Altitude agreement

[RotaryLancair]

The altitude shown on my D-10A does not agree with my backup altimeter. How can i tell which one is correct? If i am in a closed hangar, and the engine not running, should my manifold pressure agree with one of them?? Assuming, of course, that two of the three are correct!!

RotaryLancair

 

[dynonsupport]

Unless they are way off, the MAP is not accurate enough to check them, and it doesn't work the way you might expect, the MAP is not your baro setting.

The traditional way to do this is to set both to your field elevation, and then check the two baro settings against ATIS / AWOS. If you have no local ATIS or AWOS, you probably do need to use a friend's altimeter as a tiebreaker.

The EFIS is adjustable +/- 600 ft so make sure nobody has messed with that.

 

[RotaryLancair]

i will check that today. i suspect the altimeter, not the D-10A. thanks for the quick reply!

 

[RotaryLancair]

i will have to admit, i was surprised! The ATIS gave an altimeter setting of 30.0. The altimeter was dead on! The Dynon was off by 350 feet. Oh, and my manifold pressure was reading 30.1.

i will now have to look at the instructions to see how to adjust the D-10A.
RotaryLancair

 

[RotaryLancair]

i assume this is the correct instructions for adjusting the altimeter
"ALTIMETER CHECK
The following test can be performed on an as-needed basis. If the altimeter is found to be out of specification, the following single-point adjustment can be performed by navigating the menus to SETUP > ALTADJ. In the Altimeter Adjustment menu, you can change the displayed altitude by up to 500 feet up or down. After making this adjustment, ensure that the altimeter on the EFIS-D10A meets the tolerances allowed between 0 and 30,000 feet. If this adjustment does not bring the altimeter on the EFIS-D10A to within specification at all attitudes, please contact Dynon Avionics to return for service."

i am not certain how to ensure the altimeter meets tolerances between 0 and 30000 feet.

RotaryLancair

 

[skysailor]

Testing the altimeter to 30,000 feet is a normal part of an static certification check in the US and required every 24 months for any aircraft to operate IFR. A shop who does this blocks off one static port while attaching the other to a calibration box. The box contains a Master Altimeter, hand powered vacuum pump, flow restriction and valves. Vacuum is drawn and metered to your static system while the reading on your altimeter (D10A in your case) is compared to the Master Altimeter. It must be within tolerance limits throughout the range. There is more error allowed at higher altitudes.

 

[RotaryLancair]

Support said, "The EFIS is adjustable +/- 600 ft so make sure nobody has messed with that."

i adjusted the altimeter yesterday, but i saw no way to tell if it had been previously changed. There were just +/- buttons to move the indication up or down. Should i have been able to tell?

 

[dynonsupport]

As you press the +- buttons, there is a window in the lower portion of the screen that shows you how much adjustment is being used. 0 or close to it is the default.

 

[RotaryLancair]

My D-10A seems to not be stable with the altitude. a few days ago, i adjusted the altitude up 140 feet to get it to jibe with the ASOS. today i had to adjust it down 220 feet to get the same result. i noticed after the adjustment and i had shut the plane down, i put power back on the dynon and the altitude was 60 feet high, then slowly over a couple of minutes came down to only 10 feet high.
how quick to react should it be and should in keep its correctness after an adjustment?

 

[dynonsupport]

After the unit has temperature-stabilized, say 10-15 minutes, it should be correct no matter how much you power it on and off, and it shouldn't change from day to day. Based on what you've described, we might want to have your unit back here for calibration.