DC HSI?

[201er]

I have a Kings KCS-55A HSI. It has a mark on the top that says DC and dedicated circuit breakers. What I am trying to find out for my instrument training is whether or not this isntrument is dependent on the vacuum system or is electronic and self contained? Anyone familiar with this?

[danb35]

The DC means that it's electric, not vacuum.  It's not completely self-contained, though--it's also connected to (and requires) a directional gyro in the tailcone, and a fluxgate mounted in the wing.  All of those, though, are electric, not vacuum.

[201er]

So in other words, the HSI would be completely unaffected by a vacuum failure but completely inop in an electrical failure?

[carusoam]

201er,

 

That is why the DC is directly on the instrument face.  To test your theory, or demonstrate to your flight instructor, you should be able to erect the gyro solely by electric power without the engine generating a vacuum.

 

My AH is marked AIR.

 

Of course this information should be readily available in your POH.  If you have an AP, it might be all collected in one place (ah, hsi, AP, slaving etc.)

 

Best regards,

 

-a-

[danb35]

Quote: 201er

So in other words, the HSI would be completely unaffected by a vacuum failure but completely inop in an electrical failure?

[carusoam]

Check to see if you AH also has an indicator for power failure.  As Dan pointed out, your battery will supply power for quite some time.

 

However, if you don't notice the generator failure until the lights flicker, it would be good to know when the AH no longer has usable electricity. Some mooneys have dual batteries.

 

Consider checking the health of your various generator failure warnings.

 

This is IFR critical since your backup is an electric powered turn coordinator.

 

Best regards,

 

-a-

[jetdriven]

His vacuum powered AI is still going in case of  DC power failure as is the wet compass.  The king setup is about the best available in those planes. 

[carusoam]

Somewhere in there I crossed AH with HSI. Sorry.....

 

Losing an HSI in IMC.... not so critical.....

[jetdriven]

Its pretty important on an ILS to minimums.  But overall not a killer failure.