This might have been addressed although I skipped most of the replies.
If you engaged him and you shot his wing and he's running........ I finish the kill. 2 reasons: he is not taking his defeat honorably. And the 2nd is some other n00b could try to steal your kill. And ask Skyrock says in his example, he BnZ you while engaged, get him back for being a weakling.
However the exception is if he's low alt trying to get back to the base and I'm above him, I'll let him go awarding the kill to another more deserving, or let the pilot use his skills to land his sortie.