Hail damage to American's airliners in Texas

[Phil Bunch]

News story here re this hail damage American Airlines and its regional airline(s) have experienced:

http://www.bloomberg.com/news/2012-04-05/american-eagle-cancel-flights-for-third-day-on-hail-damage-1-.html

Unlike an automobile, my understanding is that an airliner can't be used if it may have acquired even slightly damaged or dented sheet metal.  

I wonder how they determine if these airliners have experienced sheet metal (exterior skin of the aircraft) damage after a large hail storm?  Do they have to perform x-ray and ultrasound or other tests on every exposed surface?  I wouldn't think that it would be good enough to just look at the aircraft and visually judge if the exterior surfaces and panels look a little dented.  There must be a zillion external sensors, ports, and antennae, that must be inspected, too.