Killshooter=2 hitting ANY plane causes shooter to receive the damage.
Now, why would you want such a mode?
Here's an age-old scenario problem:
If all planes in flight at frame end are scored as having landed, experience shows that some people will stay in their ditched aircraft, or keep their hopelessly damaged craft aloft behind the end of the frame. Moreover, in multi-sortie scenarios, one could for example plan a last minute bombing sortie without worrying about fuel for the return leg -- and last-minute fighter intercepts would have to destroy the bomber, not just kill all the engines.
But if all planes are required to land at the end of the frame, the CM has to call an end to the hostilities before that time, and that rarely occurs without incident.
That's where such a killshooter setting comes in. Making any shot that landed hurt the shooter would certainly discourage folks from dogfighting after the buzzer. Then everyone could try to RTB. YOu could even use this to encourage reasonable scenario behaviour by turning it on for the last ten minutes, then counting everyone not exited as lost.
Anyway, it's just a simple suggestion for something easy to implement that would give the CMs greater flexibility in designing and executing scenarios.