Some bolts have drilled heads for a reason: They are supposed to be safety wired. The first example is a wheel pant bracket. The left wheel pant bracket on this airplane was missing the safety wire. A discussion with the builder ensued until the right wheel pant was removed—that bolt had gone missing!
The second example is a prop governor screw. Should it come loose, the prop could overspeed, potentially necessitating a teardown of the prop and/or engine.
