SAE ARP5412 is the SAE Aerospace Recommended Practice that defines the lightning environment an aircraft may encounter and the waveforms by which that environment is represented in design and test. It is a definition document rather than a test procedure: it answers the question of what the aircraft must be protected against, leaving the question of how the protection is verified to its companion. The document describes the composition of a lightning strike in terms of the current components that a strike delivers, distinguishing the initial high amplitude component that attaches to the aircraft and may be compared with the whole of a natural flash, the continuing current that flows afterwards and is significant because of the charge it transfers, and the subsequent and restrike components that follow. From those components it derives the standardised waveforms, their amplitudes, durations and transfer of charge, and it identifies which of them apply to the various parts of the aircraft, from the nose and wing tips where attachment is likely to the trailing edge and the tail where the current leaves.