The idea of a 'valid' kill is essentially an assumption based upon some reasoning and evidences. A 'confirmed' kill is when there are eyewitnesses of the event, something that often occurred back in WW II when air combat were always within visual range. A 'valid' kill is when we declared that based upon A, B, and C, there is a greater than %X probability that the target did not survive. A 'valid' kill can be updated to 'confirmed' if later there are forensic proof that the target did not survive. These proofs can be something like debris or ops logs that said the pilot did not return.
Chaff can mislead a missile, even an AMRAAM or any claimed to be 'the best' missile out there. There are several related issues here.
When a missile is classified as 'fire and forget', it does not mean launch and leave. On the whole, we, meaning the entire military aviation community, did not have a good record of such a missile, even when we did designed and deployed such a missile. The 54 Phoenix was not only 'fire and forget' but actually 'launch and leave'. The Phoenix was not an 'integrated' weapon system precisely because of the 'launch and leave' design. Once launched, the pilot is free to leave the missile to its own devices. The missile carried its own active radar, discriminate its own target, select for home, and boresight on a target. The Phoenix's concept made the missile large, heavy, and time consuming for maintenance, especially for the electronics, which was not upgradable and
rapidly getting older as miniaturization progresses. So when the F-14 retired, the Phoenix system had to be retired as well.
So where does the phrase 'fire and forget' comes in?
Experience showed us that the longer the ranges the greater the odds of a failure to kill. The longer ranges requires the missile to have as much data as possible in order to do what the Phoenix was designed to do: active radar, discrimination, selection, home, and boresight. The more radar activities, the greater the odds of the target being aware of the missile threat, especially when the radar operation changes to boresight mode which produces intense and unique signal characteristics, which the target would confirm to itself that there is a missile threat. But if we reduce the range on when to launch the missile, we risks getting involved into a turning fight which despite the romanticism of WW II, no pilot want to get into such a fight in the first place.
The compromise is the somewhat arbitrary designation of 'mid range' which for the AIM-120 started from 50 km and now to 150 km which approaches the 190 km of the Phoenix. So much for 'mid range'.
To increase the odds of a kill, or given the range involved, at least a 'valid' kill, we have to sort of 'silence' the missile's own radar operations to the last possible moments. To do this, the AMRAAM's radar does not 'go active' until certain algorithmic solutions are satisfied, and these are secrets. Suffice to say for public discussion, that 'go active' point is generally the mid point between the launch location and the target's location.
For example, if the distance between launch and target is 100 km, the AMRAAM's radar will go active when it crosses the 40-50 km point. Less if the launch aircraft decides to continuously guide the missile instead of the missile using its own radar.
When the AMRAAM's radar is active is when the missile becomes a 'fire and forget' weapon because it is calculated that the target do not have sufficient time and distance to formulate any countermeasure, even if his radar warning receiver (RWR) alerted him to the missile threat.
This goes back to the statement that declared chaff cannot mislead the AMRAAM. Chaff can mislead the AMRAAM depends on when the missile was launched, when the parent aircraft severs its guidance, and when the AMRAAM's radar go active. The longer this distance, the greater the odds of success for chaff. If a pilot launched an AMRAAM at max or near max operational range and immediately abandons it, chaff WILL mislead this AMRAAM.
This is why modern air combat is no less mentally challenging than when pilots fought with guns at several hundred meters apart. The pilot must know his aircraft and weapons limits in order to create as ideal as possible the environment for the missile to succeed.
The AMRAAM have a proximity fusing system that detonates the warhead without the missile impacting the target. Proximity fusing increases the odds of a kill.
