I just notice an alert on my display flash about not contacting authorities about a squawk,
It flashed fast and didn’t get to read it all. I started looking up for squawk codes, 7700,7600 and 7500.
I looked through my logs and found three 7500 codes from an aircraft close to me. What exactly does this mean?
Those transponder codes are reserved for emergency situations, and will produce an alert with ATC when seen - that’s why it says don’t contact the authorities as they will see it straight away.
From the ICAO procedures document:
8.5.2.1 Codes 7700, 7600 and 7500 shall be reserved internationally for use by pilots encountering a state of emergency, radiocommunication failure or unlawful interference, respectively.
If you saw 7500, it was likely an error by someone setting the transponder or a bad decode, especially if it was only briefly shown.
./history_3.json: {“hex”:“ac56cf”,“alt_baro”:32000,“squawk”:“7500”,“mlat”:[“nac_v”],“tisb”:,“messages”:3285,“seen”:0.1,“rssi”:-14.1},
./history_4.json: {“hex”:“ac56cf”,“alt_baro”:32000,“squawk”:“7500”,“mlat”:[“nac_v”],“tisb”:,“messages”:3433,“seen”:0.1,“rssi”:-9.6},
./history_5.json: {“hex”:“ac56cf”,“alt_baro”:32000,“squawk”:“7500”,“mlat”:[“nac_v”],“tisb”:,“messages”:3617,“seen”:0.1,“rssi”:-5.9},
That’s strange, especially how many messages were in between.
This should be the flight? On FR24 the squawk never changes:
https://www.flightradar24.com/data/aircraft/n8942a#2212cf72
Could also be that the aircraft is only transmitting in a certain encoding and that encoding may be misinterpreted.
I’m really not sure.
You’d need the raw output from
view1090-fa --show-only ac56cf | grep --line-buffered Squawk -B10
Note the hex id after the show-only. You can also search for other sings (instead of “Squawk”) or just show all messages from that plane.
Sample output:
*28000800170a65;
CRC: 471eab
RSSI: 0.0 dBFS
Time: 27186368452.92us
DF:5 addr:471EAB FS:0 DR:0 UM:0 ID:2048
Survelliance, Identity Reply
ICAO Address: 471EAB (Mode S / ADS-B)
Air/Ground: airborne?
Squawk: 1000
--
*28000b32042196;
CRC: 471eab
RSSI: -7.2 dBFS
Time: 27190374601.33us
DF:5 addr:471EAB FS:0 DR:0 UM:0 ID:2866
Survelliance, Identity Reply
ICAO Address: 471EAB (Mode S / ADS-B)
Air/Ground: airborne?
Squawk: 3541
That wrong squawk decode of 3541 showed up mutliple times.
So maybe there is an ambiguity or bug in the squawk decoding.
How does the hex convert to a flight or indent on FA?
The hex is a unique hexadecimal ID for the airframe: https://en.wikipedia.org/wiki/Aviation_transponder_interrogation_modes#ICAO_24-bit_address
It identifies that airframe.
The squawk is broadcast via ADS-B, FA gets that for example via your receiver.
But i don’t think FA even displays the squawk on their website.
As you see with the link, some other tracking websites and your local webpage do show the squawk.
Now the decoding might be done differently depending if for example the fr24feed client does the decoding or for you local map dump1090-fa does the decoding.
view1090-fa uses the same decoding logic as dump1090-fa.
The decoding is not always straight forward as the ADS-B broadcast is often meant for ground stations which interrogate the transponder and thus have more data available for error correction.
In regards to FA, you can’t put in the hex id and get the aircraft i think.
At least not via the search field.
Most of the 7x00 codes, particularly 7500, you see in the wild are errors (pilots dialing another code, bad decodes, etc).
Agree with @mduell! During my time deployed on ships, we would see this on a fairly regular basis and it was never a legitimate problem.