Wrong altitude indication

[boehmda]

Hi,

In our installation we have a D-10A and a traditional airspeed and altitude indicator.

During testing we recognized a big difference between the D-10A and the traditional altimeter (speed is accurate within 1 to 2 kts). The traditional altimeter was tested for its tolerance and measures the correct values. The static system is for both units the same (static port to Dynon then to altimeter and then to the other static port).

I did then the correction in the setup menu, but the maximum of -500 was not enough. Have a look to the following values (both instruments at 1019mbar and the D-10A with the correction offset of -500):

Altimeter D-10A
6800 7620
7000 7720
7500 8330
9500 10350
9700 10550

Do you have any suggestion what I can do to get the correct readout?

Daniel Böhm
HB-YMF, Lancair 360

 

[dynonsupport]

An altitude that far off can't be much else besides a broken unit or a plugged static system. The static doesn't sound broken since your airspeed is right.

Sounds like it will need to come back. Please call or email us for an RMA number.

Just to check- you are setting the baro pressure on the EFIS to the same as your mechanical altimeter, right? You do need to set the EFIS just like all other altimeters.

 

[boehmda]

Yes, the baro settings were both identical at 1019 mbar.

So, I have to send the unit back... :-[

 

[rhouse9044]

I have a somewhat different problem with my D-100. I can adjust it to agree with field elevation and my conventional altimeter, but as I climb higher it reads progressively higher than the other altimeter and what ATC reads as my altitude. The error is 100' at 10,000'. If I reset the D-100 to read that altitude, it then reads 100' low upon landing. Is there any way to adjust this type of error out? Both the Dynon and conventional altimeters are plumbed to the same static line.
                Bob House
                RV9A N462BD

 

[khorton]

I have a somewhat different problem with my D-100. I can adjust it to agree with field elevation and my conventional altimeter, but as I climb higher it reads progressively higher than the other altimeter and what ATC reads as my altitude. The error is 100' at 10,000'. If I reset the D-100 to read that altitude, it then reads 100' low upon landing. Is there any way to adjust this type of error out? Both the Dynon and conventional altimeters are plumbed to the same static line.

Where is the transponder getting its altitude info?  From the D-100, or from a separate altitude encoder?  If you are using a separate altitude encoder, confirm it is plumbed to the same static line as the altimeters.

 

[n223rv]

I too have altimeter problems. I'm thinking mine will also have to come back... My altimeter seems to vary quite a bit on start-up. What happens is I set the barometric pressure to the ATIS. Some days we are spot on, other days we are +/- 300 feet off..... So I go in and offset the altimeter until the field elevation matches the barometric pressure and fly. Each time I fly, it seems like I have to do this in the range of +/- 300 feet to get them to match.

My problem is I don't have a back up altimter nor any other encoder (In that plane)....... So ATC see's whatever the Dynon says.....

I've had this problem since day #1, but I don't want to take the Dynon out as then I won't be able to fly....

It does this whether or not the static line is connected to the back of the unit... (verified on the ground).
-Mike

 

[Werner_Schneider]

Daniel,

before you send your unit back ask Rolf to bring on Saturday his D10A to Grenchen and we swap and see if you have the same error. Just easier before you finally send it back.

Werner

 

[dynonsupport]

The error is 100' at 10,000'. If I reset the D-100 to read that altitude, it then reads 100' low upon landing. Is there any way to adjust this type of error out?

ATC can only read in 100' increments, so a 100' error on what ATC sees from where you are may only really be a 51 foot difference between the EFIS and encoder.

Also, altimeters are allowed an 80 foot error at 10,000'. This means if you have two altimeters in an airplane, they can legally be 160 feet off from one another at 10,000 feet. Encoders only need to be within 150 feet of the altimeter, so they can be even farther off. So the real question is what unit(s) are "correct" in your airplane. While it may be the EFIS, it may be your other altimeter and/or encoder that are off.

To answer your other question, there is no way to adjust for "scale error" in the EFIS. This is all done at the factory in our calibration chamber.

 

[dynonsupport]

What happens is I set the barometric pressure to the ATIS. Some days we are spot on, other days we are +/- 300 feet off.....

Mike,
How far away and how real-time is the ATIS you are using? The purpose of ATIS has as much to do with matching up all the planes in an area as it does with being dead-on accurate to field elevation, so you may be seeing exactly the same variance with any altimeter.

The altimeter in the EFIS does have some settling time as the unit warms up. This is why we don't show you the altimeter for about 30 seconds. In reality, depending on the temperature of the unit (and how fast the temp is changing), we can have some error beyond those 30 seconds. We expect this error to be pretty small after a few minutes. Are you adjusting and checking the baro right away every time, or a minute or so after the EFIS is on?

When you come back and land, is the altimeter the same as it was when you took off, or has it drifted?

Have you had your EFIS tested locally? When you got your pitot/static certified they should have told you if the EFIS was reading properly or not.

 

[n223rv]

How far away and how real-time is the ATIS you are using? The purpose of ATIS has as much to do with matching up all the planes in an area as it does with being dead-on accurate to field elevation, so you may be seeing exactly the same variance with any altimeter.

Actually I live on a private strip and I have a Davis Weather Station with real time barometric pressure. Didn't want to go to that level of detail in the original post.

Are you adjusting and checking the baro right away every time, or a minute or so after the EFIS is on?

I adjust the barometric pressure right away. Then after the taxi and run up, I compare the displayed altimeter to the field elevation. It should be very warmed up by then......

It seems to be consistant within flights, but not between days. If I adjust it to be correct before the flight, it is the same at the end of the flight. It may be temperature related, so I will start writing down data as to the OAT, alt adjust number, barometric pressure, and field elevation. Maybe that will help troubleshoot.

It is not like my unit is just off, it is off a different amount almost every day I fly. Some day's I am +180 feet, other days I am off -180 feet. If everyones was off as bad as mine, everyone would be screaming. I guarantee there is something wrong, but I have not had the chance to send it back. I have had the same issue whether or not the static system is connected. When it is way off I can go to the back of the panel and unscrew the static line and it does not change.

 

[khorton]

Actually I live on a private strip and I have a Davis Weather Station with real time barometric pressure.  Didn't want to go to that level of detail in the original post.

What exactly does your weather station give you?  Is it actual barometric pressure, or sea-level corrected barometric pressure?  Neither of these is the same as altimeter setting.  How are you converting the output from the weather station to get your altimeter setting?  Maybe this conversion (or lack of conversion) is the source of some of the observed error.

What is the elevation of your air strip?

 

[grease371]

My D10A is doing the same thing.  One day it might be 380 feet off, then 180 on another day.  It is off by 300 feet or more most days.  I have not been able to detect a pattern and the problem is still there after the unit has warmed up for 5 minutes.  This has been since the unit was ungraded from a D10.  Before that it was right on the money every day.  I've been putting up with it for over a year because I hate to remove it.  My steam altimeter reads correctly day after day.  The D10A is also reading 2 mph slower than my ASI.  Before being upgraded they matched exactly.  Also, the AOA scale isn't responding like the usuer manual says it should.  The scale never shows full green when in straight and level flight.  It goes to the last red bar before the plane actually stalls.  I have calibrated the AOA four seperate times, using every configuration recomended but the scale readings remain the same.  The Dynon and steam guages are connected to the same pitot and static ports.  Are any of these symptoms related.  Do I need to return my unit?

 

[dynonsupport]

The altitude alone problem is indicative of an altimeter sensor issue that we'll need to have the unit back to fix. Give us a call at 425-402-0433 when you have some time to send it in.

The rest of the problems you're having definitely aren't related to the altitude issue. a 2 mph difference is going to be hard to troubleshoot because it's so small relatively, but when your unit's back here it's one of the things that we recalibrate anyway.

The AOA might be solved by doing the calibration a little differently. Give us a call at 425-402-0553 to chat about that issue (note the different phone number than for the warranty issue).