Comment by neurotech1 | Hacker News Reader

Comment by neurotech1 | Hacker News Reader

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With ATC notified, the helicopter could revert to Mode-C [0] transponder mode, using an assigned transponder code and ATC would still track them safely. TCAS [1] would also still function safely when interrogated by secondary radar.

ADS-B reduces controller workload as they don't have to manually tag individual aircraft, especially in a high traffic area. ADS-B also works without secondary radar interrogation.

When there is a high speed chase near an airport, sometimes the tower controller will request the helicopter remain under a certain altitude or clear of a specific area.

Additionally, websites like FlightAware.com have limited direct ADS-B coverage and also display the FAA 5-minute delayed feed. I've never heard of a "criminal" in the US using an ADS-B receiver to evade police helicopters in real time.

[0] https://en.wikipedia.org/wiki/Aviation_transponder_interroga...

[1] https://en.wikipedia.org/wiki/Traffic_collision_avoidance_sy...

Flight aware just announced real-time flight tracking data (US & Canada). [1] Also, they will be adding MLAT data. (US)

[1] https://flightaware.com/news/article/Realtime-Flight-Status-...

I wonder if a $12 TV Tuner RTL-SDRs can listen in to secondary radar triggered TCAS responses? (I wonder how much trouble you'd get in for setting up a USDR or HackRFOne to transmit your own "secondary radar" signals to make the TCAS respond?)

TCAS "responses" are only sent during a Resolution Advisory.

Mode-C and Mode-S responses are sent when interrogated by secondary radar. ADS-B transponders with "Extended Squitter" transmit regularly while active, so no need to transmit your own interrogation pulses.

Its possible to monitor Secondary Radar pulses, and Mode C returns. It would require multiple geographically separated receivers to triangulate. I don't think FlightAware supports Mode C, only Mode S(MLAT) and ADS-B.

If you transmitted your own "secondary radar" pulses, the FAA and/or the FCC would probably launch a criminal investigation, with the FBI involved. Making your own "secondary radar" would be pointless and high risk.

Interfering with radar equipment by transmitting in a controlled, safety and security critical band? On a bad day, that could land you a truckload of terrorism charges.

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