First, very slight correction to the thread, most civilian craft have transponders, not IFF. They're kinda the same thing in practice but transponders just give out a static number, IFF is a cryptographic challenge response.
I don't know how the navy does it when abroad, but anything entering or leaving a sensitive area will generally be on an ICAO style flight plan (entering US ADIZ/TFRs/DC SFRA etc) and it's a simple matter of checking to see if the thing responding with "hi I'm mode c or s (civilian aircraft) 1234" is doing what it should be.
There are also some other sidebands that get used like NCTR which looks at the radar return to attempt to identify the type of aircraft but they weren't well developed in the 80s.
If the aircraft is not responding at all to transponder interrogations you can assume it's hostile and presently attacking you or the pilot is forgetful and didn't flip the switch (choose wisely).
You can obviously put a mode c/s civilian transponder on a cruise missile or better yet fill a remotely piloted 747 full of explosives if you're feeling especially squirrelly and that's totally been done. That's also part of why these events keep happening, everyone's kinda understandably jumpy.
Great answer! For anyone wondering, NCTR is non-cooperative target recognition.
> If the aircraft is not responding at all to transponder interrogations you can assume it's hostile and presently attacking you or the pilot is forgetful and didn't flip the switch (choose wisely).
Unless the transponder is bent, M4 is badly updated for some reason, etc. etc. Better do a RAYGUN call or ask AEW&E to declare.
I don't know how the navy does it when abroad, but anything entering or leaving a sensitive area will generally be on an ICAO style flight plan (entering US ADIZ/TFRs/DC SFRA etc) and it's a simple matter of checking to see if the thing responding with "hi I'm mode c or s (civilian aircraft) 1234" is doing what it should be.
There are also some other sidebands that get used like NCTR which looks at the radar return to attempt to identify the type of aircraft but they weren't well developed in the 80s.
If the aircraft is not responding at all to transponder interrogations you can assume it's hostile and presently attacking you or the pilot is forgetful and didn't flip the switch (choose wisely).
You can obviously put a mode c/s civilian transponder on a cruise missile or better yet fill a remotely piloted 747 full of explosives if you're feeling especially squirrelly and that's totally been done. That's also part of why these events keep happening, everyone's kinda understandably jumpy.