Anti ice and TRIM air switch query

[Driver170 42]

During the secure procedure i've seen a few pilots on videos and even pictures switching off the trim air switch and turning it on during the electrical power up procedure. So does this switch get turned off during the secure procedure?

 

Also why is this limitation observed - Turn off wing and engine anti-ice switches before entering the parking area.

 

[skelsey 765]

 

 

Also why is this limitation observed - Turn off wing and engine anti-ice switches before entering the parking area.

 

My guess would be to avoid the (pneumatically-operated?) valves becoming stuck in the open position once the engines are shut down -- I don't know the NG engine services well enough, but I suspect the air to operate the valves and, indeed, the anti-ice itself is tapped from the respective engine which could potentially then cause issues with the subsequent engine start.

[Driver170 42]

Good point simon! Anyone else...

[Copper. 78]

TAI - switched off for obvious reasons; Simon outlined the main reason.

 

Trim Air switch - TBC-18R2 Nuisance Zone Temp Light Illuminations on 737-800 Airplanes. Wheither you're supposed to turn it off depends if this bulletin applies to the aircraft.

 

To paraphrase someone --- Procedures that have no basis in reality are unnecessary, unsafe and annoying ---

[Driver170 42]

Thanks guys. Couldn't find anything about switching off the trim switch. Not on the NGX anyway lol

[kevinh 409]

My guess would be to avoid the (pneumatically-operated?) valves becoming stuck in the open position once the engines are shut down -- I don't know the NG engine services well enough, but I suspect the air to operate the valves and, indeed, the anti-ice itself is tapped from the respective engine which could potentially then cause issues with the subsequent engine start.

The engine A/I valves are pneumatic, but should close when pressure is lost as the engine shuts down. Wing valves are electric motor operated and would stay open. If anything the engine A/I valve opening during start would offload the compressor and might even help the start. But wing A/I bleed would reduce the air available for the start to an extent.

 

It's possible the reason thermal anti-ice should be switched off before entering the parking bay might be because if this was not done the wing leading edge and engine cowls would be being heated and so potentially dangerous to ground crew.

[scandinavian13 5,192]

 

 

To paraphrase someone --- Procedures that have no basis in reality are unnecessary, unsafe and annoying ---

 

I like that. So relevant in this industry, too.

[badderjet 181]

During the secure procedure i've seen a few pilots on videos and even pictures switching off the trim air switch and turning it on during the electrical power up procedure.

 

As it's not really mentioned in the secure procedure I see no point in doing this. Setting it to on during aircraft initialization makes sense as it is usually on all the time. I just don't see a reason to turn it off under normal conditions.

 

[Driver170 42]

As it's not really mentioned in the secure procedure I see no point in doing this. Setting it to on during aircraft initialization makes sense as it is usually on all the time. I just don't see a reason to turn it off under normal conditions.

 

Also the RW Airline SOPs that i have switch these off during the secure procedure!

[Copper. 78]

How old and what revision is the FCOM you are quoting? What do your pilot friends have to say? Does your FCOM have the FCOM-B's at the front?

 

Currently, there are no reasons to turn the Trim Air switch off unless the FCOM Bulletin (*TBC-18R2) applies, which shouldn't, because that problem got solved by a series of aircraft and part modifications. The only variable is whether the airline adopted these changes in their old 737s.

 

*TBC gets replaced by the 3 letter airline code, example RYR for Ryanair, so the FCOM Bulletin would be RYR-18 R2

 

Edit -

I think you're quoting from the RYR FCOM, and as such, the procedure must be done as laid out. Why they turn Trim Air OFF, I don't know. But I also find myself asking why their FCOM is as prescriptive as it is. I stand by my statement - there is absolutely no reason to turn the Trim Air switch OFF (as required by RYR -800 FCOM), unless FCOM Bulletin TBC-18 R2 applies to atleast one of their aircraft.

[Driver170 42]

Hi brian my FCOM and SOPs are dated 2014

Revision 24

[badderjet 181]

Also the RW Airline SOPs that i have switch these off during the secure procedure!

 

I stand by my statement - there is absolutely no reason to turn the Trim Air switch OFF

 

As said, second that...

 

[Driver170 42]

Well thats what the airlines SOPs i follow want you to do!

[Copper. 78]

As said, second that...

 

Thanks.

Well thats what the airlines SOPs i follow want you to do!

Well then, my guess is that there are still aircraft and/or parts in the RYR fleet or inventory that haven't been modified, and so the procedure to switch the Trim Air switch OFF/ON which was required by the aforementioned FCOM Bulletin, has been embedded in RYR's FCOM Normal Procedures, which might explain:

1) why TBC-18 R2 isn't in the Bulletin Record part of the RYR FCOM, and,

2) why it is a requirement as part of the RYR FCOM to turn the Trim Air switch OFF/ON pre and post flight.

 

All of this is misplaced information, as the NGX obviously doesn't suffer from the occurrence. This thread, and many others of yours, would have been better placed on another forum.

[Driver170 42]

Look i didn't know about the bulletin thing did i? Or i wouldn't of posted it, thats why i asked on here because it was odd