ETOPS fuel reserve
 

Taken from Boeing's Aero no 7:

New regulation 14 CFR 121.646 requires that all airplanes flown in extended operations must carry an ETOPS fuel reserve suffcioent to allow flight to an ETOPS alternate airport in the event of these three scenarios:

• A rapid loss of cabin pressure at the most critical point followed by descent to a safe altitude as defined by oxygen availability
• A rapid loss of cabin pressure and a simultaneous engine failure at the most critical point followed by descent to a safe altitude as defined by oxygen availability
• An engine failure at at the most critical point and descent to OEI cruise altitude and diversion at OEI cruise speed

To me it seems scenario "b" is always the limiting one, but I am not ETOPS trained. Can you give an example where either "a" or "c" require more fuel?

FD (the un-real)

Just surmising - it may be that a) COULD be more limiting if two-engine cruise is thirstier than SE cruise at SE speed (at, say, 10,000ft)? I cannot see c) being 'limiting', and nor do I have ANY performance figures to back it up right now.

I'm sure OS and/or JT will be able to answer this one.:)

Just a note that the requirements I quote are probably long standing and not part of the recent LR regulatory change. Also, I wish that apart form OS and JT perhaps m and others will join the think-tank. Maybe there is a historical explanation?

I know that on the good old 757 that it burns more gas at 10,000ft on two engines than it does on just the one... so the two eng decent ETOPS div is most limiting.

TS: Are you referring to equal speeds? I guess 320/737 would also burn less on one-engine, but green dot.

But ETOPS distances would normally be calculated on rather high speeds, correct? For instance the 320 would normally use cca 0.78/290 descent profile, but for ETOPS calculation FCOM suggests strategies of 0.78/320 or 0.80/350 which is VMO! I do not think a twin would consume less on one than on two at 330+ kt IAS. Am I wrong?

FCOM A320:
FL100 LR speed integrated cruise tables:
73-70 tonnes, time to consume 1hr exactly, flown ANM 357. With some simplification this reads 71,5 t, FL 100, IAS 310kt, FF 1500 kg/h/eng.

SE OPS - fixed speed strategies MCT/320kt:
71,5 t, FL100, IAS 317 kt, FF 3153 kg/h
SE OPS - holding at green dot speed:
71,5 t, FL100, IAS 225 kt, FF 2330 kg/h

If you say the 757 behaves differently, I take your word for it but I wanted to make sure we are evaluating the same options.

On the other hand, on a quad, with inboard engine out, I would not be so sure. And if somebody told me that a trimotor with windmilling #2 used less fuel at low level than on three I would have to believe that. Where's a Lockeed expert when you need one?:{

320kts to me (non-Airbii) seems a high speed for SE cruise? Like Rainboe, I would certainly not flog the remaining engine.

For interest, The BAe Lightning was more 'efficient' on one due to the engine operating in a more efficient RPM band, and it was not unknown for those who got themselves on a teeny weeny bit longer piece of string away from base than ideal on a low level detail to 'recover' single-engined.

Our A330's use a single engine cruise speed of 430kts

Rgds

Slow Progress

Yep, the 75 at 400kts (TAS) will burn more on two donkeys than it does on just the one at 10,000ft.

We use 430kts for the 330 too, burns more on one eng tho.

Regards.

400kts rules speed here 757/767/A330

Worst case for us on the 757/767 for us is a 10000ft twin engine, anti-ice on, thirstier over 180 mins than a single engine by about 1.5 tonnes:ooh:

Mutt's probably in the best seat to respond as he has the numbers for a range of aircraft to hand and may be prepared to quote numbers from the calcs.

If it is any help, the ETOPS parameters I use consider the 2 engine case limiting, but I know not of other operators' rules.

I think such reasoning is shared, once the engine has demonstrated to run on MCT/CON indefinitely in a shop, there's no point re-taking the test when airborne over high seas. Same applies for 1 hr take-off alternate case, where the planning limit is also based at approximately 400 kt TAS (737/320).
Obviously, the closer the engine is mounted to the lateral axis, the smaller thrust-line displacement needs to be trimmed-out. The 767/757 data comes as a surprise, however.