Aviation is becoming more and more reliant on information held in electronic databases for flight planning and for en route navigation use whilst airborne. Twenty or more years ago, aircraft were flight-planned along canned routes developed by specialist navigation departments with information derived from charts, flight guides and from the source Aeronautical Information Publications, the AIPS, themselves. The data was then output in the form of a paper flight plan. The move toward computerization occurred in the mid 1970s and the early systems relied on the construction of waypoint to waypoint routes. Today, aircraft are planned to fly on canned or random routes based on airway to airway segments dependent on characteristics derived from an aeronautical database. Though correlation with paper data exists, the industry has moved a significant way along the path to database dependence for ground-based flight planning. Moreover, the move towards reliance is not limited to the ground alone for, in the case of British Airways at least, all aircraft are equipped with some form of electronic navigation database. Few airlines, if any, with the notable exception of Swissair, have invested in the creation of a comprehensive global navigation database. The costs of creating, maintaining and verifying such a product are more than even large and relatively successful airlines are willing to pay. Instead, they buy in the required ground and air systems products from Jeppesen, Swissair, Racal and the rest. They procure a service secure in the knowledge that the data has been collated, verified and authenticated before publication and use. However, is this reliance misplaced perhaps?

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.