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B-747-8 Mult Eng Fail/Stall and Engine X-BLD/XB Indications

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B-747-8 Mult Eng Fail/Stall and Engine X-BLD/XB Indications

Old 20th Aug 2023, 02:02
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B-747-8 Mult Eng Fail/Stall and Engine X-BLD/XB Indications

In the Boeing 747-8 Mult Eng Fail/Stall Checklist, first the memory items are accomplished which involve moving the affected engine fuel control switches to cutoff, then run.

Subsequently, the checklist asks the crew to deteremine whether:

Crossbleed indication X-BLD or XB is blank
-OR-
Crossbleed indication X-BLD or XB shows

My question then is: will the X-BLD or XB indication ever even appear while the fuel control switch is in RUN?

According to the systems manual, and the CAE cockpit procedures trainer (fixed base sim), it seems that it will not (in-flight start envelope altitude block and X-BLD indication is only present with an FCS in cutoff according to FCOM VOL 2, yet the fuel control switch will be in run when the Mult Eng Fail/Stall checklists requires the assesment of X-BLD's presence must be made).

Furthermore, if a crew does ascertain the need for an assisted start using the engine start switch, is there any automatic or time limited disengagement of the starter or closure of the start valve? The Mult Eng Fail/Stall checklist has as its last step:

"Do not interrupt the start attempts. Move the fuel control switch to CUTOFF only when no further start attempts are needed".

Is movement of the engine start switch(es) back to off when no further start attempts purposely omitted for systems reasons, or it just left to airmanship?

Thanks in advance!
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Old 20th Aug 2023, 02:18
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Originally Posted by RandomPerson8008
In the Boeing 747-8 Mult Eng Fail/Stall Checklist, first the memory items are accomplished which involve moving the affected engine fuel control switches to cutoff, then run.

Subsequently, the checklist asks the crew to deteremine whether:

Crossbleed indication X-BLD or XB is blank
-OR-
Crossbleed indication X-BLD or XB shows

My question then is: will the X-BLD or XB indication ever even appear while the fuel control switch is in RUN?

According to the systems manual, and the CAE cockpit procedures trainer (fixed base sim), it seems that it will not (in-flight start envelope altitude block and X-BLD indication is only present with an FCS in cutoff according to FCOM VOL 2, yet the fuel control switch will be in run when the Mult Eng Fail/Stall checklists requires the assesment of X-BLD's presence must be made).

Furthermore, if a crew does ascertain the need for an assisted start using the engine start switch, is there any automatic or time limited disengagement of the starter or closure of the start valve? The Mult Eng Fail/Stall checklist has as its last step:

"Do not interrupt the start attempts. Move the fuel control switch to CUTOFF only when no further start attempts are needed".

Is movement of the engine start switch(es) back to off when no further start attempts purposely omitted for systems reasons, or it just left to airmanship?

Thanks in advance!
Short answer is, the X-BLD start indication will display if the engine is not running, even if the fuel switch is in RUN (engine 'running' is based on logic in the FADEC). This is different on the 747-8 compared to the 747-400
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Old 20th Aug 2023, 02:28
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Originally Posted by tdracer
Short answer is, the X-BLD start indication will display if the engine is not running, even if the fuel switch is in RUN (engine 'running' is based on logic in the FADEC). This is different on the 747-8 compared to the 747-400
Great, thank you, I appreciate the quick answer. I think the procedures trainer is exhibiting inaccurate behavior in this case then. Good to know, as it has been the source of some confusion.
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