Hacker News Reader

Comment by knz | Hacker News Reader

This assumes that surveillance aircraft have their ADS-B transponder on. It's not required until January 2020 (https://www.faa.gov/nextgen/programs/adsb/faq/).

View on HN

Running without ADS-B around major airports would be unacceptable. I think drones are going to be required to have them before 2020 which makes me think that isn't quite right.

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.

I track several of these aircraft a week, and they usually don't have ADS-B. I track them via multilateration, combining my receiver's data with data from several other receivers (as part of the Flightaware network: http://flightaware.com/adsb/)

Many commercial operations don't have ADS-B installed (I wish! That would make my life easier.). They use other systems like MLAT and primary radar to track them.

If they make drones carry ADS-B transponders, it will only be heavy and high-flying drones. Signal becomes noise after so long, and they don't want to overcrowd 1090MHz.

How would traffic controllers handle them over US or busy cities? Just see them on radar, would they know that this object is not someone drone? Or would they rely on matching with a flight plan and expect it.

I work at a large airport near where these operations have occurred. From what I understand the local FAA office is well aware of them. I've been told "Don't ask" when we see unusual flight patterns. Commercial aircraft tend to follow well established patterns (STARs and SIDs etc) near major airports. As long as these flights stay below certain altitudes and away from the arrival and departure paths I don't think it would be a big deal for ATC.

As long as these flights stay below certain altitudes and away from the arrival and departure paths I don't think it would be a big deal for ATC.

Exactly. Police helicopters fly low enough that unless they are on the final approach or departure path, its not a big deal.

Its a common misconception that because news helicopters following the chase are denied clearance to fly near an airport, the same would apply to the police helicopters.

Oh ok, makes sense. Thanks for explaining

Reply on news.ycombinator.com