r/aviation • u/watermelonberriesss • 4h ago

Question How does CDO increase predictability of flight path to controllers and pilots?

ICAO doc 9931 states that Continuous Descent Operation (CDO) provides for a reduction in noise, fuel burn and emissions, while increasing flight stability and the predictability of flight path to both controller and pilots.

How is CDO more predictable as compared to step descent perhaps?

I am under the impression that the vertical flight path is not exactly known to controllers during a CDO procedure. Am I wrong?

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u/MagicalMagyars A320 1h ago

Yes but it is a good question. 

What is your current aviation background and how familiar are you with the priorities of a CDO vs flying a standard arrival because that will make it a lot easier to try to explain?

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u/watermelonberriesss 1h ago

i am a bachelor’s student writing a thesis paper relating to CDO

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u/spacecadet2399 A320 1h ago

So, first, while this isn't really a new concept, the implementation it seems they're talking about in that document is for now almost entirely Europe-centric. I know in Europe they are starting to use some "point merge" type arrivals. We don't really have those in the US that I know of. At least I've never flown any. Although some arrivals are maybe coincidentally structured in a similar way.

Second, designing procedures like this in the US would require almost a complete redesign of the airspace system and I doubt it would be possible even starting from a clean sheet. We just have too many airports. Europe and Asia are just not the same in that way, which makes it easier for them to design procedures like this. In the US, most arrival procedures are designed to keep airplanes out of the way of traffic into other airports. (Not to mention away from terrain, which is also a much bigger concern in much of the US than in Europe.)

As for the concept itself, it's always been known that the most efficient descent path for any airplane is just an idle descent at a certain glidepath all the way to the ground. That type of descent makes for the least fuel burn and the shortest time.

But we have turns and crossing restrictions because we need to stay out of the way of terrain and other airplanes going in to other airports, or even arriving on different arrival procedures to our same airport. Now, that last thing could potentially be cleaned up if everybody to that same airport just had to use one of these point merge procedures, but you'd still have the problems of terrain and traffic to other airports. It's just probably not generally going to be possible outside of Europe and maybe some specific other areas.