They are in the Joly Green Giant, right? Does that even have skids? In my hazy memmory, I remember JG's being towed about. Maybe I am wrong. Skids have way more friction than tires and to save weight, I do not think one would have both. I do not recall the landing gear being retractable. But, there could easily be many models.

Buzzing the Base, Unless Coast Guard Choppers are a common occurance at Ft. Irwin, I think it would generate a recognition response from an intelligent human. I do not think the average dumb zombie could "fake it".

Radio. There are a hell of a lot of channels on the radio, but unless someone %^*&(%^&* with the radio it should be on a marine (oceanic not as Burt) emergency channel. I do not know military protocol for emergencies. But, I would think chopper would be remain stationary with the base the oblication to tune to the proper frequency.

Like Crowbar states, I take the tied down choppers as the base is / was controlled. A zombie panic would probably have them moved. But, if the initial zombie assault is repulsed valuable assests would be protected as per standard operating proceedures.

We hear them say they see "people" The number of people must be low or they would not land. If the number of survivors on base is low, I can see them spending much time in lock-down as was done in the tower. A few zombie doing the Ikky Shuffle would not be a concern. Pegs did not spend much time circling, so if there are reinforcements I would expect them to come from the buildings soon, but can accept not yet.

I can see the tension after the zombies are killed and the humans come out. Datu Draws down on them, shoots, misses. The people shout, Don't shoot we're alive! Then according to all my ol' drinking buddies I have to drink because of reference to the title....