Software on the edge

As our society becomes more technologically complex, computers (and the software that they run) are being used in a potentially alarming number of high consequence safety-critical applications. When these systems fail, the outcome can be devastating. For example, several years ago a British Midland 737 aircraft crashed killing 47 people and seriously injuring 74 others. The reason for the crash was due to a failure in the engine control system. The control system monitors the engines of the aircraft and if the vibration of an engine falls in a particular range, the engine is deemed faulty and is shut down. Unfortunately, on this particular flight the vibration of a faulty engine exceeded the range checked for in the control system. Thus the corresponding sensor sensed a value that was not a “believable value”, and therefore the faulty engine was not shut down. To make matters worse, the vibration of the faulty engine traveled through the frame of the aircraft and was picked up by the vibration sensor of the functioning engine. This second vibration sensor concluded that the functioning engine was faulty and shut the engine down-resulting in the crash. A post mortuum analysis determined the probable cause of the crash to be “inadequate parameterization of the software-based control system [4]“. Because of failures such as the one described above, many people believe that “the software industry remains years behind, perhaps decades short of the mature engineering discipline needed to meet the demands of an information-age society[2]“. In spite of this, our society’s dependence on software has been growing dramatically. “The amount of code in most consumer products is doubling every two years...televisions may contain up to 500 kilobytes of software; an electric shaver, two kilobytes, the power trains in new General Motors cars run 30,000 lines of computer code[2]“.