The dependence of minimum‐time routes over the North Atlantic on cruise altitude

Abstract

North Atlantic air traffic is broadly organized into a track system: daily sets of tracks are defined by air traffic control, which are vertically stacked, such that the same set of tracks is used for all flight levels (FLs), regardless of any vertical variations in wind. The present paper uses minimum‐time routes, previously shown to be a good proxy for the location of the North Atlantic track system, to understand whether vertical variations in wind speed and direction significantly affect minimum‐time routes optimized at different altitudes. It does so to examine whether (all other factors assumed equal) there is potential for improvements in fuel efficiency. The optimum cruise altitude over the North Atlantic is determined, focusing on the New York–London route. It is found that eastbound routes, which take advantage of the jet stream, are on average faster at 250 hPa (FL340) than at 300 hPa (FL300) or 200 hPa (FL390) by approximately 2 min (compared with the annual mean route time of about 330 min, assuming a true air speed of 250 m/s). For westbound routes, the route time increases with height: aircraft flying at 300 hPa are on average 3 min faster than at higher levels (the annual mean optimum time being about 400 min). These estimates are compared with the time penalty that arises from flying a route optimized at 250 hPa at the other two altitudes. The time penalty is generally less than 1 min compared with the minimum‐time routes calculated at those altitudes.