Computer software in civil aircraft

Abstract

Airborne software is an increasingly large and important system element. However, it is only one element of aircraft systems, and only one element of the aviation software environment. Consequently, it must be considered similarly to the other system and software elements, and cannot be considered in isolation. It is commonly appreciated that there are no such things as systems that are free from risk, but only systems that reduce overall risk and improve overall performance. The apportionment of risk varies with the systems, some of which contain software. Airborne software, like other system changes, is used where its benefits outweigh its disadvantages, notably to improve human factors, which are involved in most aircraft accidents. The timescales involved extend over many decades, and involve a large number of suppliers. Airborne software is produced in accordance with uniquely severe aviation standards, and has now been in service for over 20 years. Other safety critical industries are only now beginning to put into service software with comparable standards. These standards ensure that very great efforts are made to aim at freedom from errors, but freedom from faults is not assumed, and thus fault consequences are assessed and dealt with on a continuing basis, as is the practice in other aspects of aviation systems. A number of powerful tools have been developed to facilitate software development and compliance with these standards. The service record of aircraft that incorporate airborne software has shown that the promise of benefits has been realized. For decades airborne software has been contributing, and continues to contribute, towards making aviation more efficient, and above all, safer.