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FR24 is a combination of ground-based radar (both primary and secondary surveillance) and ADS-B data.

TCAS (as I understand it) uses the transponder part of secondary surveillance radar, but with out the bearing/ranging info, as well as ADS-B (if equipped).

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TCAS is interesting but it’s not really relevant here. It’s something that is applicable to the en-route portion of a flight, when both planes are supposed to be separated by substantial distances while in the sky.

TCAS is useless in the terminal environment, like while landing or taking off. If it wasn’t inhibited (which it is) it would be correctly screaming that there are about to be a dozen airplanes too close for comfort every single time it got near an airport.

It’s a system for avoiding mid-air collisions not stuff like this.

My understanding is that when an aircraft is < 1000 AGL the TCAS would be at Sensitivity Level 2 (SL2) and they would still get Traffic Advisories (but not a Resolution Advisory); and only once landed and the pilot turns off TCAS would they no longer get messages?

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