Outflow valve 747-8 [Archive]

torghabe

28th Apr 2018, 06:38

main_dog

30th Apr 2018, 07:21

First thing the checklist has you do is (manually) drive the failed outflow valve door closed (with the DC motor, so takes a bit more time), but as far as I know it will not happen automatically. Perhaps the AC motor was working intermittently?

Intruder

1st May 2018, 00:22

Hi there! Situation was: just after takeoff EICAS message L OUTFL VALVE illuminated and at CMC page was AC MOTOR. Crew do not start appropriate check list yet, but left outfl valve slowly moved to full close position. Why? The brakes should hold faulty valve when AC motor inop. Right valve operates normally. Control logic? I do not find answer. Thanks in advance!
What did the CMC say about the AC motor? Did it fail to operate, or fail to stop when commanded? Was it a transient fault?

You probably don't have the answer to these questions. That's pretty much by design, to help prevent pilots from second-guessing the EICAS and QRH, and delaying action while searching for info in the CMC. Why were you reading the CMC before the QRH checklist was completed? If you were a 3rd pilot on board, isn't your duty to assist with the checklists?

If the AC motor failed, the DC motor may have taken over trying to drive the valve toward CLOSE, while you were troubleshooting and [not] doing the checklist.

torghabe

4th May 2018, 08:14

What did the CMC say about the AC motor? Did it fail to operate, or fail to stop when commanded? Was it a transient fault?

You probably don't have the answer to these questions. That's pretty much by design, to help prevent pilots from second-guessing the EICAS and QRH, and delaying action while searching for info in the CMC. Why were you reading the CMC before the QRH checklist was completed? If you were a 3rd pilot on board, isn't your duty to assist with the checklists?

If the AC motor failed, the DC motor may have taken over trying to drive the valve toward CLOSE, while you were troubleshooting and [not] doing the checklist.
Hi Intruder! At CMC page- only AC MOTOR FAIL, nothing more, I was not PF\PM on this flight, of course, assistance for crew with QRH is not my responsibility, but this is our third problem with outflow valve at same plane. And last- an inquiring mind does not sleep.https://www.pprune.org/images/infopop/icons/icon7.gif
What does it mean "DC motor may have taken over trying to drive the valve toward CLOSE"? Before Manual select sw push? I would like to read about it. In any way Thanks!

Intruder

4th May 2018, 15:17

I was not PF\PM on this flight, of course, assistance for crew with QRH is not my responsibility
If you were in the observer seat, and a crewmember with the airline, this statement is VERY disturbing!

ANYONE in the cockpit has a responsibility to assist the operating crew when asked! OTOH, if you were NOT asked to help with anything, then it was your responsibility to keep your hands off the CDU!

main_dog

5th May 2018, 08:39

Ironically, I had this exact same failure on the takeoff roll last night (Eicas advisory alert OUTFLOW VALVE L at about 100 KIAS), albeit on a 747-400.

We engaged the A/P, actioned the QRH checklist, switched off one pack and drove the failed left outflow valve closed manually (so using DC motor). As far as I am aware the CPC automatically modulates outflow valve position using the AC motor, while DC motor is only for manual control; for sure that valve was going nowhere until we ran it closed manually.

From a practical perspective we noticed that the normal SOP of first cleaning up the airplane and then actioning the QRH might not be feasible: in our case the left valve had failed almost fully open, and even with the right one closed and three packs running the cabin was climbing at well over 1000 fpm, the old ears were starting to hurt. We elected to clean up partially and then action the checklist.

CCA

6th May 2018, 02:13

Outflow valves begin to drive towards closed and slightly pressurise the cabin once above 65kts ground speed which is then usually followed by a EICAS should the valve fail.

Sounds like an intermittent fault as others have said which is enough to latch the EICAS & CMC. Swap the AC motor at least to find out if it's a AC motor fault or not.

If they poster is not a pilot I don't believe they should be participating in running checklists, so glad they did not get involved.

torghabe

8th May 2018, 06:43

A lot of problem with outflow valves in 747th fleet is realy VERY disturbing situation. I think you knew, for closing outflow valve manually by DC motor you need more time and should hold in close position min 30sec (FCOM 742) or hold in close position until close (FCOM 744). If you have L(R) OV failed in open position after TO not delay appropriate QRH procedure, especially after T\O from high elevation RW. When you cleaninig up airplane with high vertical speed (more than 2300ft\min) you'll receive high rate of cabin altitude change due to one OV failed open. In this case CPC can't maintain programming alt and cabin alt rate and respectively will fail (both A and B). What do you think will happen with operable OV? Fail too. You meet with realy VERY disturbing situation , real situation and on FFS simulated situation. I'm engineer B1 and my question related only practical technical side.

CCA

8th May 2018, 18:23

In over 15 years of flying both the classic and 400/-8 I've had less than a handful of outflow valves failures. I'll admit on the classic it was a no brainer as the hairy fisted wise ones would manage it with aplomb. I'll also admit on the glass ones it's a personal memory item as it's no fun delaying it.

Turning the pack off is because having an outflow valve closed on the ground with three packs running leaves the aircraft slightly pressurised, making opening doors problematic, you could easily have some 400lbs keeping the door shut.

main_dog

9th May 2018, 11:42

I'll admit on the classic it was a no brainer as the hairy fisted wise ones would manage it with aplomb.

I miss the “hairy-arm autothrottle”... ;-)

torghabe

10th May 2018, 07:48

.......leaves the aircraft slightly pressurised
Nice knowledge, CCA! Pressurised via aft cargo heat, you should switch on it.