Unexpected failures modes, or how aeroplanes can bite in very mysterious ways.

Aircraft have certain unique characteristics. In flight they are self contained systems, where at a first approximation everything on the aircraft is capable of affecting everything else. They are also, even at their simplest, complex machines designed to meet conflicting requirements of strength, weight, and controllability. Microlight aeroplanes, whilst amongst the simpler aeroplanes, also often use a wider range of technologies and materials, which combined with a relatively light-touch certification regime, leading to some characteristics that don’t lend themselves to easy analysis, and don’t emerge until aircraft have been in service for some time. Helpfully for the researcher, often their details are available and less sensitive.

This paper will describe some selected examples from the history of British microlighting, and the lessons from them. A Rogallo winged microlight aeroplane where the colour of the wing determined the flying characteristics. A tandem seated aeroplane where not enough friction in a Bowden cable, combined with a slightly larger engine, led to a pitching oscillation of the whole aeroplane that could have led to an in-flight breakup. A state of the art carbon fibre high performance aeroplane which could lose control in certain manoeuvers - a problem solved by introduction of a small shape change to tiny part of the wing. Most recently, a fatal accident was caused by a bend in a small locking pin, and a pilot failing to correctly use a safety device: making the really valuable point that the highly complex system that is an aeroplane, also includes one or more human beings, and their actions (or inactions) will always be an important factor in whether these failures lead to incidents or accidents.