Mode S information
 

Hello all,

I'm interested to know how much can be seen by a controller from a mode S equipped airliner. I heard that callsign, selected level, selected speed could be seen however someone mentioned actual IAS is also visible.

In a unreliable airspeed situation this could be alarming/useful depending on the source data.

Thanks

There's no provision for selected speed AFAIK.

We can see Call Sign, Selected level, Indicated Airspeed/Mach number, Magnetic heading and selected barometric pressure. We also have feature of TCAS RA downlink.

Some info and examples of operational use at MUAC in this Eurocontrol video:

https://www.youtube.com/watch?v=9cQKPiGvD5Y

In London en-route airspace we can see:
SSR code, Mode C, selected FL, a/c hex address, actual IAS (so no speeding please!!), actual HDG, groundspeed.

Mode S information
 

It depends on the automation system being used by the controller. The information available in mode S downlink includes IAS, HEADING,CALLSIGN, FMS ID, AIRFRAME ADDRESS, ALTITUDE. Most modern systems show all these to the controllers. However to avoid clutter on the screens and to aid brevity the system administrators may choose to display only a few of these. Nevertheles access to view these is available albeit indirectly.