The only 'loop' that I am aware of that was tried in a transport aircraft was an AA (if I recall correctly) DC-4 just west of KELP, many many years ago.
A deadheading pilot reached down and applied the gust lock during cruise-climb...and the aircraft was 'bent' beyond repair.
Airline flying is a wonderful way to make a living, but every once in awhile, you find some jerk that is just not satisfied with operating the normal way, and wants to experiment.
For these I say...a pox be upon 'em.
