At this summer's Farnborough Air Show in England, the talk was dominated by the mishaps of one plane: the Lockheed Martin F-35 Lightning II, also known as the Joint Strike Fighter. Due to be adopted by major air forces in the decades to come, it was supposed to be the star of the show. But in the end, the $100m-a-unit jet failed to turn up to its coming-out party after an engine fire in one of the production models grounded the fleet.