As an example, if you vulch someone who is still rolling down the runway and they simply tumble around and manage to survive to .ef from the plane and end the sortie, you will not get a kill nor an assist. That is to say, if a pilot can manage to 'ditch', then the player(s) who was/were shooting at him will not get anything for that effort.
To get the kill credit, you have to be the one who did the most damage to a plane, at the time the plane reaches its critical level of damage. To get an assist, you did less damage than someone else, while the plane had not reached its critical level of damage. To all of that, the pilot of the damaged airplane cannot manage to ditch.
A plane may still be in the air after reaching its critical level of damage. A pilot firing at a plane which has reached its critical level of damage will not be awarded anything, regardless of all other criteria.
If you feel your kill/assist falls within the current requirements and you did not get any credit, feel free to send us a film of that sortie.
