Maximum Diversion Time/Distance (Etops)

Maximum Diversion Time
The required operational approval by the authority may be granted for different maximum diversion times (rule time), e.g. 120 or 180 MIN, depending on the engine-aircraft combination. As maximum diversion time is based on still air distance, actual diversion time calculated on Operational Flight Plan might be greater.

Maximum Diversion Distance
Is the distance covered in still air and standard conditions based on the One Engine Inoperative (cruise) speed in the maximum diversion time.

Source: ICAO Annex 6