I find it rather idiotic to first have an aircraft spend 2 weeks in C check, only to go straight to D check for another 60 days. So, could the game check before it puts a plane on automatic C check, that the D check is not coming up in less than, say, 4 months. And if it is, send a message to the player saying that you might wish to send it straight to D check and skip C check.
Couldn't find any decent information, if C check is included in D check. If it's not, then this feature would change nothing...Here
's some discussion about the matter.