Avgeek Alert: What Is ´Continuous Descent Approach´?


What goes up, must come down, right? Landing is of course a routine part of any flight, but there are ways to do it that are more efficient – and even environmentally sustainable – than others. One example is the maneuver known as continuous descent operations (CDO), also known as continuous descent approach (CDA).  which aided by air space design and air traffic control allows a flight profile which optimises the aircraft´s abilities and benefits airport transit.

This maneuver involves low-engine-thrust- (plus, whenever possible, also a low-forward-resistance) configuration. To put it simply, a descent profile with a standard angle is adopted and a continuous downward trajectory is initiated, as if the aircraft were sliding down a slide. This is as opposed to conventional descent, in which the plane approaches the runway as if tracing the profile of a staircase (descends at an angle one section, advances another horizontally and so on until landing). The angle of the descent path will vary depending on the type of aircraft, but also weight, temperature, atmospheric pressure and many other variable factors. Normally, this maneuver can be predefined with or without the help of the air data computer/flight management system.

The Goals of CDOs/CDA

According to the International Civil Aviation Organisation (ICAO), they are:

  • To achieve greater operational security within the airport.
  • To increase the capacity of those same spaces.
  • To boost aircraft efficiency.
  • To protect the environment.

Some Advantages of CDOs/CDA

  • Increases operational security.
  • Improves airspace efficiency.
  • Enhances the predictability (and therefore the safety/security) of flights.
  • Decreases fuel consumption (and therefore emissions/carbon footprint).
  • Reduces pilot and air-traffic-controller workloads.
  • Lessens the impact of noise on towns and areas near the airfields.

Types of CDO/CDA Operations

There are basically two. One is the “open trajectory”, in which the operation ends before the final approach stage and which permits greater flexibility. The other is “closed trajectory”, in which the lateral light path is predefined right up to and including the final approach stage; the advantage is that it improves the predictability of flights; lessens their acoustical impact on surrounding areas (by more than 40 percent);  and boost their efficiency, with remarkable fuel savings and a reduction in pilot/air traffic workload and the need for them to communicate between them as much.

When CDOs/CDA Are and Aren´t Possible

Continuous descent operations have been restricted at some airports – where they simply aren´t efficient or even feasible. But other airports allow a higher percentage with the idea that these are sustainable and allow for greater operational fluidity, and here they must take into account both the arrival rate as well as other aircraft which come and go without making a CDO and others which merely overfly the space. The ICAO recommends a step-by-step implementation, including a prior evaluation of operational safety.

Spain Leads Europe

ENAIRE, the government body which oversees air navigation in Spain, began including continuous descent operations years ago, and its Flight Plan 2025 includes an environmental sustainability strategy in which this type of maneuver plays a role, especially during nighttime operations, when the acoustical impact is less. ENAIRE data indicate that ours is the country that leads this type of maneuver, with a percentage much higher than the European average; in the first half of 2022, for example, Spanish controllers authorised an average of 36 percent of CDOs/CDA, compared to 15 percent that the continent offers on average. That year, the airport with the highest percentage of Europe´s major airports was Málaga-Costa del Sol (AGP), where continuous descent operations were authorised were 47 percent, with Gran Canaria coming in second at 43 percent, followed by Palma de Mallorca (38 percent), Barcelona El Prat (36 percent), and Madrid Barajas (28 percent). All told, these five Spanish airports are among the top eight in Europe.


Photo | Mateusz Atroszko