Bob sees a gremlin on the wing of the plane and decides the only possible solution to the problem is to steal the air marshal's gun, open the emergency exit, and shoot the thing.
When a craft project landed them in Europe and love was on the wing, maybe it was time to increase their commitment, smooth out the edges, get a good grip and take flight to keep their hearts aloft.
But if you take more and more rivets and if you take out that key one that's actually holding on the wings of the prop, then the system will collapse. We don't want to get to that point.