Increasingly, UK defence procurement is being carried out as part of internationally collaborative programmes. Purchases may be of off-the-shelf design or of equipment meeting the requirements of more than one country. This paper addresses the issue of differing national standards for safety-critical software and the need for harmonisation. Differing standards give rise to a number of issues peculiar to software. One such issue is that all standards for software make requirements on the process used to develop the software. When an existing design is purchased the software development process has been completed and therefore cannot be modified. The requirements of differing standards for physical properties such as structural strength can be compared either by reference to an appropriate scientific theory or by experiment. Unfortunately, neither of these approaches can he used to compare objectively the requirements of software standards, especially when the software is safety-critical. The paper compares some of the existing standards to safety-critical software in military avionics and, describes developments taking place in different countries. (C) 1997 Elsevier Science B.V.
