FlightAware Discussions

Tracking local Police Helicopter on my own piaware

I use to be able to see our local police helicopter activity on my local Piaware box by going to its local IP address. Something has changed in the last several months and I am no longer able to see its flight paths. My understanding is that with my local PiAware box, I could see ALL traffic (even hidden traffic), but that the hidden flights wouldn’t show up on the aggregated public “FlightAware” site. Does anyone know what might have changed (either with my setup or the aircraft). The tailnumber is N408PD. Thanks

On your local device there is no filtering. So you are able to see all aircraft where the transponder is active and signals are received.
The filtering is done on FA side and should not impact your local view.

Be aware that in some situations the transponder is turned off. Or it could simply be that the helicopter is not in range of your receiver.

You could cross-check on ADSBExchange, they are using unfiltered data.

Thanks for your reply. I know the helicopter is within range as it was circling less then 2 miles away supporting police activity. And I live in a large city where it would be “unsafe” to turn off an ADSB transponder. I am wondering if perhaps there is some different technology that they are using. Less then a year ago, I could see all of their flight traffic.

The helo could have changed over to UAT. Do you track UAT?

Also, they could have turned off their transponder for operations reasons. They can work with ATC directly to ensure that there are no traffic conflicts. ATC can give them a blanket area to operate in.

Thank you for your reply. I don’t believe I track UAT. I am somewhat of a newbie and use that standard PiAware install on a Pi Zero. Is tracking UAT possible with the same install? Is there a way I could check if they use UAT. I am not thinking they turn off their transponder as I don’t see it flying at all throughout the day. Thanks

UAT requires another dongle and antenna.

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Pretty sure it’s not UAT as suggested.
Actually i think they went to a ModeC transponder which is somewhat impractical to do MLAT for and also you only get the sqawk and not an icao hex.
Thus it’s not displayed “without position” either.

Tracking ModeC is really annoying.
They operate with visual separation to other traffic anyhow so it’s perfectly plausible.
I’m not sure how well ModeC will interact with airliners equipped with TCAS but hey.

The last flight i see for that airframe are over San Jose … i’m positive there is good UAT coverage there for the resource i’m using at the very least there would be intermittent positions.

Are you certain the N number is still the same?

Law enforcement is allowed to turn off position reporting for “sensitive” operations. If you’ve seen it on 1090 ADS-B before then it may have just turned off position reporting.


Pretty sure this is not considered as unsafe if there is a strong need to turn off ADS-B.

I live in San Jose and was also recently looking for N408PD. I followed it a few times with TIS-B, each day with a random icao. The icon appears as a small plane locally in tar1090 and the reported id changed each day. The way I guessed it was N408PD was correlating the orbiting pattern with areas with reports of police activity reported on nextdoor.com. I have not figured out a way to identify it reliably.

  • 1-18-2021 icao ~2b00cd (TIS-B)
  • 1-20-2021 icao ~2b0f15 (TIS-B)
  • 1-21-2021 icao ~2b0c35 (TIS-B)

Is this what you mean by Mode-C? I’m just learning how this works. Thanks.

Well what you see is TIS-B … some explanation in the details on the left.
All TIS-B means it’s ATC somehow knows the location of that thing and broadcasts it.

But one can assume it’s ModeC (because with ModeS there would be MLAT).


And ADS-B is mostly ModeS with positions and more details.

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Thanks Mike. I am a total noob at this. I always had entered my local PiAware ip address and PiAware. I don’t know what TAR1090 means but I see a menu choice called TAR1090. Perhaps I should start looking on that tab. I’ll search more on the web for details but do you have a brief descripton on what the PiAware menu button will give you vs “Radio 1090” button?

Tar1090 is an enhanced web based map interface. Take a look here if you want to upgrade:
GitHub - wiedehopf/tar1090: Provides an improved webinterface for use with ADS-B decoders readsb / dump1090-fa.

When searching for aircraft that you suspect should be there, also double check the adsbexchange map. They show flights regardless of the blocking status. All the other flight trackers remove flights and filter out data before you see it.

It’s still the same data. (well there is a website using it for global data but talking about the local interface here)
The screenshot … kinda complicates that … i should annotate when it’s the online feed map for a specific receiver vs global data. (screenshot … is basically a local interface but served remotely)

About a week ago in my area of town, I kept hearing a helicopter flyover my house, looking on my radar page I could the helicopter and was able to determined it’s tail number, using that I could see that it was being operated by the Jacksonville Sheriff’s Office, I found out the next day there was a SWAT standoff for 14 hours in the neighborhood next to mine…

I see regularly two helicopters in my area spraying the wineyards.
They are visible on my local ADS-B only once in a while.

It’s not my device as other low flying aircraft with similar distance are showing up all the time.

Thanks for the pointers, that helped. I think I understand now, but please correct if I am off here.
The helicopter could turn off their ADS-B broadcast and switch to using Mode 3/A and 3/C which is less identifiable.

During flight, ATC somehow knows their position, possibly from their ground radar combined with Mode 3/A 12-bit squawk identifier and Mode 3/C 12-bit altitude responses from the helicopter. ATC nicely rebroadcasts this data on TIS-B so other aircraft know the location of the helicopter to avoid in congested airspace.

Because the helicopter now only uses a 12-bit temporary identifier when interrogated in mode 3A/C, the ATC rebroadcast only sends 12-bits of identification in the icao 24-bit id field. The upper 12 bits are just a fixed number. The temporary 12-bit identifier can change every flight so no easy way to track the helicopter across flights using the identifier.

I should have uploaded the SkyAware screenshot instead. On my local machine, SkyAware plotted mostly the same data. tar1090 is just a preference.

Without identification, there is no guarantee this is SJPD N408PD, that is just a guess based on reports on the neighborhood watch site. It could also be the Sheriff helicopter or anything else.

I wouldn’t jump to that conclusion … i’m not sure how the TIS-B 24 bit ids are made there are no rules regarding it … each ATC system can implement it as they want.
But with the 2b0 not changing it’s not a terrible assumption i suppose.

Well i meant because you didn’t use your local tar1090 (which has better track resolution than the online feed map by the way).