Status Indication

[RodBearden]

I've just been watching a Mode S equipped Pilatus Turbo Porter paradropping, probably over Cark airfield in Cumbria. It was climbing quite rapidy, levelled for about 30 seconds, and then took about a minute to plummet from 13800ft to 1000ft (when it timed out).

In all that time, the status indicator said "Leveled". Does the aircraft broadcast this status as part of the Mode S transmission? If so, is it likely that this aircraft's transmission doesn't include the status, so RB just defaults to Leveled, or is there a fault with the transmitter?

Rod

[DaveReid]

In all that time, the status indicator said "Leveled". Does the aircraft broadcast this status as part of the Mode S transmission? If so, is it likely that this aircraft's transmission doesn't include the status, so RB just defaults to Leveled, or is there a fault with the transmitter?

That's a simple question with a complicated answer  :-)

Explicit climbing/descending/level data (i.e. Vertical Rate) can be sent in two different ways:

ADS-B-equipped aircraft send it as part of the Airborne Velocity Squitter (the same transmission that the groundspeed is calculated from).

Non-ADS-B aircraft, if they send Vertical Rate at all, transmit it as an EHS DAP (Enhanced Surveillance Downlink Aircraft Parameter) which RadarBox can't decode.

The UK Turbo Porters don't have ADS-B and the type is exempt from the requirements for EHS, so the only way that's left to detect if one is climbing, descending or level would be to compare successive altitude reports.  I don't know how RadarBox handles this.

HTH
Dave

[RodBearden]

Thanks, Dave - I thought you might pick this one up ;-)

I've just been watching it again and, as you suggested, it's not broadcasting VRate. RB is obviously not deducing the status from the altitude trend (over 10,000 ft per minute is quite a trend!), so it looks like it's defaulting to "leveled" in the absence of explicit data.

Rod