I don't think the time taken for refueling, etc is the limiting factor. There are a couple sequences of events that need to happen (simultaneously) to get the plane ready to leave.
Sequence 1: allow arriving passengers to deplane, then clean the plane, board new passengers
Sequence 2: Refueling, other maintenance
Sequence 3: load checked baggage
The time taken to ready the plane is the maximum of the times for the 3 sequences above. It seems refueling takes less than 30 minutes (http://answers.yahoo.com/question/?qid=20061018151916AAMkss8), and I'd guess the checked luggage can be loaded within 30 minutes as well.
I'm inclined to believe that deplaning, then cleaning, then boarding new passengers takes longer than 30 minutes, and boarding passengers IS indeed a bottleneck (unless there are special circumstances like deicing at the gate).
Boarding passengers takes less than 20 minutes in most cases. Even with very fast airlines like easyjet, the plane sits longer the passengers board.
Also, you know that airports queue planes, right? So a plane can't just hurry up to fill in passengers and take off.
And in any case, why? Let's say you saved enough time to make an extra trip in a single day, then it would be worth it, but this is not going to save it. So you finish your pilots workday 20 minutes earlier, this is no saving. And if you are pushing your planes that hard anyways, there is no time for proper plane maintenance and checkups.
I've done a lot of short trips within Europe by plane, and I've never observed boarding time to be an important factor.
In 3 of the last 4 flights I've taken, boarding was the limiting factor. We left the gate within 5 minutes after the last person boarded, and were airborne shortly after without having to wait on the tarmac. On one of those flights, the plane didn't finish boarding until 10-15 minutes after it was scheduled to take off.
Curiously, the one exception was a United red-eye back from SF to Boston. And I think they may've been using this boarding method - the gate attendants said that the boarding groups were window seats first, then middle, then aisle. There certainly was no rhyme or reason to seating within boarding groups, and there were about 12 boarding groups.
But when did you start boarding? When did the planes arrive? They usually make you start boarding about 20 minutes before they are allowed to take off, so people sit in the plane the minimum amount of time.
Planes usually arrived about 40-45 minutes, sometimes up to an hour before we started boarding.
In 2 of the 3 flights, that might've been the case. But that other one, we were actually late, so I don't think they delayed boarding so we wouldn't have to wait. Actually, we started boarding about 15-20 minutes after we were scheduled to start boarding.
Cleaning seems like the real bottleneck, but assuming they can't get the flight attendants to work any faster, any time saved on boarding shortens the deplane/clean/board cycle.
If the pilot finishes 20 minutes sooner as a stable number you can send out a new pilot and keep going or reduce airspeed and save fuel. If nothing else you can have a large cushion so delays don't propagate though the day. AKA your 10 min late at 10 am and your still 10 min late at 10pm. I suspect most large airplanes fly fairly complex routes so you can consider 30 min a day as 1 / 50th of a virtual airplane if you change which route each plane takes.
> "Also, you know that airports queue planes, right?"
Yeah, but usually a queued plane is waiting on the tarmac, not at the gate, right? Fixing boarding delays may not always lead to earlier takeoffs, but it can definitely get planes pushed out of the gate faster (freeing that gate for other planes).
Also, boarding time probably depends a lot on the type of plane (ie, even more so than fueling time does). I fly trans-Atlantic every now and then -- boarding a 747 full of people who don't fly regularly almost always takes more than 30 minutes.
Maybe boarding time isn't a delay for small planes, but I'd bet it is for big planes.
If you fly transatlantic, then those planes require more than an hour on the ground before flight. And planes get queue times allocated as soon as possible and pre-planned, not just when they leave.
But it really doesn't matter. Most flights will finished boarding well before the departure time, and many will arrive late as they always do. The plane can't leave until the departure time, so unless there's a direct cost benefit, why bother?
They load so early because they have to guarantee that everything can happen in time. If you can reduce the time it takes to board, you can board passengers closer to the actual departure time. This allows you to squeeze flights closer together, which saves a ton of money.
Sequence 1: allow arriving passengers to deplane, then clean the plane, board new passengers
Sequence 2: Refueling, other maintenance
Sequence 3: load checked baggage
The time taken to ready the plane is the maximum of the times for the 3 sequences above. It seems refueling takes less than 30 minutes (http://answers.yahoo.com/question/?qid=20061018151916AAMkss8), and I'd guess the checked luggage can be loaded within 30 minutes as well.
I'm inclined to believe that deplaning, then cleaning, then boarding new passengers takes longer than 30 minutes, and boarding passengers IS indeed a bottleneck (unless there are special circumstances like deicing at the gate).