MLAT Blocking Specific Aircraft?

Looks like the president is returning from Europe and over flying New England toward DC. I’ve been watching my local VRS instance and this is the only MLAT flight that hasn’t resolved a position. Has Flightaware recently implemented MLAT blocking for this flight? I recall being able to track it in November.

Many (military & private) flights have their details blocked - it would be no surprise if that included AF1.

Does AF1 even have Mode-S?

A lot of military planes are just the old transponder (Mode-A/C).

It’s my understanding that MLAT here is Mode-S only.

Monday I picked up 5957 Mode-S messages from AF1…this was the only a/c whose mode-S did not resolve position via MLAT. The same a/c did provide a track in November and December. Further, I see plenty of private and military a/c on my personal VRS instance; I can watch the refueling tracks over New England from Mode-S -135s as they tank Mode-S C-5s and C-17s.

It doesn’t matter, it was an interesting observation…and I suppose those that know the answer are unlikely to share.


Same for me… on monday I got more Mode-S messages.

Well, I guess I was wrong then. But who really cares where AF1 is?

I’ll go out on a limb and guess that at least the First Lady and few folks in the government care where AF1 is. But using your rationale - why are any of us here, who cares where any aircraft is at any given time? ATC has tracks on them, call the airline to know whether your flight is delayed or canceled.

It’s a hobby, it’s interesting.

PAX River has been flying a P-3 on low level flights over the eastern panhandle of West Virginia. I have an ADS-B setup but only using the small antenna. However, I can get flights within about a 25 mile radius. I see commercial flights but I cannot see this P-3. I’m new to this and it seems either they are using something else, or that their data stream is being blocked. I can hear the flight overhead but cannot see its blip.

Any thoughts? Thanks

In the UK, military traffic flies under different rules to civilian aircraft and so do not always have transponders active. I have seen RAF Typhoons flying nearby, but not had any reception at all from them yet at other times they do appear.

In Germany it’s the same… They switch off their transponder and you can see nothing on your screen. Also often seen while refuelling operations.

Thanks for the responses guys. I appreciate them. I suspect a similar thing occurs over here in the States. I will do some more research and see what I can find.


It is not that the military aircraft turn off their transponders, but they have their own military modes. … tion_modes


When refueling the receivers usually “strangle” (put in standby) their transponder and radar. In the states, the ATC gets conflict alerts, so the aircraft lead will squawk, and everyone else in the formation will “strangle”. You can hear them on the radio by saying “nose is cold”.

If the flight gets into combat, they all un-strangle, so the Air and Ground surveillance radars can sort out the targets.

Also ATC can assign a block altitude that the military takes responsibility for (MARSA) and all the alerts are suppressed.

There’s still a lot of military with Mode-1,2,3,C,4 (SSR) only. The B-1, B-2, and B-52 for example, have no Mode-S. You won’t see these guys unless you listen to Mode-3. Mode-3 for example, doesn’t really know if it is Mode-2 or 3, they both look the same on a passive receiver.

Planeplotter has a altitude view where you can see SSR Mode-C tracks. None are associated with Mode-S, but I could watch B-1’s take-off and climb, or do touch and go’s. Alas, I no longer use Planeplotter (no Windows).

Interesting. I would have thought that entering combat, all transponders would be turned off so as not to alert the enemy or give them any more information than necessary?

Adding the capability to display and track SSR Mode-C targets (I assume only possible if on unique sqwak codes, ie. not 1200) would be a great addition to dump1090.

dump1090 has --modeac which will do what it can to demodulate mode A/C, it’s only really visible via --interactive though.

Can you use that to multilaterate positions on Mode C traffic though?

The squak code could be used instead of the ICAO hex used for Mode S MLAT.

As far as I know, only bombers do that. Fighters need all the help they can get. They usually just squawk Mode-1,2, and 4.

In the Gulf war, the bombers all flew to special points, so if they were headed to that point and radar only, we didn’t blast them.

I’m sure it’s harder today, with most forces having sophisticated ESM gear. I saw some of the Czech products at Red Flag, and was impressed at seeing all the targets passively.

You could use it for multilateration, but neither the FA system nor the github version do that currently.

Thanks again. Looks like I have a few more things to read up on.

And why does my dump1090 get Mode A/C messages from network client? Usually I get Mode S messages from network client (must be input from fa-mlat-client)