Wiktionary
zero-zero
a. Pertaining to the ejection of the occupant of an aircraft from a grounded stationary position (i.e. zero altitude and zero airspeed).
Usage examples of "zero-zero".
After her last zero-zero leap, Envoy paused a while, some seven astronomical units from her goal.
It concerns the possibility that a zero-zero drive, borrowing substrate energy, may kick the universe out of its metastable state and set off an expanding sphere of annihilation.
The zero-zero tail number designated it as the CAG's aircraft, and it was usually kept in top shape.