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For conventional metallic aircraft lightning protection methodologies have generally been well established by years of flight experience. However, recent events have highlighted the need to take into account the effects of age or existing fault conditions. For lightning this could mean currents being conducted across unbonded couplings, across bond straps which make intermittent contact, or by debris or chafed wires bridging to fuel gauges and their wiring. The paper discusses the effects of transient currents flowing through intermittent contacts, and the levels at which such transients present a potential threat for fuel ignition. In the main this is a review of existing data, but supported by experimental studies which are just beginning at Culham. The work has been carried out under the European EM-Haz and the Culham Lightning Club programmes

In the EU FULMEN collaborative project a series of experiments based on AEA Technology’s Hawker Hunter airframe have studied coupling of E and dE/dt threats. Currents and fields were applied using either a low level lightning current simulator to the whole airframe, or by injecting the threats more locally. Coupling could be measured in two apertures at opposite ends of the airframe, in which cables were routed both parallel and perpendicular to the current paths. The different configurations for measurement and test allowed the various coupling methods to be separately elucidated. Likely levels of E-field and d2B/dt2 coupled transients which could couple to internal equipment are discussed in relation to the present consensus of external environments.