What Did I Pickup 280nm Out?

[Falcon]

Hi,

I wasn't recording but my polar diagram which has been building for a couple of days picked something up from 280nm out in each direction travelling in a east - west or west - east direction. It obviously exceeds the mode s max range rings. Its an even 280.2nm in each direction. I always lose aircraft out to the west pretty much consistently in the same place as you can see.

Could some sort of glitch somewhere cause this.

Any ideas?

Thanks

[kdt1]

Hay Falcon

I have noticed at times some ADS-B equipped planes
send out faulty positional data. So one second there in Florida
and the next there in Africa or in your case 280+nm on either
side of you. That’s my thought anyways.

Cheers

[viking9]

It's a spurious signal of some sort. I get one running approx north/south every few days.

Tom

[AirNav Support]

Aircraft such as gulfstreams are sometimes quite common in doing this. Some people are suggesting its to mask there positions.

[viking9]

Aircraft such as gulfstreams are sometimes quite common in doing this. Some people are suggesting its to mask there positions.

Not so. It only happens on AirNav. When it happens I check on PP and find that I can track the aircraft perfectly, SBS users have told me that they have not seen this problem.

[DaveReid]

I agree - I think that suggesting aircraft are transmitting incorrect coordinates to conceal their position is disingenuous.

There are/were a very small number of aircraft with bugs resulting in incorrect coordinates being generated via ADS-B.  One was B733 EC-JTV, which was flying for Hola until a few months ago. Another, also a B733, was OM-HLB and ditto B735 LZ-BOY.

I've never picked up a Gulfstream transmitting obviously incorrect coordinates, although I recall in the early days of SBS a bug in the Kinetic decoding algorithm produced spurious coordinates for some Challenger aircraft.

Not that I'm suggesting that RadarBox has a similar bug affecting Gulfstreams, of course.

[AirNav Support]

Its hard for us to confirm this either way unless someone wants to lease us there Gulfstream for a nice test run?

[Keith L]

I just had a Grob Tutor indicating 40000' for a short while before reverting to a more believable 4570'.  Just noticed another Grob Tutor at 12,000 which is unlikely given that it isn't pressurised.

[Fenris]

Its hard for us to confirm this either way unless someone wants to lease us there Gulfstream for a nice test run?

Surely someone who sees the problem frequently could be provided with a version that captures internal RB processing data so you could see what is happening?

[AirNav Support]

At the moment we don't believe this to be a RB fault as the position data fault would mean all aircraft are affected as they send the same type and format of data (ADS-B) which is not the case.

We do believe this effect is down to specific aircraft spoofing there position deliberately or a faulty transponder.

[DaveReid]

At the moment we don't believe this to be a RB fault as the position data fault would mean all aircraft are affected as they send the same type and format of data (ADS-B) which is not the case.

We do believe this effect is down to specific aircraft spoofing there position deliberately or a faulty transponder.

That's what Kinetic told users in relation to the Challenger position bug.  Coincidentally, the bug disappeared when they brought out an SBS firmware upgrade.

Either that or they sent a team around the world fixing faulty aircraft transponders ...

[AirNav Support]

There are still reports from SBS users with aircraft jumping and changing heading etc.. but we won't discuss what bugs or issues they have.

Some of these position movements only happen over land or at certain times. This would not present a bug in decoding as it would mean it should affect all aircraft virtually all the time. If you think you know why, then were happy for you to contact us and show us the light? :)

[jgrloit]

For the cockpit aware amongst the users -
Do Gulfstreams have more than 1 transponder?
If so then it sems as though one of them may be picking up, and forwarding incorrect data - possibly 1 using radio altimeter and the other an airtube based one - possibly giving different heights.
Could the positional be from GPS for one and inertial guidance system for the other, or is the second one giving ground accuracy, by mistake and fooling the systems.   ground positions being repeated every 98Nm?
The transponder theory being prompted by a comment on an Airframe comment on a particular aircraft giving different ModeS Id-s on different transponders on The Commercial aircraft in the Database.

[viking9]

I don't think rad alts are used above 2,500 ft.

[jgrloit]

I was just trying to consider alternate information sources, that could be fed into different Transponders - to explain a monitored, alternating height senario as recently seen on my system!!!