Ignition Source Current Thresholds in Cracked Fuel Tank Tubing

This paper describes lightning fuel ignition source test data on cracked aluminum and hydraulic tubes. The tube test articles included several different types of cracks and establish ignition source threshold current densities that exceed what is expected in traditional aluminum fuel tanks for midsize business jets, which notably are higher than typical current densities in larger Part 25 airplanes. Additionally, the fuel tube test data compared to ignition source current thresholds associated with tube couplers and fittings show consideration of cracks in the tubing will not typically be a critical factor in showing compliance or determining design constraints.