Continuous Climb & Descent Operations



1.0 INTRODUCTION


1.1 Traditionally, Air Traffic Control manages departures and arrivals by providing clearances to a series of higher or lower altitudes. These incremental altitudes are determined tactically by the ATCO based on traffic, route and airspace. In the climb and descent phase of flight an optimum flight path should be flown according to the pilot’s needs, typically for fuel efficiency. These flight paths are considered “continuous” because there is typically no level-off. Achieving continuous climbs and descents is a goal of our ATC


1.2 IFATCA defines Continuous Climb Operations as: Continuous Climb Operations (CCO) are aircraft operating techniques facilitated by appropriate airspace and procedure design which meet all ATM requirements, allowing the execution of an optimized climb profile.


1.3 IFATCA defines Continuous Descent Operations as: Continuous Descent Operations (CDO) are aircraft operating techniques facilitated by appropriate airspace and procedure design which meet all ATM requirements, allowing the execution of an optimized descent profile.



2.0 DISCUSSION


2.1 Continuous Climb Operations (CCO) - is an aircraft operating technique made possible by appropriate airspace and instrument procedure design and appropriate ATC clearances enabling the execution of an optimized flight profile to the performance of the aircraft, thereby reducing total fuel burn and emissions during the entire flight.

The climb is the phase of operations that uses the highest rate of fuel during a flight. An aircraft’s fuel efficiency in terms of fuel burned per kilometre flown in level flight increases with height. However, the fuel used in climbing to that altitude can be a significant part of the overall fuel used for the flight. The optimum vertical profile takes the form of a continuously climbing path. Step climbing of an aircraft should be avoided as far as practical.


2.2 Continuous Descent Operations (CDO) - is an aircraft operating technique aided by appropriate airspace and procedure design and appropriate ATC clearances enabling the execution of an optimized flight profile to the operating capability of the aircraft, with low engine thrust settings and, where possible, a low drag configuration, thereby reducing fuel burn and emissions during descent. The optimum vertical profile takes the form of a continuously descending path, with a minimum of level flight segments only as needed to decelerate and configure the aircraft or to establish on a landing guidance system (e.g. ILS). Step descending of an aircraft should be avoided as far as practical. The maximum benefit for an individual flight is achieved by keeping the aircraft as high as possible until it reaches the optimum descent point. This is most readily determined by the onboard FMS. Ideally, to maximize the benefit of a CDO it should start at the top of descent and continue through to the final approach fix (FAF) or establishment on the landing guidance system.

Note 1.— An optimum CDO starts from the top of descent and uses descent profiles that reduce segments of level flight, noise, fuel burn, emissions and controller/pilot communications, while increasing predictability to pilots and controllers and flight stability.

Note 2.— A CDO initiated from the highest possible level in the enroute or arrival phases of flight will achieve the maximum reduction in fuel burn, noise and emissions.

“In the most ideal form of [continuous descent], a descending aircraft will not apply any throttle during descent. Instead, the potential and kinetic energy of the descending and decelerating aircraft will be managed optimally. The arriving aircraft will be able to glide down from cruise with its engines set to idle while transferring its kinetic and potential energy into the drag on the airframe. In that case, the fuel burned and pollutants emitted during arrival will be minimized. This is what is generally known as a continuous descent arrival (CDA).” (Shresta et al., 2009) http://atmseminar.org/seminarContent/seminar8/papers/p_132_CDA.pdf


2.3 Facilitating CCO and CDO - Air traffic controllers are required to provide safe and efficient management of departing and arriving aircraft. Such fully optimized flight paths are not always possible due to the traffic flows both into the same airport as well as flows into and out of other airports in the vicinity, for example our TMAs. However, while a fully optimal CCO/CDO may not be possible, a CCO/CDO carried out with the appropriate ATC clearances even over shorter sections of the climb/descent phase, can provide significant benefits.


2.4 Benefits - In improving the continuity of vertical operations the following benefits are expected :-

  1. Reduction in both controller and flight crew workload by reduction of the number of required radio transmissions with less climb and descent clearances with intermediate altitudes.

  2. Environmental benefits through reduced fuel burn and reduced exhaust gases, in particular a reduction in Carbon Dioxide emissions.

  3. Financial savings - fuel economy due to more fuel-efficient aircraft performance with more efficient climb and descent operations.

  4. More consistent flight paths and stabilized approach paths; more efficient use of airspace and route placement



3.0 CONCLUSION


3.1 CCO and CDO operations allow arriving or departing aircraft to descend or climb continuously, to the greatest extent possible. Aircraft applying CCO employ optimum climb engine thrust and climb speeds until reaching their cruising levels. With CDO, aircraft employ minimum engine thrust, ideally from top of descent and in a low drag configuration, prior to the final approach fix. Employment of these techniques reduces intermediate level-offs and results in time being spent at more fuel-efficient higher cruising levels, hence significantly reducing fuel burn and lowering emissions and fuel costs


REFERENCES

  1. ICAO Doc 9993 - Continuous Climb Operations Manual

  2. ICAO Doc 9931 - Continuous Descent Operations Manual


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