Figure 2. Current Path and Sparking in Typical Fastener during Lightning Discharge Figure 1. Cross Section of Typical Fastener

! ABSTRACT —;> Lightning protection of modern aerospace vehicles must prohibit sparking in critical fuel vapor areas. In the past, it has been particularly difficult to keep mechanical fasteners from sparking during a lightning event. Attempts to seal off the fasteners from the critical fuel vapor area by manual application of sealant material have proven to be ineffective due to gaps and voids produced by the application process. A technique was developed by Douglas Aircraft Company to control the application of dielectric sealant material to isolate the mechanical fastener sparking from the critical fuel vapor area. The technique consists of a specially designed dielectric cap that fits over the fastener, providing uniform and controlled application of dielectric filler material. An adequate thickness of filler material provides a ba-rier that prevents the sparks from entering the critical fuel vapor area. The Lightning Spark Barrier is applicable to a wide variety of installations, including those with composite materials. A patent has been applied for.