point of no return

The expression originated in air navigation planning. The point along the planned flight path beyond which an aircraft will no longer be capable of returning to the takeoff airfield or an alternate airfield due to insufficient fuel is calculated before takeoff. This is mandatory for overwater flights or flights without alternates on route.

point of no return (plural points of no return)

1. (aviation) The point in an aircraft's flight when there is insufficient fuel to reverse direction and return to the place of origin.
2. (figurative) The point in any process or sequence of events where some development becomes inevitable.
   • 1959, Roger Burlingame, I Have Known Many Worlds, page 216:

     After Munich it became daily more evident that Hitler had passed the point of no return. With every burst of news from Europe the inevitability of war became more certain.

   • 1964 May, “News and Comment: Liner trains and the NUR”, in Modern Railways, page 290:

     [...] this trickle of loss going on relentlessly week by week will gradually reduce miscellaneous merchandise loadings on the railways to a point of no return, where the entire business must be abandoned to cut steeply mounting losses.

   • 1999, Malcolm Ludvigsen, General Relativity: A Geometric Approach, page 152:

     However, for slightly larger stars, no such final equilibrium state is possible, and in such a case the star will contract beyond a certain critical point — the point of no return — where complete gravitational collapse leading to a spacetime singularity is inevitable.

   • 2005 September 16, Steve Connor, “Global warming 'past the point of no return”, in The Independent‎, archived from the original on 2007-01-15:

     A record loss of sea ice in the Arctic this summer has convinced scientists that the northern hemisphere may have crossed a critical threshold beyond which the climate may never recover.

Because of undesirable connotations elicited by the figurative use of the term, its use in air navigation has been superseded by the term point of safe return (PSR).

• PNR, PONR
• rubicon
• threshold

• equitime
• inevitability
• the die is cast

• point of no return on Wikipedia.Wikipedia
• “the point of no return”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022.