Removal of Wet Compass

[cliffy]

Mentioned in a current thread was the thought of removing the wet compass with a slaved HSI system

I seem to remember an FAA letter, directive, A/C or something that dealt directly with this issue signifying that it could be done under certain conditions

I can't find it 

Does anyone have that reference or know where it can be found? 

 

[MikeOH]

91.205(b)(3) Magnetic Direction Indicator

Doesn't a magnetically slaved HSI meet that requirement?

It does NOT say a magnetic compass is required.  What else would you need?

[Marauder]

Back when I went all electric with dual magnometers on two separate instruments, I asked about removing the compass. I can’t remember the explanation but it was due to the original type certificate or the minimum required equipment list that still requires it to be in the plane.

Be curious if there is an update to this requirement. I trust the accuracy of the mangometers over my mechanical compass.


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[N231BN]

The limitations section of the install manuals for any of the modern EFIS systems state that the fluid compass must be retained.

For an older slaved HSI, the remote compass would have to be certified to TSO C7 Type II.

A non-stabilized whiskey compass is a worthless instrument until you actually need it. If you are tired of a leaky compass an upgrade to a vertical-card is a good fix.

[PT20J]

The installation manual makes it required under the STC as @N231BN noted. Its also typically listed in the limitations section of the AFMS which makes it binding under FAR 91.9. Here’s an example for my G3X Touch…

[PT20J]

Of course, if you want to almost get rid of it you could mount it up high behind the copilot seat and view it with a mirror like Douglas did on the DC-9 

[EricJ]

On 1/15/2022 at 12:05 AM, cliffy said:

Mentioned in a current thread was the thought of removing the wet compass with a slaved HSI system

I seem to remember an FAA letter, directive, A/C or something that dealt directly with this issue signifying that it could be done under certain conditions

I can't find it 

Does anyone have that reference or know where it can be found? 

 

I don't know if this is what you were thinking of, but AC 23-1311-1c covers "Installation of Electronic Display in Part 23 Airplanes" and covers a lot of that stuff.   Sections 8.7 and 8.8 cover the required redundancy/backup and the magnetic heading requirements.   It specifically de-emphasizes the old compass definitions in favor of "magnetic direction indicator".

The Seminole I did my MEI training in was built in 2019 and only had 200 hours on it when I started my training.   It had a G1000 glass panel system and an Aspen as backup, and no magnetic compass.   It was apparently an issue when the school first got it and Piper provided a letter stating the certification basis for not having a compass, the details of which I don't have but might be addressed by the AC.

Edit:  Added pic of the panel from the Seminole with no compass.   Apparently whatever is here is sufficient to not need a traditional compass.

Edited January 16, 2022 by EricJ

[amillet]

52 minutes ago, PT20J said:

Of course, if you want to almost get rid of it you could mount it up high behind the copilot seat and view it with a mirror like Douglas did on the DC-9

Brenda is a retired school bus driver. Eyes in the back of her head. Would that count?

[LANCECASPER]

13 minutes ago, EricJ said:

I don't know if this is what you were thinking of, but AC 23-1311-1c covers "Installation of Electronic Display in Part 23 Airplanes" and covers a lot of that stuff.   Sections 8.7 and 8.8 cover the required redundancy/backup and the magnetic heading requirements.   It specifically de-emphasizes the old compass definitions in favor of "magnetic direction indicator".

The Seminole I did my MEI training in was built in 2019 and only had 200 hours on it when I started my training.   It had a G1000 glass panel system and an Aspen as backup, and no magnetic compass.   It was apparently an issue when the school first got it and Piper provided a letter stating the certification basis for not having a compass, the details of which I don't have but might be addressed by the AC.

Edit:  Added pic of the panel from the Seminole with no compass.   Apparently whatever is here is sufficient to not need a traditional compass.

The Aspen with its RSM has its own magnetometer, so I can see why that would get approved.  If the G1000 went dark I would sure rather fly the Aspen than the whiskey compass and the stars.

[Ragsf15e]

During my last F-15E flying deployment to Afghanistan, I actually used the whiskey compass for navigation twice.  Once was at night so the stars helped a little (you can see a lot of stars without any cultural lighting).  Neither time did I end up in Iran or Pakistan.  Damn “G1000” screen system reset once and the other time my INS crapped out.  It’s a useless instrument until you need it, then it’s priceless.

[PT20J]

1 minute ago, Ragsf15e said:

During my last F-15E flying deployment to Afghanistan, I actually used the whiskey compass for navigation twice.  Once was at night so the stars helped a little (you can see a lot of stars without any cultural lighting).  Neither time did I end up in Iran or Pakistan.  Damn “G1000” screen system reset once and the other time my INS crapped out.  It’s a useless instrument until you need it, then it’s a work of art.

I’ll bet you can really make it swing with acceleration and turns in an F-15! Where’s it mounted?

[EricJ]

41 minutes ago, Ragsf15e said:

During my last F-15E flying deployment to Afghanistan, I actually used the whiskey compass for navigation twice.  Once was at night so the stars helped a little (you can see a lot of stars without any cultural lighting).  Neither time did I end up in Iran or Pakistan.  Damn “G1000” screen system reset once and the other time my INS crapped out.  It’s a useless instrument until you need it, then it’s priceless.

The costs in acquisition/weight/maintenance are so small that I find it hard to justify flying without one given their reliability.

[Ragsf15e]

46 minutes ago, PT20J said:

I’ll bet you can really make it swing with acceleration and turns in an F-15! Where’s it mounted?

Yeah, also your leg timing gets tricky if you don’t set the throttles very carefully.  Apparently there’s a big difference between 350ktas and 500ktas.

[PT20J]

16 minutes ago, Ragsf15e said:

Yeah, also your leg timing gets tricky if you don’t set the throttles very carefully.  Apparently there’s a big difference between 350ktas and 500ktas.

Neat. Spruce sells an Airpath panel mount compass for $189.75. I wonder how much Boeing marks them up for the the Air Force?

[EricJ]

20 minutes ago, Ragsf15e said:

Yeah, also your leg timing gets tricky if you don’t set the throttles very carefully.  Apparently there’s a big difference between 350ktas and 500ktas.

Looks illegal to me.   I don't see a visible correction card anywhere. 

[N201MKTurbo]

I flew Eric’s plane to DMax before he bought it. The vacuum system quit 5 min into the flight. I flew it all the way to east Texas using the whiskey compass. It is easier with it than without it.

Most places you just get it pointed where you want to go with the compass, find something on the ground to aim for and fly to it. There isn’t much to aim for in Texas.

Edited January 17, 2022 by N201MKTurbo

[PT20J]

Years ago I flew from San Jose CA to Van Nuys and he KCS 55 gyro failed enroute. Next leg was to Chino. Visibility was 3 miles in smog. Flew to Chino with the compass. There are mountains about, but I never saw them. It was like flying in a brown tunnel. But the compass got me there. 

[RobertGary1]

In the md-80 they had trouble finding a spot to put the required compass that didn’t get interference so they put it behind the pilots. So that’s why the md-80 panel has a mirror l. 

[Ragsf15e]

13 minutes ago, RobertGary1 said:

In the md-80 they had trouble finding a spot to put the required compass that didn’t get interference so they put it behind the pilots. So that’s why the md-80 panel has a mirror l. 

The mirrors in the F-15E are to see if the WSO is still awake.

[cliffy]

On 1/16/2022 at 6:38 PM, Ragsf15e said:

Yeah, also your leg timing gets tricky if you don’t set the throttles very carefully.  Apparently there’s a big difference between 350ktas and 500ktas.

Looks like a standard rate turn at 0.9 M   to me :-)   WAAY TOO MANY BUTTONS ON THAT PANEL FOR ME :-)

Early Boeings (707, 720, 727 etc) had a fold away wet compass in the center bar of the windshield and we had a crew at Continental that went out for a check ride (in the days of check rides in the airplane) and the Fed wanted to see the compass pulled out and it wasn't there, someone stole it and no one checked before flight . Check ride failed. After that a fleet wide program commenced checking every wet compass and new procedures for checking the compass before flight were instituted. 

Edited January 18, 2022 by cliffy
spell

[cliffy]

On 1/16/2022 at 4:42 PM, EricJ said:

don't know if this is what you were thinking of, but AC 23-1311-1c covers "Installation of Electronic Display in Part 23 Airplanes" and covers a lot of that stuff.   Sections 8.7 and 8.8 cover the required redundancy/backup and the magnetic heading requirements.   It specifically de-emphasizes the old compass definitions in favor of "magnetic direction indicator".

Yes section 8.8.1 a &b is what I was trying to remember. Quite technical but in some instances the wet compass can go bye bye.  (Backup electronic heading indicator)

THX

[jaylw314]

31 minutes ago, cliffy said:

Looks like a standard rate turn at 0.9 M   to me :-)   WAAY TOO MANY BUTTONS ON THAT APNEL FOR ME :-)

Early Boeings (707, 720, 727 etc) had a fold away wet compass in the center bar of the windshield and we had a crew at Continental that went out for a check ride (in the days of check rides in the airplane) and the Fed wanted to see the compass pulled out and it wasn't there, someone stole it and no one checked before flight . Check rise failed. After that a fleet wide program commenced checking every wet compass and new procedures for checking the compass before flight were instituted. 

That's one of the more awesome stories I've heard from you guys 

[jaylw314]

On 1/16/2022 at 5:38 PM, Ragsf15e said:

Yeah, also your leg timing gets tricky if you don’t set the throttles very carefully.  Apparently there’s a big difference between 350ktas and 500ktas.

 

Oh, man, I know who I'm going to be pestering when the F-15E (some day) comes out for DCS! 

[cliffy]

1 minute ago, jaylw314 said:

That's one of the more awesome stories I've heard from you guys 

It was back in the late 60s that it happened when they still had the black and gold paint job.  

We called it  "The dirty bird with the brass ass"!