The following is from a captain who flies the A380:
The Air France A380 which suffered an engine failure is to be flown back with only 3 operating engines. Some notes about how that is done..
The operating crew have to have completed a special training course. They also have to complete a simulator session prior to actually conducting a 3-engine ferry flight in order to practice the required handling techniques and operational items. If possible, this simulator detail will match the actual weather conditions, aircraft state, and airports as closely as possible.
One extremely important consideration is the failure of an engine, leaving the A380 powered by only two engines. Therefore, the aircraft weight will be low. Obviously no passengers or freight are allowed!
The inoperative engine must be configured in one of two states. Either windmilling or have had the core removed. Note that the inoperative engine cannot be missing completely. Therefore, in some cases, the previously damaged engine may be removed and replaced by another which is left to windmill rather than supplying power. If an engine is to be allowed to windmill, consideration must be made as to whether the lubrication system is available. If not, maximum flight time is 7 hours.
The route flown must ensure the aircraft is never more than 240 minutes at 2-engine inoperative cruise speed from a suitable airfield.
The takeoff performance application usually used to calculate takeoff data can be run in a special 3-engine ferry flight configuration.
A speed termed Vstop is calculated. This is the speed to which the aircraft can be accelerated with 3 engines operating and still brought to a full stop within the accelerate-stop distance available. At or above Vstop, in the event of an engine failure, the aircraft must continue the takeoff.
Takeoff can be carried out on a dry or wet runway, but not a contaminated one. Maximum crosswind for takeoff is 10 knots. Takeoff configuration is always 1*F.
The engines must not be used to provide bleed air during takeoff.
TOGA (max) thrust on the operating engines must be used for takeoff.
At the start of the takeoff, the aircraft is positioned 5m to the side of the runway centreline on the side of the two operating engines.
There is a set procedure for accelerating the engines in a different way to a normal takeoff due to the thrust asymmetry. This varies depending whether it is an inner or outer engine which is inoperative.
Recommended speeds in flight are 250 knots below 10000 feet (if ATC require this). 300 knots above 10000 feet until Mach 0.79 is reached, then cruise at M0.79. Similar speeds in descent.