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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).

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 origin. 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.^[1] The PNR is, for nonstop flights, actually beyond the halfway (more exactly, the "equitime") point, since airplanes carry spare fuel, and since later in a flight the aircraft carries less fuel. 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.

Another aviation use is the point during the takeoff roll when there is no longer enough runway ahead of the airplane to safely stop; at this point, the aircraft is committed to taking off.

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.

There are a number of phrases that bear a similar or related meaning:

• Crossing the Rubicon is a metaphor for deliberately proceeding past a point of no return. The phrase originates with Julius Caesar's invasion of Ancient Rome when, on January 10, 49 BC, he led his army across the Rubicon River in violation of law, hence making conflict inevitable. Therefore the term "the Rubicon" is used as a synonym to the "point of no return".
• Alea iacta est ("The die is cast"), which refers to the aforementioned crossing of the Rubicon.
• Burning bridges. The expression is derived from the ancient military tactics that if one were to burn down a bridge after crossing it, one could not cross the bridge back to retreat.
• Burning boats, a variation of burning one's bridges. The Moor commander Tariq bin Ziyad, upon setting foot on the Iberian Peninsula in 711, ordered his ships to be burnt, so that his men had no choice but to thrust forward and fight against their enemy.
• "Break the woks and sink the boats (破釜沉舟)", an ancient Chinese saying referring to Xiang Yu's order at the Battle of Julu; by fording a river and destroying all means of re-crossing it, he committed his army to a struggle to the end with the Qin and eventually achieved victory.
• Fait accompli ("accomplished deed", from the verb "faire", to do), a term of French origin denoting an irreversible deed.

1. ^ The OED places its first printed use in this context to 1941, in an article in the Journal of the Royal Aeronautical Society, which notes that: "Laymen are inevitably intrigued by this fatalistic expression. As a matter of fact it is merely a designation of that limit-point, before which any engine failure requires an immediate turn around and return to the point of departure, and beyond which such return is no longer practical." Other examples given from the 1940s explicitly reference air travel as the origin. No examples in JSTOR date earlier than the late 1930s.

Point of Know Return - The 1977 album by the progressive rock band Kansas

Past the Point of No Return- Phantom of the Opera by Andrew Lloyd Webber

• Calculate and visualize point of no return (radius of action) - as related to air navigation

In the 2001 third person shooter game Max Payne, the character can be heard saying "I was so past the point of no return, I couldn't even remember what it looked like when I passed it."

• Catastrophe theory
• Event horizon
• Jumping the shark
• Milgram experiment
• Sunk cost fallacy