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.