# Optimising Continuous Descent Approaches (CDA): Seeking Strategies and Rules of Thumb

Ideally, approaches should be executed as a continuous descent approach (CDA), maintaining idle thrust and only levelling off (or reducing vertical speed to <500 fpm) briefly to reduce speed, while still keeping the thrust at idle.

While I cannot speak for every region, in Europe, executing a CDA is widely regarded as the most beneficial method of flying. It conserves fuel, as engines are at idle, and significantly reduces noise pollution. The majority of European airports support CDAs, although there are exceptions. For instance, Bergerac Airport in France necessitates maintaining an altitude of 2,500 feet for an approach to runway 27.

As a Boeing 737 pilot, I am keen to learn about any rules of thumb or strategies that other pilots employ to effectively execute a Continuous Descent Approach (CDA), particularly when piloting a Boeing 737. I aim to stay in VNAV, but I am also prepared to utilise LVL CHG and V/S as required. Our company's Standard Operating Procedures recommend using a 10nm ring for the landing runway, and I make use of the altitude range arc (known as the “green banana”) to enhance situational awareness.

Let’s take London Gatwick as an example:

In my flight planning I may work out what maximum altitude I need to be at 10nm out using this calculation:

Altitude at 10nm = Altitude at 5nm + 5 x (altitude loss per nm on glideslope)
= 1840 + 5(1840-1520)
= 3440 ft


The chart gives the 5.5nm to intersect the glideslope at 2000', but I may also write down what altitude I would intersect the glideslope at 3000':

At 3000’, mileage required = (3000 - Aerodrome Elevation)/(altitude loss per nm on glideslope)
= (3000-203)/(1840-1520)
= 8.7nm


I would write these 3 altitude-distances down and refer back to them during the descent to make sure I am on profile. I would cross reference my progress with the "green banana" and 10nm range ring, and of course the VNAV profile (737 specific).

What effective rules of thumb or strategies can be employed to effectively execute a CDA?

• When considering altitude at specific distances, such as 10nm out, do you rely on pre-calculated altitude-distances, or do you employ a more efficient, quicker mantra?
• Are there any more reliable or simpler techniques to enhance situational awareness during a CDA, ensuring adherence to the desired glide path without deviating too high or low?
• In scenarios such as encountering a stronger than anticipated tailwind, how do you adjust or preemptively manage being high on the approach? What indicators are you looking for to inform you that you are high on approach.

Personally, I find that the most critical point is from ~7000' to ~4000', trying to balance the best moment to decelerate and/or keep on the profile.

• When I was on a team that developed (what we called) Continuous Descent Arrivals in the US the team was also comprised of representative pilots from the major air carriers servicing that airport. As I recall, the FMS flew the arrival/approach automatically. Does your aircraft not do this? Commented Apr 13 at 2:29
• @RetiredATC I’m not sure what it is like in States, but in Europe we rarely follow the actual STAR arrival. By radar vectoring, we will often expect (quite dramatic) shortcuts on the STAR or a vector to a 10nm final etc. So we find that we can’t accurately predict and therefore can’t program the true arrival in then FMS. Even if you fly on the arrival track exactly, a tailwind may get you high on profile (quite insidiously). So we can rely on the FMS to a certain extent, but situational awareness of vertical position is also incredibly important. Commented Apr 13 at 7:11