View Full Version : EO critical alternate fuel
wingtip777
14th Nov 2002, 01:48
hi
anybody heard EO(engine out) critical alternate fuel? what is it? how to calculate it?
thanks a lot !;)
We calculate EO critical fuel scenarios for ETOPS, is this what you mean?
Mutt.
wingtip777
14th Nov 2002, 06:14
yes, MUTT. please tell me more or tell me where to find information about it! thank you very much!
captchunder
14th Nov 2002, 09:52
Take a standard flight from East coast US to UK, and your en-route alternates can become slightly limited mid atlantic. Lets say Gander and Shannon are suitable alternates for your ETOPS flight (weather and facilities OK). You will therefore have a point along the route where the flying time is equal, taking into account winds, to fly back to Gander or on to Shannon. This is called the critical point, as here you are furthest away (time wise) from a suitable alternate.
Under ETOPS rules, you have to cover the worst case scenario that you would be able to do something about, which would be an engine failure with simultaneous decompression at the critical point. Obviously, flying a long way at 10000ft (in assumed icing conditions) is going to eat through your fuel reserves.
If the flight planning computer calculates that extra fuel would need to be carried just to satisfy this scenario over and above that which you would have in the tanks at that stage, then that is annotated on the flight plan as critical fuel. It is usually as a result of the decompression part of the equation rather than the engine fail.
Normally, however, you have the availability of some more en route alternates (Keflavik, Lajes) so that the requirement to lug around extra fuel which you are highly unlikely to need reduces to nothing.
Hope this (very general) example gives you an answer
Fresca
14th Nov 2002, 12:33
captchunder:
I always thought that 3 scenarios must be check out. One is when there is an engine failure and then is there the driftdown to max EO alt. and then to ETOPS alternate. Second, as you pointed out is and engine failure with decompression and from there to an alternate at 10.000'. The third, (which is always the most limiting fuel wise for us any way,) is just decompression and from there to an alternate at 10.000'.
For a 757 from an island in the Atlantic to the East Coast of the USA, it is worse fuel wise to lose pressure than it is to lose an engine and pressure.
Best regards