Failure of electronic equipment represents a significant proportion of the overall defect rate for modern aircraft. While this is not entirely surprising in view of the quantity of electronic equipment installed, and the variety and multiplicity of functions performed, it remains a serious problem.

The specific reliability of electronic equipment, in terms of separate facilities, has tended to show marked and continuous improvement, but this has been overshadowed by the increasing number of functions performed, and by greater dependance on this equipment. Most electronic failures occur without warning, and many of the remainder need delicate and complex test procedures to obtain even a few hours warning of impending failure. In some instances, particularly where electronics is used because of its rapid reaction time, a fault can, unless special precautions are taken, be a serious risk to safety, or cause other serious consequences even before there is any warning that a fault condition exists.