The constraints imposed by the regulatory authorities give flight crews more tasks to perform at the flight planning stage for an Extended Range Twin Operations (ETOPS) flight than for a non–ETOPS flight. Among the additional checks the flight crew has to make are the following:

(i) That the aircraft will at all times be within the distance, calculated using the still–air single engine speed for the certified time, from the nearest ‘ suitable ’ airfield.(ii) That the ETOPS planning minima, which are typically three times the Category 1 operating minima in terms of forecast cloud base and visibility, are attained for each of the ‘suitable’ airfields used.

(iii) That the weather at each of the ‘ suitable’ airfields used is forecast to be above the planning minima, not just for the time of passing, but for a period, termed the time window, from one hour before to one hour after the expected time of arrival of the aircraft at this airfield.

(iv) That there is sufficient fuel, using the most critical fuel scenario, to take the aircraft from the critical point to any ‘ suitable’ airfield used in the calculation of the route.