[Goose]

It's possible that the flares and chaff both deploy at same time as a countermeasure on the A-50, we're only able to see the flares.

Could be. If the target A-50 detected the missile but held no missile guidance radar, using both makes sense. It may be an infrared missile, in which case the flares are the only countermeasure. It could also be a radar guided missile that for unknown reasons was not detected by the RWR/ESM system. In that case chaff would make sense, but since you don't know, you use both. Some countermeasures systems do indeed take the "do both" approach unconditionally. I would expect an A-50 to have a better capability. Certainly if it was a Patriot missile the A-50 should have detected it with their own active radar early enough to know what it was and not bother with flares. They may not have passively detected it's guidance radar (though they should have), but they would know by it's long flight profile it was radar guided. If it was infrared they should have detected it with their radar before it hit them, but not by too much. That kind of matches what we see in the video.

But the operators knew something was lighting them up in any case.

Not necessarily. The active radar on the A-50 is the primary sensor. The A-50 also has RWR/ECM capability, but that is a secondary sensor. Infrared Missile Approach Warning (MAW) basically doesn't work very well. It is OK if the rocket motor is still burning (or you detect the launch), but after that it isn't very sensitive. The front view of the missile doesn't radiate much heat.

Another possibility would be a shorter range takedown by some sort of commando force behind enemy lines with a IR missile. The Ukrainian Air Force and Intelligence Department jointly claimed credit.

IMO that scenario fits the known data much better. I am not sure of the location/geometry, but it appeared to that the A-50 was operating at a relatively low altitude, as if it was just starting or ending it's mission. Most IR missiles are relatively short range, which seems to match what happened.

[Goose]

It's possible that the flares and chaff both deploy at same time as a countermeasure on the A-50, we're only able to see the flares.

Could be. If the target A-50 detected the missile but held no missile guidance radar, using both makes sense. It may be an infrared missile, in which case the flares are the only countermeasure. It could also be a radar guided missile that for unknown reasons was not detected by the RWR/ESM system. In that case chaff would make sense, but since you don't know, you use both. Some countermeasures systems do indeed take the "do both" approach unconditionally. I would expect an A-50 to have a better capability. Certainly if it was a Patriot missile the A-50 should have detected it with their own active radar early enough to know what it was and not bother with flares. They may not have passively detected it's guidance radar (though they should have), but they would know by it's long flight profile it was radar guided. If it was infrared they should have detected it with their radar before it hit them, but not by too much. That kind of matches what we see in the video.

But the operators knew something was lighting them up in any case.

Not necessarily. The active radar on the A-50 is the primary sensor. The A-50 also has RWR/ECM capability, but that is a secondary sensor. Infrared Missile Approach Warning (MAW) basically doesn't work very well. It is OK if the rocket motor is still burning (or you detect the launch), but after that it isn't very sensitive. The front view of the missile doesn't radiate much heat.

Another possibility would be a shorter range takedown by some sort of commando force behind enemy lines with a IR missile. The Ukrainian Air Force and Intelligence Department jointly claimed credit.

IMO that scenario fits the known data much better. I am not sure of the location/geometry, but it appeared to that the A-50 was operating at a relatively low altitude, as if it was just starting or ending it's mission. Most IR missiles are relatively short range, which seems to match what happened.