>>>Could a moderate dent cause an aircraft to not be airworthy? It appeared to be about 5-6 inches long and a quarter-half an inch deep. And, what would
UA do with this plane?
It depends. I'll leave it to the AMTs here to cite chapter and verse, but generally speaking, if the metal is torn through, or rivets are popped, or stringers are busted, the aircraft is out of service until it gets repaired.
If such major damage occurs at an airport where the airline doesn't have its own
MX personnel, it's quite common for the airline to ferry the aircraft to a location where repairs can be made. This is done under a maintenance ferry permit, which means no passengers or (usally) no FAs aboard. In the case of fuselage damage, that also means the maintenance ferry flight is operated unpressurized, which can man some long flights at 9,000 or 10,000 feet enroute to the
MX base.
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.