Mode C and MLAT tracking

Can non ADS-B equipped aircraft be tracked via MLAT if they are only operating with a mode C transponder? According to this page a mode S transponder is required in order to calculate MLAT yet I see aircraft being tracked that only have a mode C transponder. How is this possible?

Yes, but only if they are squawking a discrete transponder code and there are receivers in range that send Mode C data to Flightaware.
The Transponder code would need to be reconciled with the FAA(or local agency) Flight planning to match it with an aircraft.
Turn on “Show position-only flights” in Section 6 of your "My Account " settings to see them.

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Does a piaware install track mode C data? I’m assuming mode C data is transmitted on 1090MHZ?

To clarify, say for instance an aircraft is squawking VFR (1200) with no flight plan filed and there are receivers in range. Only that aircraft’s position is tracked correct? In short, you’ll see an aircraft flying around but won’t know which aircraft it is.

Now let’s say an aircraft is squawking VFR (1200) with no flight plan filed but requests flight following and is assigned a discrete transponder code for a portion of the flight. Is the whole flight tracked or only the duration of the flight where a discrete transponder code was in use?

Lastly, how does reconcile a transponder codes to aircraft?


Piaware can track Mode A/C, however, most feeders do not.

It is very hard to track VFR/1200.
Mode C will differentiate the altitude, however, it is easy to have multiple aircraft at the same altitude. My training aiport, YSBK, could have 6-8 aircraft in the training pattern at one time (I think they limited it to 4 or 6 at night). 3 or 4 could be at the same altitude on Downwind.

Also, my radarcape gets up to 6000 Mode A/C packets per second, when Mode A/C is enabled(I don’t have it enabled at the moment). That is a lot of information to try to sort out, from just one device.

Most devices don’t do Mode A/C.

I think that all those A/C-only flights are listed as “Other”. In my area those make 25-30% of the flights (lots of military).
AFAIK FA doesn’t process the decoded A/C packets, even if it’s enabled.

If there is a hex code in the column “ICAO” then it’s a ModeS equipped aircraft.

ModeS equipped aircraft can also answer with ModeA replies depending on the interrogation i by the radar i believe.

I just switched modeac on and checked with
view1090-fa --modeac

So i have not a single aircraft in range which is only Mode A or C.
All are ModeS also being displayed with A and C.

Where do you see tracked aircraft with mode c transponder only? (On the FA website it might be data from ATC)

Something from wiki: (Aviation transponder interrogation modes - Wikipedia)

Ah, they all have that. There are many without Squawk.

FlightAware’s ADS-B network does not track Mode A/C-only aircraft. PiAware can be configured to decode this data if you want, however it is not particularly useful for tracking. Among other issues, some Mode A/C replies are ambiguous and cannot be distinguished between an altitude reply and a squawk reply.

FlightAware MLAT calculations are only possible for Mode S-equipped aircraft with their unique ICAO24 “hex code” assigned.

FlightAware’s free flight tracking on incorporates not only ADS-B and MLAT but many other sources of data including data directly from air traffic control. It is possible to track Mode C aircraft on when we receive position data for the flight from air traffic control. Ensure that you have “position-only flights” enabled in your account settings to see these flights.