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Random 777 questions, part 1

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Random 777 questions, part 1

Old 28th Jan 2023, 01:38
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Random 777 questions, part 1

Hi all, I hope I can tap into the knowledge base on this forum to answer a few 777 questions. Thanks in advance for the replies.

1. The door chapter says that at very high differential pressure, the vent flap cannot be opened. How high is very high?

2. Automatic WAI is inhibited when “Takeoff mode is selected” what exactly is takeoff mode? Does this refer to takeoff thrust (THR REF)?

3. Also, why’s WAI inhibited for the first 10 minutes?

4. Our manual states there’s no minimum oil quantity in flight, (but we do have a minimum for dispatch). How’s there no minimum in-flight oil quantity?

5. During a normal APU shutdown, can the shutdown be interrupted in the cooldown phase if you’ve changed your mind and decided to leave it running?

6. Does the APU fire bottle automatically discharge in the event of a fire in unattended mode?

7. In the flight control chapter, it says that in the secondary mode, simplified PFC laws lead to elevator and rudder being more sensitive at “some” speeds. Is this expanded upon anywhere?
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Old 28th Jan 2023, 07:48
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Hi, new on type myself but this is what I understand:

2. After pressing TOGA wing anti ice will be inhibited for 10 minutes

3. It probably has to do with the aircraft´s performance. If I can compare to the 737, though it does not inhibit wing anti-ice after TO, it does trip off automatically after setting TO thrust if previously selected on.
On a side note, in the FCOM it´s written that as soon as icing is detected engine anti-ice will come on. However for the wing anti-ice to come on, it needs to detect icing for multiple cycles. So it seems Boeing believe it is not that critical to have wing anti-ice on immediately after TO.

4. you don´t take action based solely on a low engine oil quantity. It should be combined with high oil temp or low oil pressure. For example, there is no low engine oil qty checklist on the 737.

6. FCOM 8.20.4 "on the ground with both engines off an APU fire signal from either APU fire detector loop causus APU shutdown and extinguisher bottle discharge"

If anyone with more experience and knowledge on the B777 has better answers, please correct me.
Cheers,-
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Old 28th Jan 2023, 08:42
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Originally Posted by Check Airman
4. Our manual states there’s no minimum oil quantity in flight, (but we do have a minimum for dispatch). How’s there no minimum in-flight oil
When the engine is running, the oil is in the engine, not at the place where it is measured. Pressures and temperatures indicate the oil functions as required. Valid for many jet engines...
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Old 29th Jan 2023, 07:21
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5. During a normal APU shutdown, can the shutdown be interrupted in the cooldown phase if you’ve changed your mind and decided to leave it running?
Absolutely, yes. Anytime you see the memo message "APU cooldown" it's fine to turn the APU switch back to run.
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Old 29th Jan 2023, 14:40
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Originally Posted by Check Airman
1. The door chapter says that at very high differential pressure, the vent flap cannot be opened. How high is very high?
[size=33px]
According AMM the vent door mechanism prevents door opening > .21 psid.[/size]
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Old 1st Feb 2023, 08:51
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Thanks all
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Old 8th Mar 2023, 05:46
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Originally Posted by Check Airman
2. Automatic WAI is inhibited when “Takeoff mode is selected” what exactly is takeoff mode? Does this refer to takeoff thrust (THR REF)?

3. Also, why’s WAI inhibited for the first 10 minutes?
Hi!
2. It looks likes “Takeoff mode” in this case is the same as for alert inhibits during takeoff: “Either engine in takeoff thrust range”.

3. Only automatic WAI operation is inhibited for 10 minutes. For manual operation it’s 5 minutes.
I agree with Rayfill, that’s done for performance reason, particularly for One Engine Inop takeoff. There’s extended 10 minute AFM time limitation for Takeoff thrust in the event of loss of thrust of one engine during takeoff. So they want to secure operating engine from inappropriate thrust reduction during that phase.
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Old 8th Mar 2023, 18:00
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The answers above are pretty good, I'll add a few things:
WAI draws a lot of bleed air from the engine - far more than ECS or Engine AI, so the potential impact to EGT margin is large. Further, on some Boeing types, WAI don't work if the slats are deployed as it opens the cavity that the WAI air is heating (not sure it that applies to the 777).
Oil quantity is 'advisory' only, and is not the most reliable or accurate measurement on the aircraft. An engine should never be shutdown in-flight for low oil quantity by itself - rather it's an indicator that you need to keep an eye on oil pressure and temperature. So long as they remain normal, no action is required.
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Old 8th Mar 2023, 19:54
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Further, on some Boeing types, WAI don't work if the slats are deployed as it opens the cavity that the WAI air is heating (not sure it that applies to the 777).
I think that applies to the 747, which has no slats, but instead has 'variable camber leading edge devices' that are flat sections which fold out from under the leading edge and are curved by an ingenious 'scissors' mechanism. The resulting void is indeed where the wing anti-ice hot air is directed and so it is not usable with the VCLEDs deployed.

On other Boeings with true slats, WAI is ok when they are deployed as the slats are not flat plates, but hollow, with enough internal space for a piccolo tube.
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Old 8th Mar 2023, 20:40
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Originally Posted by eckhard
On other Boeings with true slats, WAI is ok when they are deployed as the slats are not flat plates, but hollow, with enough internal space for a piccolo tube.
Memory also says it applies to the 737, but I wouldn't swear to that (WAI wasn't exactly my area of expertise).
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Old 8th Mar 2023, 21:50
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double

Last edited by Turbo Encabulator; 10th Mar 2023 at 08:36.
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Old 8th Mar 2023, 21:57
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Here's one. How come VNAV routinely starts down at TOD and suddenly decides that it's 2000 feet low on path and reverts to VNAV SPD? I"m like you're the one who calculated the TOD point
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Old 9th Mar 2023, 00:29
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Originally Posted by DNEMtin
Hi!
2. It looks likes “Takeoff mode” in this case is the same as for alert inhibits during takeoff: “Either engine in takeoff thrust range”.

3. Only automatic WAI operation is inhibited for 10 minutes. For manual operation it’s 5 minutes.
I agree with Rayfill, that’s done for performance reason, particularly for One Engine Inop takeoff. There’s extended 10 minute AFM time limitation for Takeoff thrust in the event of loss of thrust of one engine during takeoff. So they want to secure operating engine from inappropriate thrust reduction during that phase.
No.... Manual operation is not inhibited at all when airborne.
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Old 9th Mar 2023, 09:27
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I’d need to double-check this but if wing or engine anti-ice is turned on while the engine is at take-off thrust, I think the FADEC will maintain the thrust setting at the expense of EGT margins.
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Old 9th Mar 2023, 16:33
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Originally Posted by Fursty Ferret
I’d need to double-check this but if wing or engine anti-ice is turned on while the engine is at take-off thrust, I think the FADEC will maintain the thrust setting at the expense of EGT margins.
No, it won't. The FADEC receives the bleed status from the aircraft, and will automatically derate the max TO thrust to account for the bleed debits (in some cases it will also debit max climb, but I don't recall if that applies to the 777 or if it does, which engines).
The FMC will likewise derate the max TO rating to account for the engine bleed - so it's somewhat transparent to the crew unless you're using the charts to manually calculate the max TO limits. If Engine AI is selected for TO, the FMC will likewise decrease the max TO weight due to the EAI max thrust reduction.
The exception to this would be if the FADECs are in Alternate mode, they don't do the bleed debits, but the FMC still should.
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Old 10th Mar 2023, 09:22
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Yep, confused with previous type which would maintain T/O thrust at expense of engine margins until thrust reduction height. Thanks.

Have dug through the 777 manual and found the reference, thanks (current 787 pilot so while I'm apparently type-rated on the 777, the actual dynamics are obviously somewhat different, especially with bleeds).
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Old 10th Mar 2023, 10:35
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Originally Posted by Turbo Encabulator
Here's one. How come VNAV routinely starts down at TOD and suddenly decides that it's 2000 feet low on path and reverts to VNAV SPD? I"m like you're the one who calculated the TOD point
I know almost nothing about the 777 per se, but are you programming in all the descent winds?
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Old 11th Mar 2023, 06:28
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On the topic of engine anti-ice, the 777 seems pretty unique. It seems there are different performance packages. Some require only a minimal (200kg) correction for EAI on, while others require no correction at all.

That second set confuses me, as I’m not sure how the engineers managed that, but that’s what’s written in the performance section.
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Old 11th Mar 2023, 11:34
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Originally Posted by Uplinker
I know almost nothing about the 777
LOL. Don't let that stop you.

Yes BTW.
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Old 11th Mar 2023, 11:39
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I think RR engines adjust fuel flow to keep the EPR constant, whether or not engine TAI is selected, hence no perf correction?
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