All excellent information.

Regarding flaps for departure, sometimes the settings may change between pushback, initial settings, and take-off.

Example: Rush Hour at JFK and there are thunderstorms in the area. Most folks on here have likely experienced the JFK madness I speak of.

There are twenty aircraft in line for takeoff on a taxiway adjacent to the active departure runway. The first six planes on the taxiway leading to the start of the runway cannot depart because ATC just closed Robbinsville.

These a/c either need to wait or request re-routes from JFK ground/clearance delivery.

Aircraft #7 is flying a different route. The numbers have been run, meaning all the take-off computations (weight, runway length, density altitude, winds, etc), and the flaps set for the appropriate setting.

Kennedy Tower wants to keep things moving - and I must add they do a damn good job - even though it may not seem like it as a passenger at times. Kennedy Tower calls a/c #7 and asks if it can depart from the intersection of taxiway Kilo and the runway.

The numbers are run to see if it is possible to depart with the current settings from the intersection of kilo. There is considerably less runway departing from here and it may require a change in take-off settings (including flaps).

Pilot either advises the tower "no" or decides the #'s are fine (or makes an adjustment) and then advises the tower yes they can depart.

JFK Tower then tells a/c #7 to taxi into position at Kilo on Runway XX. The tower then clears it for departure. Up and away #7 in line goes while six aircraft are waiting ahead.

In the meantime a/c #8 (now #7) in line is in the same position and departs from kilo. Then a/c #4 gets a re-route, but can only enter the runway at the echo intersect. #4 then goes up, up, and away. #10 can also go, but #9 is going to PHL which is on a ground-stop. #9 moves out of the way, powers down to conserve fuel, and lets #10 go by to depart at the kilo intersect.

The tower keeps tabs of who is in line and keeps things moving. When conditions are like this, often last minute adjustments need to be made.

Just adding more information here for those who are interested.

To add onto what TrayFlowInUK said the flaps on some planes are enormous when deployed on landing. Unless you're sitting at a window seat on the wing, I suspect a lot of people don't even realize how far they extend on some planes like the 747. It'll be interesting to see the A380 if and when Qantas takes delivery and puts them on US routes.