One paragraph of this ode to the 747 blew me away: “Even then, and despite the 747’s formidable technical specification, it has always seemed a wonder that such a massive machine can actually get off the ground, let alone fly so fast – the plane cruises at Mach 0.85-0.88, not far below the speed of sound – and so very well. No one knows if a 747 will barrel-roll or loop-the-loop because no pilot has been mad enough to try. Boeing engineers think both manoeuvres might be possible, although 400 passengers tucking in to chicken-or-fish and red-or-white wine might never forgive a pilot willing to have a go.”
A barrel-roll? WTF? Anyway, I poked around a bit more and it sounds like it’d be possible, though as The Straight Dope points out, “The problem is not so much with the strength of the wings, which are designed to stand much greater pressures, as with the skill of the pilot.” Oh, and some guy actually rolled a 707 in a display flight.