Addition of extra Mode S data

[Dom2364]

If possible there is some data contained in Mode-S messages that would be nice to have in VRS
These being:

• Indicated Airspeed
• True Airspeed
• Magnetic Heading
• Mach
• Roll Angle

Indicated airspeed and magnetic heading I think are particularly useful, for example I have seen tankers while refuelling where ground speed is varying by 50kts due to wind, and indicated airspeed is being perfectly maintained. Magnetic heading is mainly useful if an aircraft is being vectored, and the autopilot heading displayed in VRS is magnetic which won't match the true heading.

[vradarserver]

Sorry for the delay in replying!

The ADSB spec lets aircraft transmit speeds as one of ground speed, IAS or TAS. VRS can (or should!) be able to tell what type of speed is being transmitted, it's the Speed Type value in the aircraft detail and aircraft list panels. It is not the case that all three types are transmitted and VRS chooses to only show one of them, it'll show whatever gets sent. However I've only ever seen ground speed getting transmitted. I think that's because the spec tells manufacturers to prefer ground speed if the aircraft is capable of calculating it, and if the aircraft is moving slower than something like 1000 knots.

Magnetic heading - the spec lets aircraft transmit either their true heading or the magnetic heading. Again VRS can tell which is being transmitted and will tell you via the Heading Type value. From memory the heading type is tied to the airspeed type, I think if it transmits ground speed then it also transmits the true heading over the ground? Not 100% sure on that. But for whatever reason I've only seen ground track getting transmitted.

It might be possible to work from true heading back to magnetic heading using the NOAA's magnetic model that they publish. That's been on the back burner for a while now, other stuff keeps coming up :) I'm still on their mailing list for that model, although come to think of it I've not had an email reminding me that I'm on the mailing list for a while.

There is a reservation in the airspeed type table for Mach number, but this is the same airspeed table where the spec tells manufacturers to send ground speed if they've got it so I doubt you will see many subsonic aircraft transmitting a Mach number if the spec ever makes good on it. As things stand though it's just a reservation, Mach numbers are not transmitted in ADSB V1 & V2.

Mach could be calculated if you know the temperature of the air at the altitude the aircraft is flying, but air temperature isn't transmitted so I can't figure that one out.

Roll angle isn't transmitted and I can't think of a way of calculating it given just the data that is transmitted. It would be nice to have the roll angle for use in flight simulators, at the moment I have a gnarly approximation in there. But no, I don't think I can do much about roll angle.