Can you correct a 12 degree compass error on a D-100

[pierre smith]

....without starting all over with a compass rose? I have read the manual and found the adjust feature but I wonder if 12 degrees is past the allowable error.

Thanks,

[jjconstant]

Hi Pierre
I just had my DAR inspection yesterday and it turns out I forgot the dang compass correction card. In the ensuing discussion, the DAR pointed out that many compass roses on airports sit directly above parallel magnetized rebar in the pavement or concrete.

He said the FAA is trying to figure out the answer, short of spending millions on "certified" compass roses!

He mentioned a plus or minus 10 degree level of accuracy, while mentioning the problem with the normal method of swinging the compass!

I get changes depending on what lights are on or off. He said technically the engine needed to be running (but warned of not doing this procedure with a non-broken in engine) and the avionics needed to be on, but no mention of lights or not.

All that being said if the Dynon is your actual source for heading stuff, I don't think I'd be comfortable with as much as 10 degrees of error...

all FWIW...

Jeremy Constant

[pierre smith]

...Jeremy. I decided to fly 24 miles to a compass rose that had been placed there by surveyors...very accurate. I stayed in the airplane with it running and did the 4 cardinal points entry and Voila...extremely accurate, because with the radios and GPS's all on, all the magnetic fields are in play.

Last week I noticed the big discrepancy between my 496 while taxiing and the D-100 was around 15 deg difference. Since the 496 and D-100 communicate, the 100 is able to calculate winds aloft since it has all the information it needs to do so..magnetic heading from itself and track info from the 496. It has airspeed info and the 496 gives it groundspeed...all it needs, except there was a 15 degree difference between the two units even in calm air, because of the error in the 100. This made the 100 think, "Whoa, a 15 degree correction...must be a heckuva crosswind up here!!"...and the winds aloft report was something to see....50 knot winds at 5500 feet...but it did what it could with the info it had.

Now it's really accurate since the heading is spot on.

The best,

[jjconstant]

So, did the dynon change for some reason that then needed the new correction? I understand the wind calculation -- the GRT does the same.

By the way, does the 496 show track in magnetic or true?

Glad it's all working now!

Jeremy

[carguy614]

Pierre..

Glad to hear you have the compass aligned. I found the calibration a bit tricky. Got your mag variance and intensity set?? if not, it makes a difference. I think you have to reswing the darn thing if you change the setting. Mine was off because I had the canopy open during the swing. My compass module is behind the baggage bulkhead, and the aft section of canopy rail interfered with it when the canopy was open. Watch where you stash that extra headset if your compass module is back there!! I used a compass and chalkline to aim mine, and I have it pretty close. As for the internal heading correction, it seems that if you correct in the NS axis, it skews the EW axis by half the amount, and vice versa. It remembers your setting, and this can confuse you if you don't zero it before flight. It was well worth the effort to recalibrate IMHO. As for winds aloft, data processed whilst in a turn will skew the winds aloft calculation quite a bit, and it takes a few miles on course to get an accurate depiction. I am sure you have figured this out by now, but thought I Would chime in anyway.

Thinking seriously about a 10.....
Chris

[pierre smith]

...from Dynon's web site and entered it into the 100.

I used the zip code of the airport where the compass rose is that I used....we're good to go

Best,