A simple formula is presented for the safe life of an aircraft under reasonably good operating conditions from the standpoint of wing fatigue. Gusts are treated as the main factor in determination of fatigue life, though other factors are allowed for as being secondary. Before the formula can be used a simple fatigue test is required on critical components, and is repeated several times to establish variation of nominally identical specimens. The loading cycle for this test corresponds to a sequence of up and down gusts of 8 ft./sec. equivalent velocity. The life obtained is termed the “Standard Life” and corresponds to normal operating conditions on European air lines. Reservations in the use of the formula and correction for other operating conditions are discussed in general terms.