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Loss of Trim Air

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Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
I would appreciate some technical imput from our engineering gurus regarding a Bleed Duct Leak from the centre duct in flight.

Bleed Duct Leak C - once the duct is isolated by QRH action then as you know the Trim Air is lost. In PSX the MASTER temps for the Passenger and Flight Deck are then either locked at present temp or set at an unchangeable 24C. I think that this should only happen however, in the event that there is a fault with the cabin temperature controllers themselves.

I think that what should happen with a loss of Trim Air is that the Cabin and Flight Deck temperature controllers can still be used within the quoted range of 18 to 29C in AUTO, although of course the individual zones cannot be controlled and will be blank (correct in PSX).

Also - can anyone confirm of you should get a ZONE TEMP EICAS for a loss of Trim Air due to the isolation valves being switched off for the leak, as QRH dictates?

Thanks for any input...

Peter
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
Pleeeze? Hardy would like some feedback on this as well..are you all away relaxing with a Pimms!?

Peter
Member
Registered: Oct 2014
Posts: 12
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
Hi Walter,

Many thanks - we have seen that but unfortunately there is room for ambiguity, that's why I think we need a maintenance manual to clarify exactly what all the little black boxes do!

Can you recall having anything like that ?

Glad to have you with us!

Peter
Member
Registered: Oct 2014
Posts: 12
Sorry Peter, I have no maintenance manual.

BTW, you do a good job here!!!!

Walter
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
Thank you! Sorry - I meant had you had it happen to you?
Feel free to join in!
Member
Registered: Oct 2014
Posts: 12
Hi Peter,

I never had this problem on a real flight - but of course it was included for training and checks in the simulator. Unfortunately I forgot a lot of details because I am retired since 1997.

Regards
Walter
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
Hello, Peter. I really would like to jump in on this discussion, but I am currently overwhelmed by setting up my layouts right now.

I do have the Boeing maintenance manual on Air Conditioning. It is a huge file but I can email it to you if you are interested. [Sorry I can't post the link to it here].

PDF Page 1205:
Quote
The EICAS advisory message >TRIM AIR OFF is displayed when the master trim air shutoff valve is commanded closed. The advisory message TEMP ZONE is displayed if a duct overheat has occurred or if the ZTC fails. The status message ZONE TEMP is displayed to indicate a failure of a zone temperature control system LRU. The fault may be isolated to the specific LRU with the central maintenance computer system.


Whether shutting off the L and R isolation valves and #2 pack (no air in the crossover duct) would be seen by the CMC as a failure of a zone temperature control system LRU I don't know. Our manual doesn't even show a ZONE TEMP EICAS -- just a TEMP ZONE. Maybe that's because it's just a status message.

Hope this helps.
Cheers,

Jon
« Last edit by emerydc8 on Thu, 02 Jul 2015 04:57:10 +0000. »
Member
Registered: Aug 2014
Posts: 24
« Last edit by kevmac86 on Thu, 02 Jul 2015 06:48:56 +0000. »
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
Kieber wrote
Hi Peter,
Unfortunately I forgot a lot of details because I am retired since 1997.

Regards
Walter

PSX will bring it all back to you Walter - it will be as though you never left!
Peter
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
@ Jon.
Thanks for the offer. The manual would be great. Perhaps you could try email or stick it in my Dropbox?

https://www.dropbox.com/sh/m7cxaety6mwtsqf/AAA4qg5PvBfEURh1vz5mmMyua?dl=0

Peter

@ Kev,

That's perfect. Many thanks!

Peter
« Last edit by Britjet on Thu, 02 Jul 2015 09:12:16 +0000. »
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
Hi Peter,

I'm not having any luck with the drop box. Your emal is hidden. If you want, please send me an email and I will send you the link.

a z e m b @ aol . com
Member
Registered: May 2010
Posts: 843
Quote
The trim air EICAS messages are shown on the main EICAS display:
- >TRIM AIR OFF: advisory message main EICAS display; trim air selected off (message inhibited when all packs are off)


Do you think you would get the >TRIM AIR OFF message with just the isolation valves closed?

I've been looking at the logic in the Schematics (21-26-05) and if the trim air valve "fails closed" and any pack is running, the trim air valve is commanded closed. According to my manuals, the TRIM AIR OFF message should appear if the valve is manually turned off or it is commanded by the PTC to close.

I can't find a definition for "fails closed" though. Might this be "manually commanded open and no pressure sensed downstream of the trim air valve"?

We would also need to know the definition of "any pack running" (Pack valve not closed?)

The pressure sensor is powered by DC Bus 4 via a CB on P180.

Rgds
JHW
Member
Registered: Aug 2014
Posts: 375
Location: Camberley, UK
John H Watson wrote
Do you think you would get the >TRIM AIR OFF message with just the isolation valves closed?


I think that if Pack 2 was still running - No..
Peter
Member
Registered: Aug 2014
Posts: 24
Any pack running is detected by "FCSOV open AND FCSOV Commanded open"

Also the pressre sensor down stream of the TAPRSOV, moitors the difference between the Cabin Pressure and the Valve outlet pressure, this is to detect Open/Closed failures.

Kev
Member
Registered: May 2010
Posts: 843
kevmac86 wrote
Any pack running is detected by "FCSOV open AND FCSOV Commanded open"


Where did you see this? I've seen some funny indications/messages in situations where the pack is not turned on and the pack valve is not fully closed (i.e. the logic sometimes isn't smart enough to figure out the pack is not actually running)

kevmac86 wrote
Also the pressure sensor down stream of the TAPRSOV, monitors the difference between the Cabin Pressure and the Valve outlet pressure, this is to detect Open/Closed failures.


I read this also, but why is cabin pressure involved?

Britjet wrote
I think that if Pack 2 was still running - No..


Understood, but I was thinking of the case mentioned before (engines providing air). Pack 2 would run only if the centre duct was pressured by APU or EXT AIR.

Rgds
JHW
Member
Registered: Aug 2014
Posts: 24
Hi John,

In a set of training notes that I have which are dated June 90, I have a schematic that shows the logic for pack operation and the PTC A/B.

Also it has the description for the operation of the pressure sensor. "A pressure sensor monitors the pressure differential between the cabin sense line and the downstream sense line. The transducer sends this information to the PTC for the CMC".

As for sensing the cabin pressure, the TAPRSOV supplies air at 10 psig above cabin. The pressure shown on the ECS Maintenance page is the diff pressure between the cabin and valve outlet as sensed by the pressure sensor.


Kev
Member
Registered: May 2010
Posts: 843
Kev, is there any logic in your books which says the TRIM AIR OFF message should not appear with the bleed duct isolation valves closed (all 3 pack switches on) with bleed supplied by the engines?

Packs 1 and 3 would still be running with the TRIM AIR valve closed. If you switched these two packs off, then I see the case for the TRIM AIR OFF message NOT appearing with no air on the centre duct because the pack running logic is not satisfied.
Member
Registered: Aug 2014
Posts: 24
« Last edit by kevmac86 on Mon, 06 Jul 2015 05:00:01 +0000. »

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