Ground Vehicles

Hmm… My AIM quote was out-of-date. Here is the 2017:

4-5-7 c. 3. ADS−B is intended for in−flight and airport surface use. ADS−B systems should be turned “on” −− and remain “on” −− whenever operating in the air and moving on the airport surface. Civil and military Mode A/C transponders and ADS−B systems should be adjusted to the “on” or normal operating position as soon as practical, unless the change to “standby” has been accomplished previously at the request of ATC.

Which mentions the entire “airport surface”, not just the movement area.

And according to that SAFO you linked to, it says to leave ADS-B enabled after landing, and all the way up until parked at the gate. And also to enable it before pushback (which would typically be in non-movement areas). So that document seems to contradict itself.

But there’s still the matter of being at the gate with ADS-B. That’s the real debate at hand. I’m having trouble finding documentation (other than your source) that specifically talks about ADS-B at the gate.

On top of that, does anyone know if there is actually a way to disable ADS-B on an airliner (i.e. a Boeing or Airbus)? It is my impression that when a pilot puts their transponder into STBY mode, ADS-B is still transmitting as usual. Perhaps I am wrong.

I don’t think Chris is suggesting that the info be ignored, just that they aren’t counted in the statistics, as it could be thought of as “cheating” for us that live close to an airport. I mean I rose to above #300 in less than a month because of my proximity.

But Chris, I don’t think ADS-B sends out a “FLIGHT” mode indicator in the signal, does it?

1 Like

The transponder must be set to GND on the ground. ALT in the air. Standby is pretty much only used in the hangar/times of maintenance. Part of the cert spec is it must automatically change from ALT to GND after landing and GND to ALT when taking off.

So no, pilots shouldn’t be putting the transponder to standby unless there is a real reason to do so.

1 Like

When set to standby, there is no ADS-B transmission. When set to GND, it transmits, but with the altitude as ground.

That is my intent. I enjoy watching aircraft taxiing but just don’t think that our statistics should be “unfairly” skewed by them.

But Chris, I don’t think ADS-B sends out a “FLIGHT” mode indicator in the signal, does it?

I guess I should have phrased it as not being in “GROUND” mode. :smiley:

1 Like

On some fleets, the transponder circuit breakers, along with a few other breakers, have color coded collars (usually red) which are pulled on completion of the “SHUTDOWN” checklist.

This is done to de-power certain components if the aircraft is going to be left unattended for an extended period of time powered up.

OK, that clarifies things a bit. I’ve been trying to find some info on this “GND” thing for a while. The ADS-D Decoding Guide http://adsb-decode-guide.readthedocs.io/en/latest/index.html makes no mention of it. So I have two(ish) questions:

What input/sensor does it use for determining GND/ALT? I see a lot of aircraft that jump from GND to 25, 50, 75 feet while taxiing (and sometimes at the gate). Once in great while an aircraft will jump up to cruising altitude while at the gate (and at 0kts). Then there was one time I saw 60000ft at the gate! Clearly the later two are errors (the coding only allows for up to 50175 feet), but I don’t see why the first example is reporting a (low) altitude when on the ground. Any thoughts?

Perhaps this is related: How is “GND/ALT” coded in the message? The altitude part can’t just be 0 because that actually means -1000 feet. Again, the Decoding Guide doesn’t specify.

There are two different position message types: airborne position and surface position.

Airborne positions include altitude. Surface positions include track heading / speed. When airborne the velocity is in a separate message. The position encodings are slightly different so that surface positions have better resolution but are not globally unique (they decode to one of 8 possible points on the surface of the Earth - the assumption is you know which one is right based on the receiver location)

There is a somewhat complex set of rules for deciding when to do airborne vs surface position reporting that includes e.g. weight-on-wheels sensors (if present); a-priori knowledge of the type of vehicle the transponder is on; current groundspeed, airspeed, and radio height.

The “60000ft at 0kts” may be an artifact of what the FAA data feed does if you’re looking at tracklogs rather than direct data you received.

Our SHUTDOWN checklist calls for the transponder to be placed in STBY.

Quite intriguing. Thanks for the info.

And the “60000 at 0” was on my own receiver. Only happened for a second or two so I’m assuming just a bug during decoding or something.

A real reason to do so?
Maybe it’s to help you to not transmit the wrong squawk on next startup if the last pilot didn’t clear it out.
But from an FAA (and non-company specifics), there isn’t a good reason. They can add to your SHUTDOWN checklist to “rub your belly 3 times counter-clockwise”, but it isn’t needed for ADS-B to function correctly.

Reason?

I would have to ask the FAA. They are the ones that approve our checklists. No changes can be made to them without their consent.

Ok, approval is not really relevant. They could also approve a list with “count all your fingers before engine start”.
Please do ask the FAA. Or your chief pilot. There is no FAR, AIM, nor AC to back up this as some sort of requirement or SOP for all aircraft. It’s only company specific. Companies can choose what they wish. (Which is perfectly fine). FAA approval doesn’t imply that the FAA promotes or requires that specific task. It only shows that they don’t have an issue with you performing the specific tasks and in the order in which the tasks are listed.

1 Like

I installed the antenna on the control tower roof on a 10 foot mast but I am losing targets within 5 miles or so of the airport and show no aircraft on the ground at all. I am using the FlightFeeder 7.9.1. Any suggestions?

On-airport FlightFeeders usually need to be manually tuned by us to reduce the gain so they are not deafened by strong signals from nearby transponders - this should happen some time in the next few days for your site.

1 Like

I reduced the radio gain to 35 and got my first ground target.

May i humbly suggest that you may be in a high RF environment and might need a filter to decrease the ambient RF noise level. If nothing else it would be a cheap and easy test.

Bob Davis

He is using a FlightFeeder, those have filtering built in.

And losing planes when they are close to you can only mean one thing: signal overload.
So reducing gain is exactly the correct approach.

If the planes are straight overhead at high altitudes it can also mean your antenna has a blind spot there (mine does but it’s not very big). But for planes on the ground that’s a non-issue.

Regarding an earlier comment in this thread about different graphic for ground vehicles.

Strangely, on FR24 they appear to show ground vehicles at Gatwick as a different graphic but can’t see this repeated at Heathrow, Luton or Stanstead.

Geffers

“He is using a FlightFeeder, those have filtering built in.”

So your saying he “can not” or “may not” benefit from additional filtering?

And the correct answer is “may not” because “can not” has not been the case with the FA filter and the blue dongle for my location. I have aircraft fly directly overhead(I mean stand under my antenna and look directly up at the belly of the plane) at 2000 feet with over -2 DBfs and they still register fine (FA Antenna). All this happens with gain set to default (AGC)
And that is exactly why I use AGC. At the airport you have aircraft landing and taxing with ads-b on full and you are still trying to hear a truck behind a steel building on the other side of the airport…

I would think that being on the top of the control tower at the airport that gain would not be issue except if there is too much signal. So maybe we should try filters to block out some of the other interfering signals that overload the front end of the receiver. Of course you need to check the connections and cables, etc.