The point of no return is the point beyond which someone, or some group of people, must continue on their current course of action, either because turning back is physically impossible, or because to do so would be prohibitively expensive or dangerous. It is also used when the distance or effort required to get back would be greater than the remainder of the journey or task as yet undertaken.
A particular irreversible action (e.g., setting off an explosion or signing a contract) can be a point of no return, but the point of no return can also be a calculated point during a continuous action (such as in aviation).
Origins and spread of the expression
The term PNR—"point of no return," more often referred to by pilots as the "Radius of Action formula"—originated, according to the Oxford English Dictionary, as a technical term in air navigation to refer to the point on a flight at which, due to fuel consumption, a plane is no longer capable of returning to its airfield of original takeoff. After passing the point of no return, the plane has no option but to continue to some other destination. In this sense, the phrase implies an irrevocable commitment.
For nonstop flights between two definite locations, the PNR is actually beyond the halfway (more exactly, the "equitime") point, since aircraft usually carry more fuel than is necessary to reach the destination. For example, on a 2000-mile flight, should the tanks have enough fuel for a 3000-mile flight, the halfway point would be at 1000 miles, but the PNR would be at more than 1500 miles.
Neither does the PNR correspond to the halfway point of fuel usage. With loss of mass due to fuel consumption, it takes less fuel for an aircraft to cover a given mileage. An aircraft might expend, say, 60% of its total fuel load before reaching the PNR. The PNR can be further extended in this manner by dropping unnecessary fuel tanks or ordnance.
Another aviation use is the point during the takeoff roll when there is no longer enough runway ahead of the airplane to stop safely; at this point, the aircraft is committed to taking off. (See also V1 speed.) In mountain aviation, the phrase is sometimes used in a completely different way to refer to the point at which the grade of the terrain "outclimbs" the aircraft—that is, the point at which a crash is inevitable, being a parallel in common usage. The phrase can also be used in this sense to denote inevitable disaster.
The first major metaphorical use of the term in popular culture was John P. Marquand's novel "Point of No Return" (partially serialized in 1947, published in book form in 1949). It inspired a 1951 Broadway play of the same name by Paul Osborn. The novel and play concerned a pivotal moment in the life of an American banker, but they also explicitly referenced how the original expression was used in World War II aviation.
Since then, "point of no return" has become an everyday expression, with its aviation origins probably unknown to most speakers. It has served as a title for numerous literary and entertainment works.
There are a number of phrases with similar or related meaning:
- Beyond a certain point there is no return. This point has to be reached. is a quote from Franz Kafka's Aphorisms (Betrachtungen über Sünde, Leid, Hoffnung und den wahren Weg - 1918)
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