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Flight Phase 2: Departure and Climb
The aircraft will become airborne and commence climbing under direction from air traffic control who allow it to achieve its desired track and climb to cruise altitude while managing its safe separation from other aircraft in the vicinity and allowing for local restrictions such as terrain, weather, noise abatement, etc.
What used to happen?
Traditionally, departures have involved a degree of radar vectoring by air traffic controllers focused on separating aircraft based upon strictly specified vertical and horizontal separation standards. Standard Instrument Departures were primarily designed to maintain the maximum safe utilisation of the airport runway, while maintaining safe separations between arriving and departing aircraft and terrain, and meet noise environmental requirements. Little account was made for optimising departure clearances to achieve optimised departure routes which allowed aircraft to climb and achieve its cruise altitude as quickly and efficiently as possible.
What are we doing today?
Aircraft departure procedures have developed to a point where air traffic control is now able to provide a degree of predictability to the pilots and to allow for unimpeded climbs through to cruise altitude. Air traffic control is also more strategic than it used to be, so that the requirement for air traffic controllers to make short term 'tactical' vectoring decisions is reduced, and procedures have now developed to the point where the airspace around the airport is strategically designed for the most effective use of capacity, air traffic flow and meet terrain and noise requirements, which has also enhanced safety risk management.
Aspire 1 will be provided a priority departure route and unimpeded climb through to cruise altitude, to allow it to reach its optimum cruise altitude as quickly and efficiently as possible.
After takeoff and depending on the community noise requirement, at a height of between 800ft and 3000ft above the runway the engine power will be further reduced to 'Climb Power', the rate of climb reduced and the aircraft accelerated to enable the retraction of the flaps. For fuel conservation it is desirable to reduce power and retract flaps as early as possible. For tonight’s AKL-SFO flight the engine power will be reduced and the flap retraction commenced at 1000ft.
The most fuel efficient departure is one where the aircraft flies the least track miles over the ground and is permitted an unrestricted climb. Too often today aircraft are required to fly on a track in the opposite direction to the destination for several miles before turning towards the destination. ATC may will also hold the aircraft at a fixed altitude to ensure appropriate separation with an arriving aircraft. Performance Based Navigation (PBN) is a concept which takes full advantage of the navigation capabilities and accuracy of modern aircraft systems. The implementation of Performance Based Navigation in the design of departure procedures provides opportunities to significantly improve departure procedures and provide ATC with separation assurance through design so that unrestricted climbs are more likely.
In the climb after take off, there are a number of conflicting factors that an airline must balance to arrive at an ‘optimum’ operating procedure. In terms of the climb power, the use of a ‘Derate Climb Power’ - a power setting up to 20% below the Maximum Climb Power - significantly improves engine life and maintenance costs, but increases the overall fuel consumed during this phase of flight. Even with today’s high fuel prices, the savings to an airline in engine maintenance still exceed the cost of fuel that could be saved in this phase of flight by a factor of over two. Climb speeds are set using a Cost Index entered into the aircraft Flight Management Computer. The theory of Cost Index is covered under the cruise section of this briefing.
Why are we doing it?
The sooner an aircraft is able to track onto its ideal or 'optimised' route following completion of the take off procedure, the less emissions produced. Airways New Zealand has developed departure routes from Auckland airport which take full advantage of the flight's preferred track direction and altitude climb, allowing it to commence it's 'preferred route' to its destination right from the moment of take off.
Consistency and predictability of air traffic control directions for departure and climb are also vital if a pilot is to fly the aircraft in the most efficient and emissions-optimised manner possible. This means an aircraft can smoothly and evenly gain altitude up to its optimum enroute cruise altitude and speed to achieve its most efficient flight profile as quickly as possible, without the requirement to hold at various levels and climb in 'steps', which is less emissions efficient. The departure for the flight tonight will use the minimum track miles and a climb that is only restricted to be consistent with the community noise restrictions that apply at Auckland. For tonight’s flight we have chosen to minimise the emissions and use Maximum Climb Power for the climb.
What does this mean in terms of the bigger picture?
Air traffic control is required to juggle a number of variables in assisting an aircraft achieve its desired route direction right from the runway. Those variables may include the number of other aircraft in the vicinity and how complicated that traffic mix is, through to the type of terrain surrounding the airport and noise abatement areas. Instead of using radar to separate arrivals and departures, airspace procedure design has developed to the point where more precision is now provided to the pilots through procedures designed to provide optimum departure routes and to allow them to safely transit the busy airspace around the airport in the most efficient way possible.
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