Reading this question I saw this picture in MikeFoxtrot's answer and noticed how easier it would be to board the plane using that huge door:

enter image description here

I understand that for single aisle planes you wold need to form a single line anyway, but for two aisle planes having a wide door could speed up the boarding process a lot.

So, is there a reason why it is not done? What is the limiting factor in the door size?

  • $\begingroup$ Note, too, that there is the large cargo door, used for loading the seats, and the smaller passenger door right in front of it, used for loading the seats' cargo. Imagine walking up a set of stairs to the gaping hole in the side of the plane, only to be confronted by 4 rows of chairs - you think getting on a plane takes a long time now! $\endgroup$ – FreeMan Apr 7 '15 at 14:07
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    $\begingroup$ Great, a bigger door to wait in while people cram their luggage into the overhead bins and squeeze into the economy seats. $\endgroup$ – fooot Apr 7 '15 at 14:36
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    $\begingroup$ Regarding the logistical reasons for not using larger doors. $\endgroup$ – fooot Apr 7 '15 at 14:43
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    $\begingroup$ I think you will find that the bottleneck in the boarding process is not the door, but further down the aisle about row 14 where a small person is attempting to earn an Olympic Medal for his/her weight class by stuffing all his/her worldly possessions into the overhead storage compartment. $\endgroup$ – Skip Miller Apr 7 '15 at 16:04
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    $\begingroup$ Or 2 people arguing endlessly with everyone else about wanting to sit together in seats that are completely different from the ones assigned to them, until a flight attendant manages to push herself 25 rows aft and negotiates a solution ten minutes later. $\endgroup$ – jwenting Apr 8 '15 at 3:46

Multi-aisle commercial aircraft adopt a multi-door boarding strategy rather than a single-huge door (see the A380 or the B747, both use two doors). This helps under the structural viewpoint: the presence of a door (cargo or passenger that might be) induces design problems that are amplified if the compartment has to be pressurised.

A door interrupts both frames and stringers and weakens the overall aircraft structure. A huge door interrupts many more frames than a small one and two small ones can be set apart from each other to have some continuous frames between the two, restoring some rigidity.

The complex closure systems ensure that part of the stresses are carried by the door material, but it will never be perfectly transmitted as it would be without a door. As mentioned before, the stresses are heightened if the compartment is pressurised (as when passengers have to be transported).

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    $\begingroup$ A small comment here: A380 can use upto 3 doors if airport is equipped. $\endgroup$ – vasin1987 Apr 8 '15 at 7:41
  • $\begingroup$ Actually, the aircraft doesn't even have to be multi-aisle to use two boarding doors. Some airports/airlines do that with 757s, for example. All you need to do this is an aircraft with at least 2 doors in front of the wing, though that does generally exclude most aircraft smaller than the 757. In the case of single-aisle planes boarding with 2 doors, the first door is usually used for boarding first class and the other used for boarding economy. $\endgroup$ – reirab Jul 14 '15 at 13:32
  • $\begingroup$ also, some airlines at some airports in the states use a front and back door. Some 737s (Southwest, if I recall) are loaded from both front and back at SJC and BUR. $\endgroup$ – Peter Feb 29 '16 at 21:01
  • $\begingroup$ @vasin1987 Why only 3 doors? Doesn't A380 have like 8 doors? $\endgroup$ – Firee Mar 23 '17 at 6:56
  • $\begingroup$ @Firee three doors are used for normal passenger loading/unloading. The other thirteen doors are used by passengers only in emergency. Normally they are used to service galley, loading food carts etc. $\endgroup$ – vasin1987 Mar 23 '17 at 7:10

Before answering your question, please take a look at the excellent answer to Why aren't planes loaded from both ends?, which talks about increasing efficiency in boarding passengers.

Airliners do not need bigger doors for boarding people because people are not like big crates which are loaded into airplanes using forklifts.

To incorporate a wider door, we need to do the following:

  • have a bigger foyer inside the door

    All space on a passenger airplane is fully utilized to the maximum extent. Having a large area just to greet passengers and help them to their seats is not a very efficient use of that space.

  • size of jet bridge

    New jet bridges will be needed, which can allow more than two people walk side-by-side.

  • gate procedures

    Most of the airlines have designated their seats into zones1. When boarding, people are called in a manner which expedites the boarding process. With a bigger door, this process needs to be adjusted for boarding more people at the same time.

At present, only A380 has an upper deck for passengers, which extends the length of the aircraft. They already have multiple jet bridges to maximize the boarding process:

A380 Jet Bridge
Image Source

1: Not talking about travel classes.

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    $\begingroup$ Why not just have it open into the bar/lounge/lobby? $\endgroup$ – fooot Apr 7 '15 at 14:52
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    $\begingroup$ @fooot The bar/lounge/lobby isn't on every A380, and not on both levels. I think it might not of on all A380s of a specific airline either. $\endgroup$ – Farhan Apr 7 '15 at 15:02
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    $\begingroup$ I'm actually not certain that the boarding zones really have anything to do with your seat location on the aircraft. At least on Delta (the only airline I commonly fly that has boarding zones,) these are mostly just assigned by your status with the airline and/or when you checked in. It seems to be more for allowing frequent fliers or those who have paid for better seats or priority boarding to have first access to the overhead bins and managing the flood of people rushing the gate at the beginning of boarding than for actually loading the plane efficiently. $\endgroup$ – reirab Jul 14 '15 at 13:38
  • $\begingroup$ "...because people are not like big crates which are loaded into airplanes using forklifts." What if you had the passengers board the seats outside the aircraft, and then forklifted the blocks of seats in? $\endgroup$ – Sean Mar 14 '19 at 0:06

A door involves reinforcement of the structure around it (on the fuselage), so a bigger door involves more structural reinforcement, which means it adds more weight (because of the beefier structural reinforcement). In airplane, whatever you do, you want to keep the weight of the structure as low as possible, so you can carry more people. It's economic reason (the airline is a business). Technically windows need structural reinforcement as well, but without window it would be boring, and probably less people would fly (they would feel less safe to not see outside).

The cabin is pressurized, so the bigger the door, the more pressure pushing to pop it open (which is why it would need beefier structural reinforcement)

  • $\begingroup$ Airliner doors generally open inward. Pressure from the inside won't pop them open, at least not without ah... major structural failures. $\endgroup$ – T.J.L. Jan 15 '19 at 15:13

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