As we know, it's not just pilots who can spot something wrong as they look out of the window.
In the 1960s de Havilland, Hatfield, Chief Designer Phil Smith was travelling in a TCA Vanguard and saw that the wing or flap (can't recall which) was not as it should be. There followed a dialogue that was straight out of "No Highway" as he tried to convince the steward that it was important and that he was someone who knew - not helped by his relatively common name.