A: The incident you are referring to is Tex Johnston's roll of the prototype Boeing 707 at Seafair in Seattle. Yes, it is possible, but that is the only time I know of it being done.

A: Yes, very early in the Boeing 707’s development, pilot Tex Johnson rolled the demonstration airplane over the Seattle Seafair. While physics may permit such a maneuver, good judgment would not.

On Friday, May 14, 1954, just after 4 p.m., the “Model 707” prototype – also known as the “Dash 80” – debuted at the Boeing factory in Renton on the shores of Lake Washington.

The first production Boeing 707, a 707-120 destined for Pan Am, made its first flight on Dec. 15, ... its pilots famously threw thehuge Dash 80 into a barrel roll in front of many industry witnesses.