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  #1  
Old 08-22-2015, 05:00 PM
TXFlyGuy TXFlyGuy is offline
 
Join Date: May 2012
Location: Jazz Town, USA, TX
Posts: 505
Default Triple GPS

We will have a triple GPS installation. One will be IFR certified, the GTN-650. Does the FAA still require a wet compass? Why?
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  #2  
Old 08-22-2015, 05:29 PM
flyinga flyinga is offline
 
Join Date: Dec 2007
Location: Fredericksburg, TX
Posts: 667
Default

Wet compass is not required. Magnetic compass is.
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  #3  
Old 08-23-2015, 06:57 AM
mdevans9 mdevans9 is offline
 
Join Date: Jan 2006
Location: Hockessin,Delaware
Posts: 204
Default 91.205 (b)(3)

A "Magnetic direction indicator" is required. That does not mean a magnetic compass is the only way. The magnetic direction indicator on an EFIS meets the requirement. Of course, that EFIS must be operable to meet the requirement, as well.

Best regards,

Merrill
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Last edited by mdevans9 : 08-23-2015 at 06:58 AM. Reason: clarification
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  #4  
Old 08-23-2015, 07:11 AM
TXFlyGuy TXFlyGuy is offline
 
Join Date: May 2012
Location: Jazz Town, USA, TX
Posts: 505
Default

Quote:
Originally Posted by mdevans9 View Post
A "Magnetic direction indicator" is required. That does not mean a magnetic compass is the only way. The magnetic direction indicator on an EFIS meets the requirement. Of course, that EFIS must be operable to meet the requirement, as well.

Best regards,

Merrill
So...a G3X and a GTN-650 would fill the bill? Does the compass on an EFIS indicate mag heading, or mag track?

Last edited by TXFlyGuy : 08-23-2015 at 07:14 AM.
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  #5  
Old 08-23-2015, 07:17 AM
bcondrey bcondrey is offline
 
Join Date: Jan 2005
Location: Bellevue, NE
Posts: 528
Default

They all indicate mag heading, that's what the magnetometer does for you.
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  #6  
Old 08-23-2015, 08:31 AM
TXFlyGuy TXFlyGuy is offline
 
Join Date: May 2012
Location: Jazz Town, USA, TX
Posts: 505
Default

Quote:
Originally Posted by bcondrey View Post
They all indicate mag heading, that's what the magnetometer does for you.
So the GTN-650 / G3X Touch will satisfy the FAA requirement for mag heading without being supplemented by a separate mag compass?
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  #7  
Old 08-23-2015, 08:42 AM
jclark jclark is offline
 
Join Date: Jan 2005
Location: Columbia, SC
Posts: 804
Default

Quote:
Originally Posted by TXFlyGuy View Post
So the GTN-650 / G3X Touch will satisfy the FAA requirement for mag heading without being supplemented by a separate mag compass?
With the various EFIS products, Garmin or otherwise, it is the working **magnetometer**, providing info that you can see (via a display), that satisfies the "sensing" requirement.

So if you have a G-whatever and the magnetomer is not working, you have no "compass".

May sound like we are splitting hairs here but we are just trying to be clear. It is my understanding that the FAA wants you to have something in the plane that properly senses and shows to you your position in relation to the earth's magnetic field. They are not saying what the technology must be.

This is similar, I think, to the requirement for proper position sensor for ADS-B. If you have some technology other than WAAS GPS and can certify that it meets the specs, then go for it. Will probably take a few billion or so to come up with it though.
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  #8  
Old 08-23-2015, 02:20 PM
TXFlyGuy TXFlyGuy is offline
 
Join Date: May 2012
Location: Jazz Town, USA, TX
Posts: 505
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So as long as the magnetometer is functioning, and the EFIS display shows mag heading, we do not need a separate mag or wet compass?
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  #9  
Old 08-23-2015, 02:44 PM
flyinga flyinga is offline
 
Join Date: Dec 2007
Location: Fredericksburg, TX
Posts: 667
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No, you do not need a wet compass; as long as you have a "magnetic heading indicator" (electric, wet, laser ring or any other kind of magnetic heading indicator) you are good.
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  #10  
Old 08-23-2015, 04:10 PM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,283
Default

Make sure you run this by your DAR before he comes out. Not all of them are on-board with this interpretation, although I personally think it meets the rules. BTW, a laser ring gyro is a gyro, not a magnetic sensing device, unless it's hooked up to a flux gate or similar.
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