Setting for distance above sea-level incorrect for LHR

[apjwright]

Hi.  I'm still here at LHR and am having a problem with the 'distance above sea-level' setting.  For some reason, it is now thinking that LHR is 0ft - this is incorrect - it should be somewhere around 525ft.  When RB shows an aircraft as 0ft (ground), it's just barely at the threshold and still well up in the air ... any thoughts/suggestions?

Thanks,
Tony

[DaveReid]

Hi.  I'm still here at LHR and am having a problem with the 'distance above sea-For some reason, it is now thinking that LHR is 0ft - this is incorrect - it should be somewhere around 525ft.

Even the top of the new control tower is nowhere near 525ft AMSL - Heathrow's elevation is around 80ft.

[AirNav Support]

Hi Tony,

Are you connected to the internet when you are at Heathrow. If you are you can use smartview to get the latest metar (weather reports) from Heathrow. This will take the current pressure and adjust the alitude data sent from the aircraft to give you the correct reading.

Also aircraft which are on the ground may be sending out 0ft as part of there computer system just to indicate they are on the ground.

[apjwright]

Thanks for the responses.

I performed the SmartView metar weather report and it worked great.  FYI, aircraft are now showing as altitude 330ft when they touch-down.

Tony

[AirNav Development]

This feature was difficult to develop and something you will not find on any other flight tracking application. It is specially useful when the QNH is far from 1013 (now it is 1024).

[dudbaker]

Hi

I am having trouble with this.  I was of the belief that the crew set the QNH as they approach an airfield.  Then Mode C sends out what is displayed to the pilot.  I cannot see why Airnavs needs to know the pressure.  I am keen to learn.

[Allocator]

Dudbaker,

See the RadarBox Preferences setting - File > Preferences > RadarBox > Transition Altitude.

Below the figure set in the top box, altitudes will be displayed if the correct QNH (pressure at sea level) is entered.  So above the figure, Flight Levels related to the Standard Altimeter Setting 1013mb will be displayed.  Mode C always shows the level relative to 1013 mb.  RadarBox does the maths to show altitude.

If the airfield elevation is 500ft amsl, with the correct QNH set, the aircraft will show 500 ft as it touches down.

If you are connected to the Internet, you can set the QNH automatically using the Select Airport in the SmartView tab.

[DaveReid]

Hi

I am having trouble with this.  I was of the belief that the crew set the QNH as they approach an airfield.  Then Mode C sends out what is displayed to the pilot.  I cannot see why Airnavs needs to know the pressure.  I am keen to learn.

Mode S altitudes are always based on the standard pressure setting of 1013.2mb, regardless of where the aircraft is in relation to an airport.

Therefore in order to derive the true height, you need to adjust the transmitted height for the difference between 1013.2mb and the prevailing QNH.

HTH
Dave