D-180 Barometer off 100? Altitude

[Piper J3]

Just a general question? When I set barometric pressure to AWOS just before landing my altimeter shows 100? higher than field elevation when I touch down. Is this normal / acceptable? I sent the unit back to Dynon for airspeed malfunction last year and the repair order stated that the unit was completely checked for all functions and ready to return to service.

 

[Jesse]

I think there is an adjustment in the settings where you can change that. Only do the adjustment when the u it has sufficiently warmed up.

 

[rolivi]

How long after the AWOS did you land? 4 or 5 minutes and 100' might be curious, but here in Texas that wouldn't be a concern for a 45 minute old AWOS on a summer afternoon.

Try the "cheap-o test". Contact center, confirm the local baro, and compare what they see. On a quiet freq they'll help you out.

Otherwise, get that encoder checked.

 

[RFSchaller]

If you have a friend on the field try comparing your altimeter to his. If you have the D180/D100 dual EFIS you can compare them as they have independent barometric sensors.

 

[Handclutch]

Check the encoder settings. From memory the options are either 10' or 100'. I had a similar problem - altimeter always seemed to be 70' to 80' off even after it was calibrated and met requirements. I tightened the encoder setting and it's now very accurate, always within 10' - 20'.

Jack

 

[Piper J3]

Thanks Jack. I'll give it shot and report back.

Edit... Just got back from the airplane. D-180 was setup for 100' reporting. I changed to 10' reporting and unfortunately the altimeter still reads ~ 100' high when set to AWOS. I wondering if its a thermal problem. Seems spot-on when unit first powers up and then altimeter drifts about 100' when the the D-180 is running for a few minutes. This kinda makes sense now that I think about it. When I set altimeter to field elevation after engine start I often have to reset ~ 100' just before takeoff.

I emailed Dynon support to get their take on this. I'll report back when I get an answer...

 

[Dan B]

Try another airport or two before sending the D-180 off. Get the threshold elevation for the runway you are checking the altimeter at, not the airport elevation.

 

[Piper J3]

Try another airport or two before sending the D-180 off. Get the threshold elevation for the runway you are checking the altimeter at, not the airport elevation.

Can you advise how I get "threshold elevation for a runway"?

 

[Piper J3]

I just looked in the Dynon Forum and found a post similar to mine. Dynon says you can do a manual offset to correct altimeter for barometric pressure.

Dynon's response follows...

Not a calibration per se, but you can apply an offset. EFIS SETUP > ALTADJ - allows you to apply +/- 500 feet (assuming your UNITS is set to ALT: FEET) offset.

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So, back out to the plane today to apply this fix. I'll report in a few hours.

 

[Jesse]

I just looked in the Dynon Forum and found a post similar to mine. Dynon says you can do a manual offset to correct altimeter for barometric pressure.

Dynon's response follows...

Not a calibration per se, but you can apply an offset. EFIS SETUP > ALTADJ - allows you to apply +/- 500 feet (assuming your UNITS is set to ALT: FEET) offset.

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So, back out to the plane today to apply this fix. I'll report in a few hours.

Isn't that what I recommended?

 

[BillL]

Isn't that what I recommended?

You said "I think . . " and he went to looking to confirm your thought, so it sounds like you nailed it..


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