Answered: Altitude, weather generator vs SimAware

[John Stockton]

Thanks for all the replies below. I guess I asked the wrong question. This time I'm looking for a Yes or No.

Is the altitude, of my plane, that I see on SimAware the same that ATC sees on their radar?

Please accept my apologies on the previous original question (erased). I think I got too fancy in my wording. The more I think about it, this should have been posted in General Discussion. Mod's please move if you agree.

Edited February 13, 2021 at 08:56 PM by John Stockton

[Koen Meier]

If you remain below the transition layer then you could update you qnh or inhg every half an hour or so. But once you go above the transition layer you should be on standard. Keep in mind that the altitude meters can be off by a 100ft between the pfd and standby gauges. I would stick with what atc tells you or what the metar tells you. Weather engines use metar as well except for msfs I believe.
 

on a side note a simulator like psx has a custom pressure system that is more accurate and therefore gives deviation to what ATC expects.

[Mike Sweeney]

hi John,
In case this helps ....
When abv transition altitude (in flight levels), set the aircraft's altimeter to standard pressure (29.92/ 1013); the aircraft will display on VS ATC radar clients at the correct level.
Each ATC radar client has a setting for transition altitude which may be manually set by the controller for their corresponding sector.
Example:

[John Stockton]

Completely aware of 18,000' and above= 29.92" in USA. Being GA I'm seldom at Transition altitude, typically VFR, 10,500' / 9,500'. A better question would be....

Does VATSIM ATC show the same altitude on their radar as I see on SimAware?

Edited February 13, 2021 at 05:53 PM by John Stockton

[Robert Shearman Jr]

Above transition, keep it on standard and don't mess with it.  Controllers are well aware that this means you may be a few hundred feet above or below what's showing on your altimeter, depending on the actual local pressure around you.  Everyone around you should be doing the same, and tampering with it potentially violates vertical separation. 

[Dustin Rider]

When you fly below transition altitude, always use the altimeter setting ATC gives you. If you're not talking to ATC, just find an ATIS or AWOS/ASOS (or their VATSIM equivalent: .metar [ICAO] in your pilot client) every hundred miles or so and readjust your altimeter to the local station.

I'm not sure to what extent the relationship between mode C altitudes and ATC computers (our radar clients) is modeled here on the network. In the real world, Mode C-equipped transponders send encoded pressure altitude data to the FAA, whose ATC computers take that and, for aircraft below FL180, correct for local altimeter settings. Since everyone uses 29.92 above FL180 (in the US, at least), pressure altitude is equal to aircraft altitude and no corrections are necessary.

I don't know what data gets passed between the network and software like SimAware, but I'm sure it isn't corrected for different altimeter settings, and if you're using that as your altitude reference, ATC will show you either too high or too low.

[Ross Carlson]

3 minutes ago, Dustin Rider said:

When you fly below transition altitude, always use the altimeter setting ATC gives you.

To add to this, be sure that the ambient pressure in your sim matches what ATC thinks it is. (Which should be the case if you are using a real-world weather source for your sim.) If for any reason the pressure in your sim doesn't match what ATC gives you, the value you enter into your altimeter should match what your sim thinks the pressure is, not what ATC gives you.

[John Stockton]

I changed Original Post. 

[Mike Sweeney]

Hope this may help, subject to correction by Ross and experts:

Below Transition altitude:
-Set aircraft's altimeter to local pressure  (as provided by online ATC and/or as should match local pressure injected into the simulator by a weather engine)
[On legacy simulators, hit the "B" key to set local pressure]
-Fly the assigned altitude (i.e. indicated altitude shown on altimeter should be flown, as assigned, or as appropriate for direction of flight for IFR/VFR flight rules)

On the ATC side, the VATSIM radar client will then show the correct altitude is being maintained.
Vertical separation is ensured.

Whereas altitudes displayed by 3rd party applications, simaware, servinfo, etc are largely irrelevant. (unless perhaps local pressure coincidentally matches std pressure ?)
What's important is the altitude displayed for the aircraft on ATC's radar client, and that data comes from the aircraft's altimeter (transponder), combined with accurate local pressure setting in aircraft's altimeter.

For example, rw, pilots do not fly gps altitudes shown on an EFB.
Pilots fly the assigned altitude with the correct local pressure setting in the altimeter (kollsman window for non-digital avionics).

TL;DR
Forget whatever altitude is shown on servinfo, simaware map, etc.
Set local pressure in aircraft's altimeter (update periodically when flying into/through areas with different local pressure), and fly the assigned altitude.
The ATC Radar client will calculate and display the correct altitude is being flown, on the local pressure setting.

Illustration:
If I see an aircraft (in VRC for example) cruising at 7,200 (with 7,000 assigned) and I prompt the pilot to re-set their altimeter to the local pressure setting, typically within seconds thereafter for an aircraft with altitude hold autopilot, the aircraft then appears level at 7,000 on the radar block in the ATC client.

Hope this helps.
Again, subject to correction if any inaccuracies (Ross)?

Edited February 14, 2021 at 05:00 PM by Mike Sweeney

[John Stockton]

1 hour ago, Mike Sweeney said:

Whereas altitudes displayed by 3rd party applications, simaware, servinfo, etc are largely irrelevant.

For example, rw, pilots do not fly gps altitudes shown on an EFB.
Pilots fly the assigned altitude with the correct local pressure setting in the altimeter (kollsman window for non-digital avionics).

Forget whatever altitude is shown on servinfo, simaware map, etc.

Perfect! Thank you.