LOW VACUUM CAS MSG

[ChuckO]

Hi Goran - flying  the TBM9 v1.1.10 the other day I got a CAS LOW VACUUM message.  Emerg Procedure says to shut off/reset the bleed...but it didn't clear.  Postflight, couldn't find vacuum system in maintenance manager or in ECS diagram.  Curious to know what triggers the low vacuum message ?  Is there any way to clear this fault other than to start a new flight ?

Chuck O

[Goran_M]

Response from Saso (Who coded the TBM)

I tied that CAS message to the X-Plane vacuum pump system. But we never cause the system to fail, so something else must have caused it to fail. There's simply no code to write to the vacuum system fail dataref, so I know for sure it wasn't generated from our code.

 

I did a quick search through the code:

$ fgrep -Ir vacuum *
engine.c:    dr_t    vacuum_ratio;
engine.c:    fdr_find(&drs.vacuum_ratio, "sim/cockpit/misc/vacuum");
engine.c:    CAS_SELECT(dr_geti(&drs.vacuum_ratio) < VACUUM_MIN, CAS_VACUUM_LOW);
fail_mgr.c:    { "Engine", "Vacuum pump failure", XPFAIL("vacuum") }

The stuff in engine.c is simply the trigger for the CAS message - it looks at sim/cockpit/misc/vacuum and if it's low, it triggers the CAS message. The thing in fail_mgr.c is our custom failure control window (Flight > Edit Failures). That thing doesn't spontaneously generate failures, only on command by the user.

Edited December 20, 2019 by Goran_M

[ChuckO]

Thanks Goran -  It is a mystery  then.  The only thing I recall about that flight was that I let the engine run with the prop feathered in high idle for 10 minutes while waiting for my clearance.  It was long enough to trigger a text window hint to improve engine cooling by unfeathering.  The low vacuum CAS appeared during taxi out sometime shortly thereafter.  Perhaps doing that can somehow drop vacuum pressure and trigger the CAS ?  Cycling the bleed and shutting down the engine didn't clear it, but restarting X-Plane did.

Chuck

[Goran_M]

Perhaps check your X-Plane failures, too. Make sure they’re all set to always working. 

[ChuckO]

Good thought.  Found everything was working though.