Good formula / rule of thumb for CDA
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ATC will take you down to a certain level, like FL070. Absolutely no planning required.
They will keep you there to a certain point, where they are allowed to let you descend further.
They will keep you there to a certain point, where they are allowed to let you descend further.
Surprisingly many captains from such countries who join us, have no clue on how determine whether they're on profile or not, unless they have the route accurately programmed and then read the VNAV profile. Situational awareness is key when flying.
You always have to be able to see through the clearances and keep a backup calculation on what the ATC tells you to do. Usually as a captain, you're solely responsible for what you do. I've been cleared to fly into mountains and other airplanes' paths by ATC.
What the original poster is asking about, is how to manage his deceleration / configuration - while continuing to go down.
However, if you want to have a continuous descent and reach a point at a certain altitude, configuration and speed without adding more thrust than necessary, well... then you have to do some planning!
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...but it's all irrelevant for the topic!!! Why not start a topic about descend planning if you feel so strong about demonstrating your mighty knowledge.
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Yes your ToD becomes irrelevant, when ATC takes you down 200 nm prior to you destination, gives you 10 step descends and controls your rate in between (all due to airspaces structures).
If you need to start a decent "NOW", use the minimum directed/legal descent rate until you intercept the VNAV profile (which will likely be very close to the traditional 300 ft/NM guideline, should you lose the VNAV profile indicator).
Slowing down on that profile is simple: Use speedbrakes, flaps, and landing gear as necessary to add drag and maintain the profile at the lower speed. Once you're below 10,000' (where the noise nazis reside), you'll be at 250 KIAS max (generally 240 or less), so adding drag should not be a problem.
I definitely cannot understand why you consider all this information "irrelevant"! If you can plan a descent from 100 mi out, why can't you plan one from 10 or 20 miles?!?
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Ok, I'm going to try it different:
If a guy asks:
"How can I best plan a visual approach. Do you have any advise for which heigh and speed I should have a different gates? When should I start to configure?"
Is it then a good and helpful answer to explain how to best plan your TOD descend?
This is exactly the same. CDA, in this (Euro) context, is an extension of the approach. So far none of you gave any useful tips for the original poster about how to go about doing his approach.
On the contrary:
It's not trial and error. There are techniques you can employ. I gave my technique in post 5. I am sure other have different ones.
Flying level is also bad advice, when ATC expects you to do a constant descend for noise abatement. And by the way, nobody is requiring the CDA to be made at idle (though of course it would be optimum). It's not a fuel saving thing, it's noise abatement. Going down with 45% N1 is perfectly acceptable, as it makes less noise than flying level with 65-75%.
What the guy is probably looking for is this:
What rate (in what height, at what distance to FAP, at what speed) should I set to enable a continuous deceleration that will ensure I reach the FAP at the prescribed altitude, at the right speed with approach flaps configured.
Such a formula won't work, as you need a variable rate, to facilitate the slowing down, according to the aerodynamic at 240-250, clean and with the different flap settings, of the plane you fly. Also the ground speed is changing, requiring a different rate to keep the desired path. Idle descend rates also differs according to the speed and configuration changes.
Hence my advice in post 5. Get a good starting position, like 5000 feet AFE at 250 knots, with 20 nm track miles to the runway (it's on the low side and won't get the original poster into trouble). Obviously you get to that point through descend planning (if ATC didn't manage your descend from 200nm out). But this is not the part the poster is asking about.
From said point onwards, it's evaluation of how the slowing down is going during the progression. And reaction to that progression. As described in my post 5.
You want to turn all that into a mental calculation?? What is needed is a good sense of TLAR, that you get from repetition practice. Or you can learn in the beginning by watching and OBSERVING how VNAV is doing it (advice post 4).
You can plan where you want to start out. The rest is reacting to the progression.
You are assuming the original poster is an idiot (thus being disrespectful), and doesn't know how to plan a descend. I am not, as he is actually asking about the part (deceleration), which is actually difficult (especially for someone who might be relatively new in the business) and requires a great deal of anticipation.
----different topic----
"ABC123, keep a rate of 2000 fpm or greater until out of FL250".
P.s.
I do feel that descend planning is important too. It just have no relevance for the topic at hand.
If a guy asks:
"How can I best plan a visual approach. Do you have any advise for which heigh and speed I should have a different gates? When should I start to configure?"
Is it then a good and helpful answer to explain how to best plan your TOD descend?
This is exactly the same. CDA, in this (Euro) context, is an extension of the approach. So far none of you gave any useful tips for the original poster about how to go about doing his approach.
On the contrary:
For slowing down, it's trial and error. It depends alot on the wind and the grossweight with the 737NG but I assume it's the same with the bus. In the beginning, try to slow down in level flight to get to know the energy management of the aircraft, note the distances and times needed, to make some mental rules of thumb and then start combining the slowing down while descending at the same time as you get more confident.
Flying level is also bad advice, when ATC expects you to do a constant descend for noise abatement. And by the way, nobody is requiring the CDA to be made at idle (though of course it would be optimum). It's not a fuel saving thing, it's noise abatement. Going down with 45% N1 is perfectly acceptable, as it makes less noise than flying level with 65-75%.
What the guy is probably looking for is this:
What rate (in what height, at what distance to FAP, at what speed) should I set to enable a continuous deceleration that will ensure I reach the FAP at the prescribed altitude, at the right speed with approach flaps configured.
Such a formula won't work, as you need a variable rate, to facilitate the slowing down, according to the aerodynamic at 240-250, clean and with the different flap settings, of the plane you fly. Also the ground speed is changing, requiring a different rate to keep the desired path. Idle descend rates also differs according to the speed and configuration changes.
Hence my advice in post 5. Get a good starting position, like 5000 feet AFE at 250 knots, with 20 nm track miles to the runway (it's on the low side and won't get the original poster into trouble). Obviously you get to that point through descend planning (if ATC didn't manage your descend from 200nm out). But this is not the part the poster is asking about.
From said point onwards, it's evaluation of how the slowing down is going during the progression. And reaction to that progression. As described in my post 5.
You want to turn all that into a mental calculation?? What is needed is a good sense of TLAR, that you get from repetition practice. Or you can learn in the beginning by watching and OBSERVING how VNAV is doing it (advice post 4).
You can plan where you want to start out. The rest is reacting to the progression.
You are assuming the original poster is an idiot (thus being disrespectful), and doesn't know how to plan a descend. I am not, as he is actually asking about the part (deceleration), which is actually difficult (especially for someone who might be relatively new in the business) and requires a great deal of anticipation.
----different topic----
If you need to start a decent "NOW", use the minimum directed/legal descent rate until you intercept the VNAV profile (which will likely be very close to the traditional 300 ft/NM guideline, should you lose the VNAV profile indicator).
P.s.
I do feel that descend planning is important too. It just have no relevance for the topic at hand.
Last edited by cosmo kramer; 10th Jul 2015 at 09:51.
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You take great pride in your post #5, which also gives no "useful tips" by your own [implied] definition. How is
any more useful than the
that you declare as "contrary" to useful?
You also give an example, but so did others...
To an extent, for the person who asked the question, it IS "trial and error"! Since he apparently does not yet have a good feel for his airplane, the best he can do is meld his FCOM procedures with any or any mix of the examples, techniques, and guidelines given here. If he is unable to start at 20 NM and 5000' (your single example), he will have to interpolate, find another guideline, and/or calculate a path using his own devices.
Getting TO a standard (or or reasonably close) profile in the "Euro" environment you describe is likely harder than staying on it. However, if you "know" that your initial VNAV rate of descent is normally around 3000 FPM at TOC and 2000 FPM nearing 10,000' (typical for the 744, but may be different for your airplane), you can easily make adjustments from those bases.
Once you're below 10,000', the picture should be much clearer. If you're lower than desired, level off, or reduce your rate of descent to 500 FPM if you cannot level. If you're higher than desired, use speedbrakes (if you think you will only need them temporarily) and/or flaps (if you think you'll need them all the way down) to help slow down and/or descend more quickly. I have flown CDA profiles from 30+ miles before CDA was even a buzzword, much less "required". Just hold 240-250 KIAS until you want (or are told) to slow down, and use thrust and/or speedbrakes to get to the 3 deg profile.
Your standard FCOM procedures will give you the rest of your guidelines (e.g., start configuring at 17-20 NM from the airport in the 744). Once you're near the ideal path, you can easily slow down by simply extending flaps and landing gear in the normal sequence while decelerating.
Another advice:
It's a feel thing and not a mental calculation.
It's a feel thing and not a mental calculation.
For slowing down, it's trial and error. It depends alot on the wind and the grossweight with the 737NG but I assume it's the same with the bus. In the beginning, try to slow down in level flight to get to know the energy management of the aircraft
You also give an example, but so did others...
To an extent, for the person who asked the question, it IS "trial and error"! Since he apparently does not yet have a good feel for his airplane, the best he can do is meld his FCOM procedures with any or any mix of the examples, techniques, and guidelines given here. If he is unable to start at 20 NM and 5000' (your single example), he will have to interpolate, find another guideline, and/or calculate a path using his own devices.
Getting TO a standard (or or reasonably close) profile in the "Euro" environment you describe is likely harder than staying on it. However, if you "know" that your initial VNAV rate of descent is normally around 3000 FPM at TOC and 2000 FPM nearing 10,000' (typical for the 744, but may be different for your airplane), you can easily make adjustments from those bases.
Once you're below 10,000', the picture should be much clearer. If you're lower than desired, level off, or reduce your rate of descent to 500 FPM if you cannot level. If you're higher than desired, use speedbrakes (if you think you will only need them temporarily) and/or flaps (if you think you'll need them all the way down) to help slow down and/or descend more quickly. I have flown CDA profiles from 30+ miles before CDA was even a buzzword, much less "required". Just hold 240-250 KIAS until you want (or are told) to slow down, and use thrust and/or speedbrakes to get to the 3 deg profile.
Your standard FCOM procedures will give you the rest of your guidelines (e.g., start configuring at 17-20 NM from the airport in the 744). Once you're near the ideal path, you can easily slow down by simply extending flaps and landing gear in the normal sequence while decelerating.
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Good post Intruder, not a single mention of ToD. And actually some useful advice for the topic at hand
I would add that it's makes most sense to start configuring if you are too high on profile and start slowing down, rather than keep speed and use speed brake when inside 25 nm distance to go.
High on profile:
1) Far away, high altitude: Increase speed and use speed brakes if necessary
2) Close up, low altitude: Slow down and configure.
If there is no possibility to get back on path in the correct energy state, it makes most sense to arrive at the FAP: Too high, but correct speed and configured. Rather that on profile, but too fast and clean.
It's easy the get a dirty aircraft to catch up with the glide slope. And because you are slow, you have more time to work the situation peacefully. It's more work to get a clean aircraft slowed down and configured once glide slope has been captured. And the latter carries a higher risk of a rushed and unstabilised approach.
This is not meant as a contradiction to what I posted in post 5 (which contained more than the one line you quoted):
With the above, I must stress I meant for smaller deviations in speed, but still configured with approach flap setting. If either you or ATC made a major screw up, dirty up and catch the glide from above.
P.s.
@Groucho and Amadis of Gaul:
Once you're below 10,000', the picture should be much clearer. If you're lower than desired, level off, or reduce your rate of descent to 500 FPM if you cannot level. If you're higher than desired, use speedbrakes (if you think you will only need them temporarily) and/or flaps (if you think you'll need them all the way down) to help slow down and/or descend more quickly.
High on profile:
1) Far away, high altitude: Increase speed and use speed brakes if necessary
2) Close up, low altitude: Slow down and configure.
If there is no possibility to get back on path in the correct energy state, it makes most sense to arrive at the FAP: Too high, but correct speed and configured. Rather that on profile, but too fast and clean.
It's easy the get a dirty aircraft to catch up with the glide slope. And because you are slow, you have more time to work the situation peacefully. It's more work to get a clean aircraft slowed down and configured once glide slope has been captured. And the latter carries a higher risk of a rushed and unstabilised approach.
This is not meant as a contradiction to what I posted in post 5 (which contained more than the one line you quoted):
If it doesn't fit correctly, you can either arrive at a wrong height or wrong speed. Always arrive at the right height, and choose speed as your variable.
P.s.
@Groucho and Amadis of Gaul:
