point of no return
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point of no return[′pȯint əv ¦nō ri′tərn]
A point along an aircraft track beyond which the aircraft's fuel supply will not permit it to return to its own or some other associated base but must continue in attempt to reach its destination.
point of no return (PNR)
critical point unless the minimum reserve of fuel is carried. While there are many formulas for calculating PNR, the illustration indicates one in the simplest case, when an aircraft is flying from A to B in a straight line. See also critical point.