Bomb craters should behave like debris. That is, planes and vehicles shouldn't be able to drive over them w/o damage (or in the present case, blowing up).
This is an
excellent idea; with all the complaining about level bombing being ineffective against airfields. Have the craters appear on the ground where the bomb hits, and cause
X amount of damage to the landing gear of a plane that tries to taxi across the crater. Past a certain point, though, the crater would be deep enough that dropping a gear into the crater would be enough to tumble the plane and destroy it.
A picture of a Stuka attack against a Polish armored train, dropping a single 550-lb bomb:
You can estimate the crater size from the track guage and the people standing to the left of the train.
From estimates used by the US Air Force for its dropped ordnance, a 250-lb GP bomb can be expected to make a crater about 10' in diameter, a 500-lb bomb a crater about 15' in diameter, a 1000-lb bomb a crater about 35' in diameter, and a 2000-lb bomb a crater about 50' in diameter. The depth of a crater is roughly half the crater diameter.
Of course, it would be necessary to add ground repair to the field rebuild process. It would be simplest to abstract it so that a crater of size
X would be repaired in
Y minutes, with each field size being able to repair a different number of craters at the same time (i.e., bigger fields have more people to work on repair). There should also be a drivable repair vehicle -- some sort of bulldozer would be perfect -- that could ignore the effects of driving across craters, and that would repair a crater by driving across it a number of times dependent on the crater size.