A Realistic Approach to Aircraft Lightning Protection

Lightning protection for fighter aircraft is presently based on the requirements of MIL-B-5087 and refined by the recently issued MIL-STD-1757. These documents specify current and energy levels sufficient to cover greater than 99 percent of the cloud-to-ground strikes. These levels are applied to aircraft according to lightning strike zones established by attach point analysis and test. The application of these specifications to aircraft is made without consideration of mission, probability of strike occurrence, or penalties associated with protective designs. Data from recent in-flight test programs, a tabulation of aircraft strike rate per aircraft type, and an examination of strike damage records, all show that the requirements may be too stringent and that a revision to the method of applying lightning specifications to aircraft may be justified. In conventional and VSTOL high-technology fighter aircraft, weight has a direct effect upon performance, combat effectiveness, losses, and life-cycle cost. Unnecessarily stringent lightning protection requirements can add weight out of proportion to the lightning risk. A systematic method of tailoring requirements to risk or damage probability is desirable to provide a more balanced protective design. This paper presents a probabilistic approach to the design of aircraft lightning protection which may be a useful method of avoiding conventional worst case design penalties.