Why no MLAT for mode A/C?

Why can't we use MLAT for mode A/C aircraft? That would cover nearly everyone who isn't required to upgrade to ADS-B (i.e. not flying in airspace that requires it) as well as GA aircraft in the US who are using UAT/978 rather than 1090ES without the need for separate 978 feeders.

I assume it would only work for those with a discrete squawk, but we'd be able to track VFR in busy terminal areas, which is where we have decent MLAT coverage anyway, and perhaps some rural folks with flight following if they're high enough--plus all IFR aircraft.

 

Mode A/C doesn't broadcast transponder hex, only altitude and ATC squawk code.. There is no way to tell what it is and relate it to what it is.

https://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes

ADSBx images decode them, but they just aren't useful.

 

We wouldn't know who/what the target is, but we'd still see that something was there, which seems like potentially useful data. Anyone who doesn't want that data can easily filter it out, right?

 

No. You don't know who it is. All Mode C broadcasts is squawk code and altitude.

 

Tha MLAT calculation (to my knowledge) is based on the unique Mode-S hexid. With Mode A/C there is only a 4 digit octal code. That wouldn't be a problem because you can create a fake hexid consisting of FF and the squawk code. Unfortunately the squawk code is not unique to a plane and only unique in a relatevely small area. So it can't be used centrally to calculate the position.

 

Yup. the only way to know the 'who it is' is mode-s ...

In the US we can piggy back off the 978 UAT towers if the aircraft in questions is talking to ATC ...

 

So I'd say it *would* be possible to assign them a fake hexid FFoooo and see them on the map if you setup an own MLAT network in your area. Of course you need other tricks to assign them to real planes. How about machine learning and extracting the information from ATC radio

FunFakeFact: A/C means Anonymous Coward

 

Squawk code should be unique within an ARTCC (US), and I'd assume ACC elsewhere, which is a pretty large area. Couldn't the MLAT software be tweaked to not correlate reports from stations over N miles apart?

 

Theoretically .. but in practice that would require a lot of coding that is far beyond my skill set.