edge?


1: I exaggerate slightly; some of the passengers will likely lock themselves in the lavatories or run up and down the aisle(s) screaming like chickens with their heads cut off, and one or two might even use the exit doors at the front and/or rear of the plane.

2: Ditchings work somewhat differently, and some aircraft do call for occupants to fall off the leading, rather than trailing, edge in this case.

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  • $\begingroup$ Why would you expect engines to be running during evacuations? One would think that they either stopped of their own accord or as a consequence of the crash (which might be why you're evacuating :-)), or the pilots would have shut them down. $\endgroup$
    – jamesqf
    Jan 16 at 17:17
  • $\begingroup$ @jamesqf: Maybe there's something that keeps the engines from being shut down (for instance, if the engine-control cables were severed by a rotor burst in one engine or a break in the fuselage). Maybe the evacuation was initiated from the cabin and the pilots only find out about it (and start the engine-shutdown process, which takes time) when the exits pop open and illuminate the O/W EXIT lights in the cockpit. $\endgroup$
    – Vikki
    Jan 16 at 21:23
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    $\begingroup$ While they likely aren't running, engines are likely to be a high risk for fire location, so I think it's reasonable to raise eyebrows at exit slides that delivery people in their proximity. At any rate, I think the question is interesting enough to have merit with or without the digression about engine location. $\endgroup$
    – CCTO
    Jan 16 at 23:30
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    $\begingroup$ The trailing edge is closer to the ground, so evacuation there is less dangerous. $\endgroup$ Feb 20 at 0:51
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The special cases you listed (minus the very special case Concorde) hold the clue.

The Il-62, DC-10, and MD-11 are all tail-heavy due to the tail-mounted engine(s).

The emergency exits are designed inside-out, not outside-in, meaning, the locations are not only dictated by each exit's size, but by the cabin's seating arrangement first.

(e) Uniformity. Exits must be distributed as uniformly as practical, taking into account passenger seat distribution.
(...)
(4) For an airplane that is required to have more than one passenger emergency exit for each side of the fuselage, no passenger emergency exit shall be more than 60 feet from any adjacent passenger emergency exit on the same side of the same deck of the fuselage, as measured parallel to the airplane's longitudinal axis between the nearest exit edges. (14 CFR § 25.807)

The tail-heavy examples by design have the main wing more aft, leading to that scenario. The rest, the opposite.

The DC-9 extended family[a] is more special, as there's an exit in the tail (also usable for entry):

enter image description here
Source: aircollection.org

And with the floor-level exits right ahead of the engines being not full-size (compared to the forward doors), it's been balanced that way. Otherwise it would have used an exit arrangement similar to the Il-62's, or the Vickers VC10 with a large exit forward of the wing in some configs, and/or over-the-leading-edge overwing exits in others:

enter image description here
Different VC10 configs; sources: wikimedia.org and wikimedia.org

The A310's reason is the original A300 fuselage that was shortened. If there are other configs, it would be related to passenger capacity.


a: optional on DC-9, standard on MD-80/90, removed from B717[1]

1: Becher, Thomas. Douglas Twinjets: DC-9, MD-80, MD-90 and Boeing 717. Crowood, 2002.

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  • $\begingroup$ Let us continue this discussion in chat. $\endgroup$
    – Vikki
    Mar 27 at 20:38
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    $\begingroup$ I imagine the OP said this in the discussion that got moved to chat, but I don't see how the location of the other emergency exits makes a difference whether the passengers are directed to jump off the leading edge or the trailing edge of the wing. The CFR snippet you quote seems to influence the location of the emergency door, but not the painted markings that direct passengers which side of the wing to jump off. $\endgroup$
    – rclocher3
    Mar 31 at 2:59
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    $\begingroup$ @rclocher3: CFR snippet plus wing position results in different shortest paths for the emergency slides in the examples noted in the question. Note that the arrows are not really compulsory, e.g. in a nose landing gear collapse, sliding forward will probably be better even if the arrows are rearward, unless instructed otherwise of course. $\endgroup$
    – ymb1
    Mar 31 at 15:12

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