“... an iron curtain has descended across the Continent.” — Sir Winston Churchill (1946)
22.6.6 Breaking Off
A player may, after any round of Long-Range or Stand-off combat, voluntarily Abort an aircraft unit. Simply place the unit in the appropriate Abort Box. Only units which were actually engaged in combat may voluntarily abort.
I would read that to mean there must be some combat during the Long–Range or Stand–off phases (i.e. at least one aircraft has to attack).