737 NG - Wing Anti Ice after Bleed Trip Off

[DCT_ELSIR]

In the ‘BLEED TRIP OFF’ checklist, Wing Anti-Ice is selected OFF. If TRIP RESET doesn’t work then it’s not available for the rest of the flight - “avoid icing conditions where wing anti-ice is needed”.

Bleed air for WAI on both wings should be available, since a pack has been switched off earlier in the checklist so the isolation valve will open in AUTO, meaning that bleed air is available for both wings.

Is there a reason why the checklist tells you not to use WAI if you can’t clear BLEED TRIP OFF? I assumed it was because one engine might not provide enough bleed air pressure for pressurisation, EAI and WAI, but this conflicts with the Engine Failure or Shutdown checklist. That checklist includes the step “Isolation Valve - Verify AUTO - this ensures bleed air is available to both wings if WAI is needed” which implies one bleed source can power all of the above.

What’s the difference between the single engine case and the Bleed Trip Off case? Is it that you will have descended in the single engine case and the issue is with bleed capacity at high altitude?

Thanks for any help.

[Vessbot]

It's triggered by excessive temperature and they don't want you to burn the wings off

[DCT_ELSIR]

Originally Posted by Vessbot

It's triggered by excessive temperature and they don't want you to burn the wings off

The bleed valve has automatically closed for the side with excessive temp though, you’re left with bleed from the other side which is normal. WAI should be available through the isolation valve which is open in AUTO as you’ve turned a pack off?

[skycruiser65]

Originally Posted by DCT_ELSIR

..... WAI should be available through the isolation valve which is open in AUTO as you’ve turned a pack off?

..which however should be handled with care, since one bleed source, powering both wings with bleed air and one Pack, which then switches to High is quite demanding, with the risk of Trip Off not only above FL350, as mentioned in the NNC. Problems could occur when in the descent with the ENGs in idle, so planning a "Power-On"-descent could be helpful.

[tdracer]

Wing AI is a very high bleed load - on the order of normal EAI and ECS combined. Trying to take all the bleed air from one engine is going to put a huge burden on the bleed system, and can easily result in its own issues.

[DCT_ELSIR]

Originally Posted by tdracer

Wing AI is a very high bleed load - on the order of normal EAI and ECS combined. Trying to take all the bleed air from one engine is going to put a huge burden on the bleed system, and can easily result in its own issues.

Thanks, that makes sense. So howcome the Engine Failure and Engine Severe Damage checklists allow you to use WAI through the isolation valve when single engine?

Is it because by definition you’ll have descended to at least drift down altitude when single engine thus reducing the pressure on the remaining bleed system?

[galaxy flyer]

Hint: BLEED TRIP OFF means you’ve had a bleed leak in the pneumatic system, you don’t want to create a high bleed load in a compromised system. In the OEI case, the bleed system is considered intact, so you can put a high load on it.

[Gin Jockey]

Originally Posted by galaxy flyer

BLEED TRIP OFF means you’ve had a bleed leak in the pneumatic system

Incorrect. BLEED TRIP OFF occurs because of a bleed air over temp ( > 490F) or bleed air over pressure (>220 PSI).

[galaxy flyer]

Oops, it’s an over temp or over pressure problem.

[skycruiser65]

Originally Posted by galaxy flyer

Oops, it’s an over temp or over pressure problem.

Affirm, see the the BLEED NNC (the -MAX-Version of the -NG - BLEED TRIP OFF NNC):

Originally Posted by galaxy flyer

Hint: BLEED TRIP OFF means you’ve had a bleed leak in the pneumatic system, you don’t want to create a high bleed load in a compromised system. In the OEI case, the bleed system is considered intact, so you can put a high load on it.

The leak is dealt with in the WING-BODY OVERHEAT NNC: