Vertical perspective 

At first glance, flying is straightforward. First there is a climb phase after the take-off, second the aircraft is cruising on the route and flight level chosen, and third it descends to the destination airport. But these procedures become more complex in busy airspace. Vertical flight paths may cross horizontal ones and vice versa; aircraft need to be sequenced before landing adding complexity to arrival and departure routes; and runway capacity may limit access to the airport at any one moment in time. 

FABEC air navigation service providers are developing procedures and technologies to streamline these processes, including offering smart vertical flight paths to reduce the environmental impact of an individual aircraft in terms of fuel burn as much as possible.