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>TRIM AIR OFF

Started by emerydc8, Mon, 25 Apr 2016 10:14

emerydc8

Hi Hardy,

I just happened to notice this issue. It's not a big deal, but maybe it's not hard to change either. When I turn the master trim air off on VG-BGY (B744ERF), I see the magenta target temperatures on the ECS synoptic next to the F/D, U/D and C/R. There are no magenta target temperatures next to the FWD or AFT main deck.

The FCOM says that with the >TRIM AIR OFF EICAS, the temperatures of the F/D, U/D, C/R and FWD and AFT Main Deck are all regulated by the F/D temp selector.

I can't remember if the target magenta is on all these zones during the backup mode or just the F/D, but in this case, it is on the F/D, U/D and C/R, but not on the FWD/AFT Main Deck. Is this correct? Thanks.

Jon D.

[ADDENDUM]: I see that Peter tried this already in a passenger sim and found that the magenta targets remained on all compartments and are all controlled by the passenger temp selector. On the freighter it is the F/D that controls in the backup mode. So, maybe there should be magenta temps in front of FWD and AFT Main Deck too? On the other hand, like you said, it could all be aircraft and/or company specific.

QuoteI tried option 1 on the BA sim last night. I can confirm that with the Trim Air switched OFF the target and actual temperatures remain for all compartments, and are controllable by the cockpit Passenger Temp selectors as normal, except of course that all cabin temps will display the same selected temp.

http://aerowinx.com/board/index.php?topic=3000.msg32230#msg32230


John H Watson

#1
QuoteThe FCOM says that with the >TRIM AIR OFF EICAS, the temperatures of the F/D, U/D, C/R and FWD and AFT Main Deck are all regulated by the F/D temp selector.

Strange....  The freighter maintenance manual (SQ) says that with TRIM AIR off, backup mode will keep the average temperature for all zones at 75F (24C). My Atlas training notes offer no clues.

QuoteI can't remember if the target magenta is on all these zones during the backup mode or just the F/D, but in this case, it is on the F/D, U/D and C/R, but not on the FWD/AFT Main Deck. Is this correct? Thanks.

I have a photo of the ECS synoptic on the pax aircraft with TRIM AIR OFF. All the magenta targets disappear except for the F/D. It's not explained in the manuals why this happens. I can't explain Peter's observations in the BA sim.

Rgds
JHW

(EDIT: I also reviewed the link to the previous message thread on this subject and was reminded of the options and limitations)

Avi

The return of a nightmare.
You open here a can of worms. During Alpha tests we had so many conflicting data about this system, Hardy simply had to choose something (and don't forget there are other switches and circuit breakers that affect this system in different models).

Cheers,
Avi Adin
LLBG

Hardy Heinlin

Hi Jon,

unfortunately, this part of the system is so airline specific and model specific, and undefined in the manuals; it's just beyond the scope of PSX's options repertoire.

So ... I'm sorry ... PSX can provide just one type of trim air system for all models ...


Regards,

|-|ardy

emerydc8

Thanks, Hardy. I realized that after I found the other post. No problem.

torrence

Just out of curiosity, what's the reason for so many company variants?  If I had to guess it's probably because Trim Air is not related to safety, performance, airworthiness etc.  So it falls into the same 'look and feel' and comfort  categories as livery, interior color schemes, crew uniforms, food choices etc. that are decided by the head office not the pilots and engineers (always assuming that whatever trim air option is used allows the crew to keep the flight deck comfortable enough to prevent sweat interfering with vision etc.).

Cheers
Torrence
Cheers
Torrence

John H Watson

I think there is just one option, Torrence... which perhaps was an afterthought. The engineers finally realised that there is no point disabling the whole temperature control system if there are still some computers in the system capable of producing a variable temperature (rather than a fixed average).

There are of course different pathways for trim air to the various zones on the different 744 types (Freighter, combi and pax configurations plus those aircraft with optional fore/aft lower lobe cargo airconditioning).

Trim air is always used unless there is a failure or cargo fire. Being able to turn off the Trim Air manually with the switch is a bonus (when the automatic protections fail).

torrence

Thanks for the background, John
So the complexity comes from all the permutations and combinations of the air system in difference models etc.
Cheers,
Torrence
Cheers
Torrence