Barometer and altitude

[Guest Rajah]

Hi,Below the transition altitude PMDG and FS9 (Shft+Z)altitude are the same. Above there is a difference af about 500 ft. (at STD of 1013),How can I correct this?Frans Dekker TFF074A

[Guest Balrog]

Hello Frans!The reason for using a standard setting above transition altitude is that everyone is on the same setting, so that they don`t have to change the setting as the flight moves along. So it is natural that you see a difference such as this. The shift+z shows the aircraft true altitude above ground, but when you are flying the flight levels this does not matter. So you are not supposed to correct this, it is the way it should be.Cheers,Kjell.

[Guest Rajah]

Thanks Kjell.Your explanation is clear to me.I asked this because the ATC controller had a differnce of 500 ft on his radar and my actual altitude. Perhaps his problemAgain, thanks!Frans Dekker

[Guest Balrog]

Frans, that does not sound right. The altitude that ATC sees on their radars are from your transponder, it sends the altitude back to the radar displays.In real life.Now, I am on thin ice, because I have never flown with online ATC, and certainly not with the ATC provided in FS - I inly use real life flight plans, and the crappy ATC in FS don`t do SID and STAR among other things - better I control myself. One of the problems with ATC in FS is that it is American. No, not America bashing, but they use a set transition altitude of 18000 feet, which we don`t do in Europe. So now you know my area of operations....Question, was your altitude above 18000 feet, and was your altimeter calibrated to 1013HPa (or 29.91 inches)?Cheers,Kjell

[Guest Rajah]

Hello Kjell,I flew on line with IVAO in Holland and above the TA of FL040 with STD barometer=1023.That of the transponder I did not know. Interesting!So, the problem still exists.Thanks anyway!Frans Dekker

[Mats_J 2]

Hi Frans,> flew on line with IVAO in Holland and above the TA of FL040 with > STD barometer=1023This seems to have been your problem. Above TL FL040 you should set barometer to 1013 not 1023. This should not matter however if you pushed the BARO knob to get STD reading on the PFD.Hope it helps,

[Guest Rajah]

>Hi Frans,>>> flew on line with IVAO in Holland and above the TA of FL040>with >> STD barometer=1023 >>This seems to have been your problem. Above TL FL040 you>should set barometer to 1013 not 1023. This should not matter>however if you pushed the BARO knob to get STD reading on the>PFD.>>Hope it helps,>Unfortunately a type error: STD barometer=1013 !!!As you said STD=1013Frans

[Guest boxjockey99]

In real life the Transponder reports only the ALt set at 1013 regardless of the setting on the dial ie even if you set 999mb you will still be reporting an altitude calibrated to 1013, the baro setting knob adjusts the display not the actual reading. ATC can see the QNH altitude by pushing a button on their radar set which causes the correction to be applied to the reported altitude and then displayed on the screen! I have little experience with live ATC at present but I have had a similar issue, I look forward to reading any explanations others have!Kris

[Guest Rajah]

Kris,Thanks for sharing.You see: IVAO is as real as you can get!Frans DekkerB737-700 Flight Captain - IVAO :-)

[eurowing 13]

hi Frans,what was your standby altimeter setting? i have found that if there

[Guest Rajah]

Thanks Dennis,I am going to ceck this out,but first I am going on holidays!Let you know If I or someone of IVAO has a clue.Frans Dekker

[Guest Rajah]

As promised: I found an IVAO member with a very good explanation.With many thanks to Leo PrastFrans Dekker / TFF074ATo make it as simple as possible (well.... simple is not an option):shorthands used:APS = Altimeter Pressure Setting - I will assume currect APS setting by pilots and controllers unless stated otherwise.Metar = Meteorological Aeronautical Report (includes local pressure among others)AltitudesIndicated ALT = Indicated Altitude(s) (altimeter)Actual AMSL = Actual Altitude(s) above Mean Sea LevelActual AGL = Actual Altitude(s) above Ground levelFL = Flight Level = A-AMSL corrected for local QNHFLA = A-AMSL of flightlevelPressures1013 = Average airpressure at mean sea levelLBP = Local barometric pressureAAGL = Average Airpressure at Ground LevelQNH = Local airpressure corrected to mean sea level = 1013 - AAGL + LBPIn flightsim the METAR determines the reality as created by the simulator (both the pilot and controller sides). The pilot will adjust to this reality and fly accordingly.In Virtual flying all transmitted altitudes (to other pilots and to controllers) are Actuale AMSL. These are always correct by default because they are the basis for all calculations in flightsim. Pilot side:The pilot receives a metar with his version of the local QNH. FS will translate this metar to the reality for that pilot.The Indicated ALT for that pilot will be dependent on:- Actual AMSL flown (always correctly determined and transmitted to controller by FS)- QNH from metar (being pilot's reality)- Altimeter Pressure SettingController side:Actual AMSL is transmitted from pilot to controllerController software has his own metar (including his own local QNH)Below Transition level:- Actual AMSL as received is not changed and directly used as altitude in controller client softwareAt FLs:- Indicated FL is calculated using - Actual ALT as received from pilot side - QNH from metar (being controller's reality) Possible problems:As you can see there is a problem in the calculations: both the pilot and the controller use their own local simulation reality to calculate the indicated ALT. The QNH within that reality is the problem value being used in the calculations.Any difference in the reality-QNH between the two will make the controller see a different FL than the one the pilot is flying.Causes for these differences are many. Some would actually also exist in real life, some are caused by the limitations of our simulated virtual airspace and the choices we make in where we take our reality (metar or weather information) from.Where do problems pop up?Problems can pop up both above and below transition level1. Below transition levelThe pilot is ordered to descend through the Transition altitude with " Friendship 314, descend to 2000 feet, qnh 1021"He sets the APS manually to this 1021Problem: pilot's local reality has a QNH of 1013 (no real weather set)Pilot's APS is not equal to the QNH of HIS OWN realityPilot's indicated altitude will NOT be real altitudePilot is not aware and descends to indicated 2000Actual AMSL (approx 1500) is sent to controllerController client will not recalculate and therefore report actual AMSL 1500Solution: pilot should use HIS OWN reality QNH (use B in FS to set automatically)2. Above transition levelThe controller will give the pilot a command to go to FL220The pilot has APS 1013 set and climbs to FL220 INDICATED on his altimeterThe indication is based on his reality and the QNH in his metar.The pilot flies perfectly within his own simulated realityActual AMSL = 22.000 feet = sent to controllerProblem: controler reality QNH = 1021Controller client will recalculate actual AMSL to FL using QNH=1021Controller client will translate actual AMSL to FL 215Solutions: - preferred: do nothing - controller should be aware and adjust commands accordingly- not preferred but possible: - controller reports FL215 to pilot - pilot adjusts APS so that altimeter indicates FL215 - pilot climbs to FL220 - controller should expect same problem other way around laterI hope this long read helped in understanding the problems.Leo Prast / TFF314