Controlled Descent Approaches - from an ATC point of view
Bellwether&cloudbuster
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Continuous Descent Approaches - from an ATC point of view
Morning all,
Some questions which you experts will no doubt answer in seconds.
1) Are CDA's mandatory in any ATC area?
2) Is it the pilot or ATC that suggest or ask for a CDA usually?
3) What are the usual reasons given by pilots for not accepting a CDA if suggested/wanted by ATC?
I am interested in how the communication is done and whether ATC wish a lot more CDA's were done, or whether it causes them more headaches and they are happy with the low and long approaches?
Thanks in advance,
J
Some questions which you experts will no doubt answer in seconds.
1) Are CDA's mandatory in any ATC area?
2) Is it the pilot or ATC that suggest or ask for a CDA usually?
3) What are the usual reasons given by pilots for not accepting a CDA if suggested/wanted by ATC?
I am interested in how the communication is done and whether ATC wish a lot more CDA's were done, or whether it causes them more headaches and they are happy with the low and long approaches?
Thanks in advance,
J
Last edited by Julian Hensey; 26th Jul 2007 at 10:20.
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They're not Controlled - It's CONTINUOUS Descent Approaches
1) Where I work - yes if achievable. All operators are monitored for CDA compliance and follow up action is taken in terms of communications with the company if CDA compliance falls below a certain level.
2) Neither - see above
3) CDA's tend not to be refused as such. But some airlines are better at doing them than others.
For us it's a distict advantage as you no longer require a "stepped descent" to keep the aircraft inside CAS. You give the aircraft the track miles to run and then start the descent using the "3nm per 1000ft" rule. The resulting profile if correctly flown will keep the aircraft inside CAS with no further input from ATC.
Sad to say some people still haven't grasped the concept, and still push the nose down to 2500fpm when half that is required. There seems to be a belief from some more "experienced" pilots that DME distance overrules the miles that they're given by ATC - this is one part of the culture that needs working on. The introduction of FMS flown P-RNAV approaches will be a great help in this respect.
1) Where I work - yes if achievable. All operators are monitored for CDA compliance and follow up action is taken in terms of communications with the company if CDA compliance falls below a certain level.
2) Neither - see above
3) CDA's tend not to be refused as such. But some airlines are better at doing them than others.
For us it's a distict advantage as you no longer require a "stepped descent" to keep the aircraft inside CAS. You give the aircraft the track miles to run and then start the descent using the "3nm per 1000ft" rule. The resulting profile if correctly flown will keep the aircraft inside CAS with no further input from ATC.
Sad to say some people still haven't grasped the concept, and still push the nose down to 2500fpm when half that is required. There seems to be a belief from some more "experienced" pilots that DME distance overrules the miles that they're given by ATC - this is one part of the culture that needs working on. The introduction of FMS flown P-RNAV approaches will be a great help in this respect.
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Hi there Julian,
not quite sure what you mean by "controlled" descent approaches. I think you might mean continuous descent approaches where by the controller and aircrew work together to achieve a descent profile that will not require the aircraft to level off at an intermediate level until preparing to establish on the ILS.
It is done because the aircraft will be using less fuel and generating less noise if it is in a continuous slow descent than if power was having to be applied to level the aircraft out.
It is achieved (in an ideal environment) firstly by the FMS calculating the top of descent from cruising level for a standard arrival. As the aircraft enters TMA or approach airspace, the controller will give track miles to touchdown according to the traffic pattern and issue descent clearances using the rule of thumb of the aircraft descending 1,000 feet every 3 track miles (roughly the same as a 3 degree glidepath). The pilots then use this information to plan their rate of descent, speeds etc. The ideal scenario is for the aircraft to level out as it captures the localiser, establish on the centreline then capture the glidepath from below.
As said, this is what happens in an ideal environment however with boundaries of different sectors of airspace in the vertical plane, standing agreements between sectors and units, increased holding, bases of controlled airspace and conflicting traffic to take into account, it is somewhat harder but far from impossible to achieve.
Darn, beat me to it chilli.
not quite sure what you mean by "controlled" descent approaches. I think you might mean continuous descent approaches where by the controller and aircrew work together to achieve a descent profile that will not require the aircraft to level off at an intermediate level until preparing to establish on the ILS.
It is done because the aircraft will be using less fuel and generating less noise if it is in a continuous slow descent than if power was having to be applied to level the aircraft out.
It is achieved (in an ideal environment) firstly by the FMS calculating the top of descent from cruising level for a standard arrival. As the aircraft enters TMA or approach airspace, the controller will give track miles to touchdown according to the traffic pattern and issue descent clearances using the rule of thumb of the aircraft descending 1,000 feet every 3 track miles (roughly the same as a 3 degree glidepath). The pilots then use this information to plan their rate of descent, speeds etc. The ideal scenario is for the aircraft to level out as it captures the localiser, establish on the centreline then capture the glidepath from below.
As said, this is what happens in an ideal environment however with boundaries of different sectors of airspace in the vertical plane, standing agreements between sectors and units, increased holding, bases of controlled airspace and conflicting traffic to take into account, it is somewhat harder but far from impossible to achieve.
Darn, beat me to it chilli.
Bellwether&cloudbuster
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Thanks have altered my forum post to continuous descent.
I assume statisically that CDA's are also likely to cause less airproxes if large aircraft are higher up on the descent profile they are statisically unlikely to meet GA aircraft until further into the track miles than if they were low and long.
Are the mandatory CDA's written into regulations or is this is an airspace by airspace approach and if so what grounds do they have for insisting it is done?
I assume statisically that CDA's are also likely to cause less airproxes if large aircraft are higher up on the descent profile they are statisically unlikely to meet GA aircraft until further into the track miles than if they were low and long.
Are the mandatory CDA's written into regulations or is this is an airspace by airspace approach and if so what grounds do they have for insisting it is done?
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NOISE - Extract from the UK AIP entry for East Midlands (EGNX) AD 2.21 - Nouse Abatement Procedures
7 Continuous Descent Approaches
a) Turbo-jet and turbo-prop aircraft are expected to apply continuous descent, low power, low drag approach techniques at all times.
b) Subject to ATC instructions, inbound aircraft are to maintain as high an altitude as practical and adopt a low power, low drag, continuous
descent approach profile. ATC will provide estimated track distance to touchdown to allow pilots to descend at a rate they judge best suited
to achieve continuous descent without using more power or drag than necessary. The object will be to join the glidepath at the appropriate
height for the distance without level flight.
descent approach profile. ATC will provide estimated track distance to touchdown to allow pilots to descend at a rate they judge best suited
to achieve continuous descent without using more power or drag than necessary. The object will be to join the glidepath at the appropriate
height for the distance without level flight.
c) To facilitate these techniques aircraft should be flown no faster than 250 kts from the Speed Limiting Points and below FL100 and 250 kts-
210 kts during the intermediate approach phase. Thereafter speed should managed so as to achieve a continuous descent using as little
power or drag as possible. ATC may impose speed control if required for separation purposes.
210 kts during the intermediate approach phase. Thereafter speed should managed so as to achieve a continuous descent using as little
power or drag as possible. ATC may impose speed control if required for separation purposes.
d) ATC will provide regular range checks. Pilots who require additional track mileage to facilitate a successful CDA should inform ATC as soon
as the requirement is apparent.
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A CDA is achieved by the controller giving an accurate range and the pilot adjusting his rate of descent accordingly so that the GP is intercepted without the ac actually levelling off, well thats the theory.
Some controllers wait until range is about 23/24 miles and then give descent from Min stack.
All CDA's into the TMA airfields are monitored electronically and reported on if not achieved. This is particularly enforced during the night period.
Some controllers wait until range is about 23/24 miles and then give descent from Min stack.
All CDA's into the TMA airfields are monitored electronically and reported on if not achieved. This is particularly enforced during the night period.
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The question posed was 1) are CDA'S mandatory. The correct answer is no, but they are preferable. The airline I work for(non-UK), regard CDA'S with some surprise. Were they to be made mandatory, then more would strive to achieve them and no doubt by management decree or by 'folklore', there would emerge a 'good practice method' of operating CDA's for that particular aircraft type.
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There was another thread on this http://www.pprune.org/forums/showthread.php?t=271870 and we discovered there that Stansted did NOT specify CDAs and Manchester was night only?
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For those that don't know, there are two main reasons for CDAs. Firstly noise. Aeroplanes are noisy things even these days and for airports to maintain the best possible relationship with those who live nearby they have to make every conceivable effort to reduce noise. Aircraft levelling off during the descent make considerably more noise than those on a CDA. The second reason is that a CDA is more fuel efficient.
I don't know what they do at Manch but at Stansted CDAs are the norm on rwy 23 (although some operators are better than others). Due to the design of the current airspace it is not possible to fly a CDA to rwy 05.
I don't know what they do at Manch but at Stansted CDAs are the norm on rwy 23 (although some operators are better than others). Due to the design of the current airspace it is not possible to fly a CDA to rwy 05.
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Thanks for all the answers - another one - at what height does the CDA stop? A "follow the ILS" approach is the same descent profile approximately as a CDA or not?
