[ls8pilot]

Reading other threads about alleged vertical airspace infringements and transponder errors made me wonder....

If you have an ADSB device like SkyEcho what altitude is encoded and displayed to a ground station? The device itself seems to have both GPS Alt and a pressure altitude . I cant see any method of putting in a QNH to the device so assume that the pressure altitude return is based on 1013 hPa

So in a situation in the future where ATC are looking at ADSB transmissions, say in a Class G area underneath a section of Class D starting at (say) 2000ft, which altitude would be reported and if the pressure altitude would it be adjusted to the QNH for the day?

Presumably this will be relevant to the Barton trial ?

[rikur_]

1013

[Cub]

The Flight Level emitted from the Standalone ADS-B is adjusted in surveillance processor using the prevailing QNH to display altitude below the transition level.

[ls8pilot]

The Flight Level emitted from the Standalone ADS-B is adjusted in surveillance processor using the prevailing QNH to display altitude below the transition level.

Great - just what I wanted to know - thanks

[GolfHotel]

As a SkyEcho user for a couple of weeks. And very happy with it. I use it for ADSB in only.

These devises normally transmit the CABIN FLIGHT LEVEL. That is it uses the cabin pressure to work out its altitude. Cabin altitude can be quite a bit higher than the aircraft actually is at. Hope thats clear. I haven't phrased it very well.

ANY device transmitting its altitude should really be using the static source. IMHO

[Iceman]

It's the same for normal Mode-C/S transponders which use 1013 hPa as a reference in their altitude encoders. A lot of transponders will have a Pressure Altitude readout on their display and this is the value that is being transmitted by the unit. If you set 1013 on your altimeter then the transponder readout should correlate with the altimeter at all levels.

Iceman