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Compass Deviations "T" Model


HercRep
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OK guys, anyone run into this one before? Initially the desc. was for the sandby (wet) compass being off more than 5deg. It was replaced, the flt deck was checked for mag fields, and de-gaused. It then went to compass rose for verification, which it passed. On check flight, it was discovered that BOTH C-12's, AND the standby were reading off simultaneously, BUT only on certain headings, and the deviation was not the same from one to the other. INS's, GPS are rock solid. The desc. is intermittent, and deviations are not on the same headings each time, it always checks good on deck.

Now the odd part, several other type A/C on the field are experiencing compass variation, 5 A/C in all. We all operate in the S Atlantic/ Carribean area. What do you think? (and dont say its the Bermuda Triangle!)

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NOTE to all.... This "oil" response started as a joke...

MUST BE THE OIL IN THE GULF...

However after a short google search (yes I do own stock)(not really) I found this...

http://www.terrapub.co.jp/journals/EPS/pdf/2006/5810/58101401.pdf

So maybe I'm right!!

Or it might be the polar shift that is going to "change" the world in 2012.

Didn't "we" "change" the world in 2008?

What aircraft is that on your profile?

(and dont say its the Bermuda Triangle!) Have you eliminated it as the cause?

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I remember from flying Cessnas and Pipers in my earlier days that they would have compass cards. The compass will show different deviations on different headings because of the metal in the airplane and it's relative position to the compass needle. I imagine it'd be the same in the Herk, but don't recall seeing a compass card. I remember going out with a mechanic and filling out the compass card on the little Grumman I used to fly.

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Guys!!!.good morning to you!!!..........I think that the "World", as we know it is changing. Soon, we're gonna be Butt.F... . Sorry for my dirty language!!.......Cheers to you all!!......................John Boy the Tusker!!!

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OK guys, anyone run into this one before? Initially the desc. was for the sandby (wet) compass being off more than 5deg. It was replaced, the flt deck was checked for mag fields, and de-gaused. It then went to compass rose for verification, which it passed. On check flight, it was discovered that BOTH C-12's, AND the standby were reading off simultaneously, BUT only on certain headings, and the deviation was not the same from one to the other. INS's, GPS are rock solid. The desc. is intermittent, and deviations are not on the same headings each time, it always checks good on deck.

Now the odd part, several other type A/C on the field are experiencing compass variation, 5 A/C in all. We all operate in the S Atlantic/ Carribean area. What do you think? (and dont say its the Bermuda Triangle!)

Are the C12 Amps and Gyros compatible? Again, just more proof that installing a 2nd INU would have been a money saver. They could have done it during the autopilot mod.

Edited by tinyclark
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Sorry for the oil stuff, kinda funny though...

The Brass screws are a good start. but this should show up at compass cal.

Check and make sure the same test equipment is not used on all the affected aircraft.

Also there is (used to be?) a "wet compass" fly heading card that is filled out.

IE: fly 123 to track 120.

A compass heading deviation greater than ±2 degrees of the INS reference heading or a standby compass heading deviation is greater than ±5 degrees of the INS reference heading, the compass needs to be calibrated.

I would assume (but you know what they say about that) your deviations are greater than those limits.

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