Lightning Current Levels in Aircraft Fuel System Plumbing

Lightning currents passing through fuel system tubing and other conductors in fuel tanks have long been recognized as potential fuel vapor ignition sources. Tests have been conducted on joints, interfaces, and flexible couplers to verify their ability to conduct lightning currents without creating ignition hazards. Prior to the work reported here, there has been very little data upon which to select representative current and voltage levels for these tests.

Using the worst case data (amplitudes and durations) obtained from tests on a Bombardier Dash 8 Q100 representative wing box fuel system, test levels for internal plumbing components were proposed. Using a 6 dB margin on amplitude and a 6 dB margin on duration (2 to 3 times the measured amplitudes and durations for a 12 dB margin overall), the following test levels and waveforms were suggested for testing fuel system components used in this type of medium-sized commuter aircraft:

• fuel system components exposed to Zone 3 currents would be subjected to Waveform (WF) 5B currents (as defined in SAE ARP5412) at 375 A
• fuel system components exposed to Zone 2A currents (through a connection to surfaces subject to direct strike attachment) would be subjected to WF 5B currents of 1,100 A
• fuel system components designed to prevent induced currents would be subjected to WF 4 voltages of 300 V