Altimeters not matching sometimes since P3D 5.1

aua668

Hi,

A difficult one: Since P3D V5.1 (Q400 Pro, latest version) I have at some flights (around one out of 20 flights) the problem, that from the loading of the aircraft the primary altimeter shows around 300-400 ft less altitude than the secondary. The secondary altimeter always shows the correct altitude. Only the primary altimeter shows at some flights an altitude which is too low although I set the correct QNH.I am not 100% sure, if I haven't seen this glitch also already in V 5.0. In V4 it definitely did not occur.

This mismatch doesn't correct during the flight and stays always the same. Restarting the simulator with the same flight corrects the problem. And then some flights later the mismatch appears again. The bad thing for the developers: I can't reproduce it and I could not detect any pattern. And I also don't get an ALT DISAGREE message on the PFD. Only the shown altitude on the PFD is too low. In the INI file I have set sync between CP/FO altimeters (PFD_QNH_SYNC=1
) and I have done hundreds of flights before without that problem. I also don't use the failure simulation. I always start cold & dark.

I use ASP3D as the weather engine. And I use AviaWorx for the CDU on a Android tablet. I also use some LUA programs in FSUIPC to connect my GoFlight equipment via the XML interface. As I am flying online on VATSIM, I checked with the controller at several altitudes and flight levels, that the value of the secondary altimeter is always showing the correct value. I have not actively checked, if the values are wrong on CP and FO side. I will check this, when the failure occurs the next time. I will also try to read-out the sim values via FSUIPC offsets and the Q400 simulation variables via XML interface, when it occurs the next time. Maybe I can trace it down. Any idea to identify the root cause is appreciated.

Rgds
Reinhard

aua668

Hi,

Did just another test and this time the PFD altimeter on the left side was 400 ft ABOVE the correct value. The altimeter on the right side and the STBY altimeter showed the correct value.

Then I closed the sim and started with the same flight - and now everything is correct.

It's getting even stranger.

Rgds
Reinhard

kroswynd

Hello,
Thanks for the update, and will take a look into this. I have seen at least one other report of this nature so we'll have to see what we can figure out.

Are you able to recall the airport and weather so that we might be able to recall it in ASN?

Cheers

aua668

Hi,

The flight yesterday was done in LFSB (Justsim scenery):

LFSB 181930Z 19006KT CAVOK 07/05 Q1025 NOSIG

Bale-Mulhouse, France (LFSB) 47-36N 007-31E 271M
Nov 18, 2020 - 02:30 PM EST / 2020.11.18 1930 UTC
Wind: from the S (190 degrees) at 7 MPH (6 KT):0
Visibility: greater than 7 mile(s):0
Temperature: 44 F (7 C)
Dew Point: 41 F (5 C)
Relative Humidity: 87%
Pressure (altimeter): 30.27 in. Hg (1025 hPa)

Today I tested also in LFSB with the weather shown above.

I went through my notes I took during the flight yesterday and I have to correct: Also yesterday the altitude showed 400 ft too high n the primary altimeter.

Rgds
Reinhard

kroswynd

Thanks for the update. I would also like to pick your brain for a minute.

1. During the SIM session in question did you observe any visual icing on the aircraft?
2. The next time that the issue occurs where icing can be seen or may be possible based on the temps (even if it isn't) turn the ISOL valve on the ice protection panel to observe if it will stop one of the altimeters from updating.

Thanks

aua668

Hi,

Icing was not the problem as far as I remember. I will check the next time the ISOL valve as proposed and report back. Thanks for taking care. If you are talking about the ISOL valve do you mean the "Airframe Deice Air Isolation Valve"?

Rgds
Reinhard

kroswynd

Yes Sir. Give that a shot, at the moment we suspect that it could be driven by a possible icing issue, but we could be off in that theory as well, but at least let's start here.

Cheers

aua668

Hi,

Yesterday I did a flight from EVRA to EFHK. The METAR was as follows:

EVRA 071520Z 14014KT CAVOK M01/M09 Q1022 R18/190095 NOSIG EVRA 071400Z 0715/0815 14015KT CAVOK TEMPO 0715/0716 15017G30KT TEMPO 0716/0722 15017G28KT

And again the primary altimeter on ground showed NEG 220 while the secondary altimeter showed the correct altitude of 37 ft for EVRA.

I tried your suggestion but without success. The ISOL valve did not change anything. The difference stayed during the whole flight. One interesting thing: When I turn the knobs of the primary altimeter, normally the scale moves accordingly. But when the difference exists, it doesn't move at all. It's frozen. After take off it starts moving (but of course with the initial difference).

Today I loaded the plane again at EVRA and everything was fine as expected. Same altitude on both altimeters.

Rgds
Reinhard

aua668

Hi,

After a long period without any problem, I experienced th altitude differenc again. departing from LOWI to LGKR the primary altimeter showed a height, which was 200 ft too low. The secondary altimeter was correct. Changing the QNH on the primary altimeter didn't move the altitude scale. It looks like if the altimeterdoesn't initialize correctly to the current QNH. Icing was no issue, as it was quite warm in LOWI. I am on 5.2 HF1 in the meanwhile.

Rgds
Reinhard

kroswynd

Hello,

Thanks for the report. if feasible if and when this is encountered again, could you immediately pause the SIM and then SAVE the SCENARIO, and zip it. Forward it to our Support email attaching this post to the email, please.

Cheers

aua668

Hi,

Wilco.

As this always happens immediately at the start, it's easy to check. I will save the scenario in such a case and I will send the ZIP to the support. There might be some time, until it happens again.

Rgds
Reinhard

kroswynd

Thanks

aua668

Hi,

I did now many flights, where this phenomenon was not arising. But today I could reproduce it twice in LIPZ. I did a first flight from LIPZ to LOWW and from the beginning the scale of the PFD altimeter didn't react, if I turned the knob. When I arrived in LOWW, I closed the simulator (P3D 5.2 latest HF) and started again in LIPZ. And it stayed the same. The altimeter scale was not moving, if I selected different QNH values. The values in the display changed accordingly. It looks like the altimeter scale always stays at standard QNH. The secondary altimeter was showing the correct altitude.

I saved the scenario as proposed, I also attached a screenshot from the PFD and also a screenshot from ASP3D with the current weather situation. I attach all files as a ZIP file.

I loaded then a flight in LOWW - same error. The primary altimeter scale was not moving, if I turn the knob.

Then I loaded the flight twice again in LIPZ an the altimeter worked. No idea, why it worked now and no pattern for constantly repeating it. That*s a really difficult one...

Rgds
Reinhard

aua668

Hi,

I think, I have found a pattern. I run on a second PC during my flights several utility programs like vPilot, ASP3D, etc.

If this phenomenon did occur, I always had ASP3D already running on the second PC, when I start the simulator with the Q400 situation. In that case this altimeter mismatch did happen from time to time.

I now always shutdown ASP3D, start the sim and after the Q400 is fully loaded I start ASP3D. In that combination it did not happen so far. I will continue to follow this procedure and hopefully this avoids this problem.

It might be, that ASP3D injects the actual weather at an point (sim ready), where the Q400 is just initializing and therefore is not able to handle this correctly.

So hopefully I have found a way to avoid it in future.

Rgds
Reinhard