747 Questions

[TightSlot]

Please excuse questions from an F/A (and adjust your answers accordingly!)

I've been following the BA747 3 engine LAX-LHR article (http://www.pprune.org/forums/showthread.php?t=220109) in R&N with idle interest, and have realized that I don't know enough to form an opinion: However, I do have a couple of questions wandering around my purty little head...

If an engine fails, is there some way of locking it from the flight deck, or does it continue to spin until after landing (just as the fan blades spin in a high wind on the ground)
Would a locked engine burn more or less fuel than an engine with spinning fan blades?
If the fan blades spin in the air at cruising speed, does the engine still deliver a (small) amount of thrust that might be useful, or is it just dead weight?
Whatever the answers to 1 - 3 above, does the FMC know the correct answers, and adjust accordingly?Thanks in anticipation.

[Dan Winterland]

1. No. But if you are going to ferry an aircraft with an engine out, the usual procedure is to stop the fan rotaing prior to departure.

2. Don't know, but I suspect there is no difference.

3. No. It will all be dead weight, but more importantly, drag. However, a windmilling engine may give you the benefit of some hydraullic pressure but probably not electrical power. In a 747, the failed engine's hyd system will be maintained by the Aux pump which is either air or elcetrically driven depending on which engine.

4. The FMC has an engine out prompt. Press this, it will tell you your new maximum and recommended altitudes, you new cruise speeds and calculate the new fuel burn.

[TopBunk]

1. No, we can't 'lock' it so it continues to windmill
2. Less than a locked fan - much less, and with much less drag, locked = bad
3. Thrust is produced by burning fuel, there is no fuel being burnt, so no thrust
4. You select 'Engine Out Mode' in the FMC, it then can provide accurate fuel predictions, achievable altitudes, etc

HTH

[TightSlot]

Wow! - speedy response - many thanks.