J41CA
Member
- Joined
- Nov 25, 2001
- Posts
- 23
As mentioned the reason for the QRH procedure is to reduce the hot bleed air from thermal damage. 14th stage bleed air lines run through the pylons to the PRSOVs to the CMD valves out to the cowls and up the fuselage to the wing piccolo tubes. The bleed air leak can be anywhere and can cause significant damage. There is no guarantee that PRSOVs will close or leak. Therefore, the QRH procedure is to protect against that any significant amount of bleed air will get downstream to the duct failure point.
Depending on the EICAS message and aural you can pinpoint the area of the duct failure. If you recieve a L or R 14th Duct Fail EICAS message and a "Bleed Air Duct" aural, then the leak is between the PRSOV and either the wing or cowl CMD valve, which will be depicited red on the anti-ice synopic page. Plus, the associated L or R 14th SOV PBA on the Bleed Air Panel will have a red Duct Fail light.
If the aural is "Anti-Ice Duct", then the leak can be isolated from any point inside the wing CMD valve up to the wing. The section of the Anti-Ice synoptic that is red will either be the pipe along the fuselage or the wing is the area that has the leak. the duct along the fuselage has a single loop fire wire and the wing has thermal sensors behind the piccolo tube. This situation would present a red duct fail light on the Anti-Ice panel.
Another possible condition is a wing overheat, which basically is determined by thermal sensors in front of the piccolo tube attached to the wing looking for high temp. conditions. Wing overheat conditions may or may not be caused by a bleed air leak.
I hope the helps.
Depending on the EICAS message and aural you can pinpoint the area of the duct failure. If you recieve a L or R 14th Duct Fail EICAS message and a "Bleed Air Duct" aural, then the leak is between the PRSOV and either the wing or cowl CMD valve, which will be depicited red on the anti-ice synopic page. Plus, the associated L or R 14th SOV PBA on the Bleed Air Panel will have a red Duct Fail light.
If the aural is "Anti-Ice Duct", then the leak can be isolated from any point inside the wing CMD valve up to the wing. The section of the Anti-Ice synoptic that is red will either be the pipe along the fuselage or the wing is the area that has the leak. the duct along the fuselage has a single loop fire wire and the wing has thermal sensors behind the piccolo tube. This situation would present a red duct fail light on the Anti-Ice panel.
Another possible condition is a wing overheat, which basically is determined by thermal sensors in front of the piccolo tube attached to the wing looking for high temp. conditions. Wing overheat conditions may or may not be caused by a bleed air leak.
I hope the helps.
