777 Inflight autostart behaviour - Dual Eng Fail/Stall

[STBYRUD]

Hello everyone,
during a recent sim session we had time to spare and tried a dual engine flameout below 10,000ft in relative vicinity to an airport. Memory items were accomplished, the checklist was read from paper as the APU started, we decided not to speed up to 270KIAS but instead to directly go in for a landing. When the APU came online though I wondered why the checklist does not even offer the possibility to start at least one engine using APU bleed air... in the debrief I brought that up, the instructor claimed that the sim didn't reflect the autostart behaviour correctly - the actual airplane would assist the start with bleed air as soon as it would be available from the APU without further switching. Re-reading FCOM/FCTM and even the AMM SDS I couldn't find any evidence of this. The AMM is clearest and basically states that the starter will only run when the start switch is in START.
Two questions:
- Does the airplane indeed behave differently than this simulator did (engines windmilled without an increase in N2 after the APU came online)
- Why does the checklist omit the possibility to use the starter? (maybe because the subsequent ENG FAIL L/R does?...:sad:)

I know this is a very hypothetical question, a windmill start at 270 knots is usually the best course of action - but if for some reason you cannot dive down to attain 270KIAS (due to high terrain during the initial approach perhaps) there should be an alternative.

Thanks!

[Dog watch]

I'm assuming you were in a GE powered model re the 270kts, Rollers being 250kts.

The inflight start envelope (above FL220-APU bleed not available) will only offer a windmill start unless bleed air is available from other engine(not in your case).

Once speed is reduced below 270kts GE ,250kts Rollers, you will notice a magenta XB OR XBLD ( depending on blockpoint) above the starting turbine, in your case the N2.

Once this is displayed the checklist will guide you to use bleed air to assist start.

I've seen what you describing before and it tends to happen because while actioning the checklist, when the statement, 'is XB or XBLD shown' the speed bubbles up and down a knot or 2 above 270GE/250RR hence no longer displaying XB/XBLD.

Everytime I've used this in the sim the relight/s have been text book.

In short if bleed air is available and a windmill start is not working , then change your plan. Just put the start selector in start and try that. Better than the inevitable dead stick forced lob.

[CharterJake]

- Does the airplane indeed behave differently than this simulator did (engines windmilled without an increase in N2 after the APU came online)

Well, my two cents worth...
Yes, the airplane is the airplane and the box is just that! The 270kts on the GE's are a recommendation from the engine manufacturer and these are never hard numbers. In real life will it restart at 265 kts CAS on a cold day with high QNH??? Probably yes, you need sufficcient airflow and N2 RPM to get the show going. Does GE guarantee it below 270KCAS? No. The box is programmed to not start if you are below the recommended speed, but again this is a simulator! And there seems to be a bit of confusion here regarding APU/Autostart. Autostart is a function of the EEC, has NOTHING to do with the APU. In the Dual Eng Fail/Stall NNC the APU is started as a backup (remember it starts without you touching anything if both XFER busses are unpowered...) in case the engines do not relight at least you are getting AC and Bleed Air (below 22,000) from it, so the HEAT PITOT L+C+R will disappear in due time and at least you are not manually controlling the aircraft. The APU is there for AC not for APU assisted start.

- Why does the checklist omit the possibility to use the starter? (maybe because the subsequent ENG FAIL L/R does?...:sad:)

Again, I haven't seen this for a while, but my understanding is, that Boeing has developed this NNC with the possibilities in mind. If you go through 3000 AGL and both engines quit? Well, look for the softest spot... You don't have time for anything. At 10,000 with high terrain under... Well, again, you would need to be very unlucky. Now if they fail at FL370, you have substantial amount of time for a relight with windmill. If they do not start and you find yourself below 22,000 with APU running, yes, by all means do it from memory, -OR- use the In-Flight Start NNC as the ENG FAIL L,R will not be available, since you've cycled the Fuel Control switches from RUN-CUTOFF-RUN during the Memo items. This action will remove the ENG FAIL L,R.
What I think...

[potteroomore]

STBYRUD...your instructor must be one of those wonderboys who have never physically flown a B777 and make up porkies as he goes along! Could be those b767/757 boywonders who became alteon B777 instructors in kimchiland!:ugh: