Related to this question about plane loading efficiency, if planes have multiple entrances (generally 6 or more) why are planes not loaded from both ends? I think I've seen it happen sometimes, but the majority of my flights are on 737s and are just loaded from the front entrance.
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The aviation industry is already running at near-peak efficiency, performing crucial tasks simultaneously to ensure quick turn-around. Trying to speed up the boarding process by allowing entrance from both ends would be doable with a large amount of changes to the existing process, in both operations and infrastructure. However, the result would be horrendous and time- and resource-consuming at worst and comical at best.
Jetways need to be able to reach all points of ingress/egress, where currently, they only reach the forward doors. Seeing as aircraft nose-in at the gate, to reach the aft doors would require a jetway that goes around the wing (above the wing is even less practical from a design/physics standpoint), effectively creating an even smaller limit to the size of the aircraft that can fit at the terminal since there is now a jetway that needs to reach the rear doors. As you can see, the space between aircraft is already tight:
Or, you use a simple stairway at the aft door and allow passengers on the tarmac, an already busy place during aircraft turn-around, and we don't need them touching anything en route. I highly recommend against the latter.In many instances, during boarding, the rear and/or opposite-side doors are already in use for loading/unloading food and drinks and taking out the trash. So you'd have to redesign that process.
Humans are generally stupid in large groups. Southwest notwithstanding, your typical airline assigns seats. Imagine a passenger entering the rear door with seat 1A. It doesn't have to be that extreme. It can be any seat assignment more forward than another passenger coming the opposite direction down the aisle, which has the effect of halting both directions of travel. Passengers already sit in the wrong seats, or travel with babies, or carry too much luggage (or stow it selfishly).
There have been many studies on efficient boarding methods. The most efficient algorithm seems to be the Steffen Method, but this method requires someone with an inordinate attention to detail (and willing passengers) to line people up in a specific order. Taking into account crew resources, the most efficient method is by window-middle-aisle groups, then by random order (i.e. "single-zone"), with typical "zone boarding" least efficient.
EDIT:
There are scenarios where boarding from both ends makes sense and is feasible, e.g. smaller planes with fewer passengers. On larger aircraft, the problem compounds itself as the number of passengers grows, each "collision" incident affecting that many more people in the queue. Minimizing collisions requires airlines to throw more resources at the problem, namely personnel to direct traffic. Ask any CFO - more often than not, human resources is the most significant slice of the operating budget.
In any case, engineering a solution should not entail best-case scenarios; it should be designed for typical-case at best, and more commonly for worst-case. The human factor is one that cannot be overlooked. There is no such thing as an idiot-proof system.
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2Also keep in mind that any jetway has to get out of the way for the plane to move in or out of the gate, which takes up even more tarmac space around where people are working on the plane next to the one leaving. – cpast Feb 02 '15 at 04:10
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4cost-prohibitive. digging up the ground (tunneling) is monumentally more expensive than building a bridge. – Erich Feb 02 '15 at 06:07
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Well, there is always somebody at the gate who checks the boarding cards and can direct the passengers to the right corridor. If bus and stairs are used, there often are two stairs and the flight attendants sometimes stand by the bus and direct people like that. – Jan Hudec Feb 02 '15 at 08:35
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2"Imagine a passenger entering the rear door with seat 1A." - two boarding zones. Front passengers (1 to 15) and back (16 and higher). – Dan Dascalescu Feb 02 '15 at 09:19
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8what you describe is a perfect scenario. someone will board from the wrong door. – Erich Feb 02 '15 at 09:58
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4I have often seen boarding happening from both ends, front and back on smaller aircraft's at airports with bus boarding. Usually security at the front will allow in only rows 1-15 and at the back 16 onwards. (they will stop you before you climb the stairs) – Akash Feb 02 '15 at 11:29
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not surprising and easily doable due to the small pax count. i haven't run any numbers, but i imagine that time spent in boarding scales at best O(n^2) for n passengers. any algorithm for more-efficient boarding needs to consider not only time, but crew workload as well, which is why dr. steffen's method is unrealistic. – Erich Feb 02 '15 at 13:36
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EasyJet A319/A320 planes in Prague Vaclav Havel (PRG) are usually unloaded using the bridge, but loaded through the bridge only until row 15, people sitting in row 16 and behind and sent on the tarmac and loaded through the moving stairs in the back door. The reason they seem to give is not that it's faster to get on the plane, but it's faster for all the people to organize themselves, put the baggage where it belongs, sit down, etc. They rarely refuel or do more-than-necessary maintenance in PRG, so loading the passengers is a limiting factor, as well, there's enough space on the tarmac. – yo' Feb 02 '15 at 14:43
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@JonStory One of the plane's routes is LUT-PRG-CDG (LUT is EasyJet's base) and I'm sure that once I observed the plane from gate arrival until I loaded myself into the plane some 15 minutes before pull-out, and I didn't see any tanker on my side of the left side of the plane (I can't 100% speak about the right side). Both legs are very short, so I suppose they get fuel at home for both legs at better price. – yo' Feb 02 '15 at 14:59
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Dulles (outside Washington DC) at one point intended to have passengers loaded via "mobile lounges" [buses with scissor lifts]. I would guess that if planes didn't need to load and unload other cargo, such a design could improve turnaround time, but as it is planes overlap the time they spend loading/unloading passengers with time spent doing other necessary tasks. – supercat Feb 02 '15 at 17:02
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1Typical "zone boarding" does not occur in real life because passengers do not line up in order like robots. Random boarding did pretty well, and is the one passengers prefer because they get to do what they want. I expect that adding in a moderate amount of rear-to-front bias is an improvement on random boarding, which is precisely the boarding scheme the airline achieves by asking people to board in zones. – Level River St Feb 02 '15 at 22:29
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@erich People in the rear boarding from the front door (because they aren't familiar with the new boarding procedures) won't make it any slower than the current system. People in the front are unlikely to board from the rear door, because people are lazy and that would mean walking farther. – user253751 Feb 02 '15 at 23:22
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3@immibis People in the rear boarding from the front door will cause headaches. Suppose the aircraft has 30 rows and I'm sitting in 23C. I head to the rear door and board from there. Another passenger in 28F has boarded via the front door. We're standing in the aisle blocking each other, and passing in a narrow aisle when we both have roller bags is challenging at best. Meanwhile everyone else is stuck in both directions. – Zach Lipton Feb 02 '15 at 23:41
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3It's worth noting that while the rest of the operations on the tarmac and at the terminal may be near "peak efficiency" the process of boarding the aircraft is *empirically* about as inefficient as we can make it (see here from Bloomberg Business, this delightful Mythbusters segment). – voretaq7 Feb 03 '15 at 01:56
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1@voretaq7: as a sum of all parts. also see peter's response noting that it's not much worth it to speed up one process (boarding) only to still wait on the other processes to finish. – Erich Feb 03 '15 at 02:05
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Regarding the Steffen method, it doesn't really actually require anyone with an inordinate attention to detail. It only requires a computer with inordinate attention to detail (which is easy for a computer) to assign boarding positions based on the Steffen method and then something like what Southwest already uses to get people to actually line up in that order. In my experience, this seems to work reasonably well for Southwest. It's much more orderly than Delta's boarding process where many people don't seem to understand that Zone 1 is actually the third boarding zone. – reirab Jun 04 '15 at 14:42
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@voretaq7: The mythbusters experiment used the same passengers every time. If they didn't shuffle the seat assignments every time, people would start to make local optimizations. Also, getting your plane-boarding skills warmed up in general will probably speed later runs, as you've already figured out exactly how your bags fit in overhead bins. I bet a 2nd run of zone boarding would also have been faster than their "control", even if they did reshuffle seat assignments. No idea whether this would have been enough to make it faster or more pleasant than any of the other methods. – Peter Cordes Sep 23 '15 at 20:49
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I don't know the physics involved. Is the entire process free from regulatory oversight? The cognizant regulator (if there is one) turns a blind eye to the boading/deboarding of passengers and lets the chips fall where they may? Or do the regulators get involved with how things need to be done? – Gayot Fow Sep 24 '15 at 00:31
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I'm not sure, but I think this is somewhat a geometry thing. If planes are being loaded from a jetbridge, it would have to get past the wing to reach the rear door. That would involve it having to drive around the wing to get to the door, which is somewhat space-intensive, and also requires a pretty long jetway with limited ability to have supports along its length (since it has to deal with different wing sizes). On planes with multiple front doors along one side, it's not that uncommon to see them being used, whether they're on different levels or there's just a door at the front and another door in front of the wing. There, it's just a matter of how many jetways the airport has at the gate, but they don't have to drive around the wing.
When planes are being loaded or unloaded away from the airport, it's not uncommon to load/unload from the back as well as the front; there, they just have to use two mobile lounges (at IAD) or airstairs (just about anywhere else).
cpast
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This is the primary answer. We like jetways and getting a jetway around the wing is not feasible while parking aircraft perpendicular to the terminal. Parking parallel to the terminal would both be difficult to maneuver and take up too much space per aircraft. If you want a really good idea of how dense aircraft parking at terminals can be, take a look at Atlanta. – reirab Feb 02 '15 at 14:38
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4Atlanta should never be used as an example, on account of the fact it's an inherently silly airport with an underground train. The sooner Hartsfield-Jackson accepts that it's a theme park, not an airport, the better. – Jon Story Feb 02 '15 at 16:40
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Some lowcost airlines use both ends to speed up both loading and unloading the passengers. Moreover, for huge aircrafts (A380 and B747), you may use several jetways
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3This is always done with two stairs, (not a jetway and a staircase) and generally away from the terminal building to avoid congestion at the jetways. I suspect that, besides the increased height, larger planes have increased probability of a disabled passenger, which would make stairs not an option. – Level River St Feb 02 '15 at 17:35
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@steveverrill Yes, having more passengers increases the probability that you have one who can't use stairs. But boarding by stairs is, as Jon Story says, very common for European budget airlines and they must have some method of getting people who can't use stairs onto the plane. – David Richerby Feb 02 '15 at 18:38
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@steveverrill: as a side note I had a few cases where the passengers were leaving the plane via the jetway and stairs (and meeting at the top of the tower - the stairs ones needed to climb up) – WoJ Feb 03 '15 at 12:08
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1@DavidRicherby, there are mobile lifts that are used for disabled passengers. – Ian Ringrose Feb 03 '15 at 16:45
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@steveverrill I think the question is not restricted to jetways. I've already seen passengers boarding via jetways whereas other board via stairs at the same time (it was in Spain, I should have taken photos to illustrate my answer). And yes, it was on a European budget airline. – Manu H Apr 08 '15 at 09:48
At most airports with jetways, boarding occurs from at least the second floor of the terminal building. That means that passengers who take stairs down from a rear exit would have to climb back up into the terminal, which is inconvenient.
– Zach Lipton Feb 02 '15 at 03:45