To perform a 360-degree loop, an aircraft needs to achieve three phases in quick succession: the entry, the climb and the exit.
Each of these would cause particular problems to anything the size and weight of even a small commercial jet. Entry has to be undertaken at top speed to carry the plane through vertical ascent, making optimum fuel load a tricky calculation.
At this velocity, the climb would put massive strain on the wings and tail – enough to tear them from the fuselage. Finally, the jet’s weight would be too great and flight controls too weak to pull out of the loop without causing vibrations that could rip the aircraft apart.
Needless to say, nobody has found a pilot brave enough (or airline dumb enough) to try it.
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