It can buckle.

But if it can be seen to buckle then sometimes the choice is to keep it below buckling. Not always about the airworthiness requirements.

agreed, elastic buckling is allowed at less than limit. Certification requires loads with and without pressure. Clearly, a pressurised fuselage is not going to buckle, so we're talking unpressurised which is somewhat artificial ... but a certification requirement none the less. This (elastic buckling at less than limit) also applies to unpressurised fuselage (like tailcone, aft of rear pressure bulkhead). The important thing is to show a margin between limit load and the "onset of permanent buckling".

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

Yes, diagonal tension is allowed on fuselages; typically buckling is kept above fatigue load levels (less than Limit).

And yes, pressurized fuselage skin panels can buckle, and do buckle at high enough maneuver loads. And "unpressurized" load cases occur at ground level and can be critical, eg. hard landing cases.

Postbuckling analysis is required and can get quite complicated.

Hi ChasGen61

As the other replies you received, yes fuselage structure is allowed to buckle so long as it is not permanent. That being said, on commercial fuselage can tend to happen around 60% of limit. So it can occur at fatigue stresses. Also, pressurization does not entirely prevent buckling. In fact, nasa under the aging aircraft program back in the 90s did extensive studies on this and showed that buckling could still occur under pressure. It depends on the type of stringers, frames, pitch, ect of the panel. There is a good AIAA paper on this by Dr. Starnes.

Hope this helps.