deadman’s curve
n.— «In its ruling, the F.A.A. said that, by hovering at low altitudes, “sightseeing helicopters are operating in the avoid area of the height-speed envelope (deadman’s curve).” A helicopter flying too low cannot, in an emergency, use the maneuver known as autorotation to settle gently down.» —“Helicopters Over Hawaii: Dogfight on Safety Rules” by Jack Cushman New York Times Jan. 29, 1995. (source: Double-Tongued Dictionary)
Further reading
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An interesting example of a technical adaptation of a common-language term. Long before there were helicopters (or automobiles), the term was often used to refer to a stretch of railroad with a dangerously sharp curve; one, near Cle Elum, WA, was known as Deadman’s Curve — and a great concern to railroad engineers — as early as 1892. It was finally straightened out only after a fatal wreck 50 years later. Another deadman’s curve was the site of a wreck in a Brooklyn subway that killed 97 prople in 1918. More recently, most deadman’s curves have been on highways, as immortalized (yes, poor choice of words) in the hit single of the same name by Jan and Dean from the early 1960s.