Continuous Descent Approaches
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So how often then should a 'Distance to Go' advisory be given, if a Star was not available, or a radr vector had interrupted the Star process.
Also, assuming the latter, can a Star be re-captured by the FMS if the vectoring was for a short term fix scenario only?
Also, assuming the latter, can a Star be re-captured by the FMS if the vectoring was for a short term fix scenario only?
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themwasthe days
Your definition of a CDA seems fine to me, but as has already been mentioned, CDAs mean different things to different people depending upon their location and equipment. So does your definition get across what you want it to?
For example at Heathrow the plates tell us (forgive me if I am teaching the proverbial grandmother to suck eggs!) "... a descent will be deemed to be continuous provided that no segment of flight longer than 2.5nm occurs below 6000' and level flight is interpreted as any segment of flight having a height change of not more than 50ft over a track distance of 2nm or more."
As definitions go, this one is much more prescriptive than the one you gave, but then I don't know if this is actually what you want to achieve as you are bringing STARS into the equation. With reference to Heathrow, CDAs start long after the STAR has finished but most pilots I know attempt to fly a continuous descent from cruise to touchdown. Perverse isn't it!?
G W-H
Your definition of a CDA seems fine to me, but as has already been mentioned, CDAs mean different things to different people depending upon their location and equipment. So does your definition get across what you want it to?
For example at Heathrow the plates tell us (forgive me if I am teaching the proverbial grandmother to suck eggs!) "... a descent will be deemed to be continuous provided that no segment of flight longer than 2.5nm occurs below 6000' and level flight is interpreted as any segment of flight having a height change of not more than 50ft over a track distance of 2nm or more."
As definitions go, this one is much more prescriptive than the one you gave, but then I don't know if this is actually what you want to achieve as you are bringing STARS into the equation. With reference to Heathrow, CDAs start long after the STAR has finished but most pilots I know attempt to fly a continuous descent from cruise to touchdown. Perverse isn't it!?
G W-H
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Guy's,
Was beginning to wonder whether any of the contributors to this thread had any experience of CDA's in the real world until Scrogg's and G W-H's comments. The idea of idle thrust descents from cruise level to 1000' AGL within busy UK/European airspace is totally unrealistic, and rather ignorant (although that's not to say it cant be done in places!)
CDA's seem to be the flavour of the month at the moment in terms of environmental issues, or to put it simply, reducing noise. Definitions of CDA's that i've seen are similar to that suggested by G W-H - they mention something with regards to the pilot, after leaving a given fix/level, should judge his rate of descent such as to arrive at final approach without recourse to level flight.
Although I consider it good handling & airmanship to practice CDA's on every approach, in many cases it is just not possible. Aerodromes that specify such approaches are generally well set up to support them - regular estimates of track miles remaining are provided on leaving the holding fix/STAR end waypoint, all of which makes the execution somewhat simpler. Elsewhere, the task is a bit more complex.
In terms of the automatics, I can only say that the FMS on the scarebuses that I fly are not really capable of CDA approaches. The boxes have a nasty habit of prescribing level-off's in their profiles to allow deceleration (e.g. 250kts to min clean speed etc). Subsequent flight in managed descent (Airbus V-NAV) results in these level-off's. Thus, invariably, CDA's are flown in Speed - V/S modes, or if one is feeling particularly sporty, via manual flight.
I also totally agree with alf5071h's comments with regard's to NPA's - they should all be flown without level-off, where possible. However, i have always referred to such approaches as "balanced, stabilised approaches", not CDA's. Would be interested to hear other people’s comments!
Regards,
Cuban_8
Was beginning to wonder whether any of the contributors to this thread had any experience of CDA's in the real world until Scrogg's and G W-H's comments. The idea of idle thrust descents from cruise level to 1000' AGL within busy UK/European airspace is totally unrealistic, and rather ignorant (although that's not to say it cant be done in places!)
CDA's seem to be the flavour of the month at the moment in terms of environmental issues, or to put it simply, reducing noise. Definitions of CDA's that i've seen are similar to that suggested by G W-H - they mention something with regards to the pilot, after leaving a given fix/level, should judge his rate of descent such as to arrive at final approach without recourse to level flight.
Although I consider it good handling & airmanship to practice CDA's on every approach, in many cases it is just not possible. Aerodromes that specify such approaches are generally well set up to support them - regular estimates of track miles remaining are provided on leaving the holding fix/STAR end waypoint, all of which makes the execution somewhat simpler. Elsewhere, the task is a bit more complex.
In terms of the automatics, I can only say that the FMS on the scarebuses that I fly are not really capable of CDA approaches. The boxes have a nasty habit of prescribing level-off's in their profiles to allow deceleration (e.g. 250kts to min clean speed etc). Subsequent flight in managed descent (Airbus V-NAV) results in these level-off's. Thus, invariably, CDA's are flown in Speed - V/S modes, or if one is feeling particularly sporty, via manual flight.
I also totally agree with alf5071h's comments with regard's to NPA's - they should all be flown without level-off, where possible. However, i have always referred to such approaches as "balanced, stabilised approaches", not CDA's. Would be interested to hear other people’s comments!
Regards,
Cuban_8
V/S 500' / Min seems to work quite well at LGW and LHR coming out of the hold or thereabouts. LGW always seems to be a few miles short of actuality if they offer you track miles to run. I think you can fly level for about 4 miles below 4000' and only need 100fpm down at any stage so it's not too onerous.Anyway, it gives the 'cruiser' in the bunk another few minutes sleep!
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I would imagine that the ATC requirement for no less than 500fpm would also come in to the equation. Something i strive for but not always achieving. As an aside whilst using VNAV the other day it climbed 60ft to enable the speed reduction to 250kts. Try to avoid using it on most sectors, much prefering to use FLCH with speed reduction at approx 2-2500 above required platform. B777 aicraft, how does the bus compare.
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For those interested in CDAs, the latest figures I have via the company newsletter for May 2004 are:
Successful CDAs into Heathrow (+/-2% as I am reading off a slightly indistinct bar graph)
Aer Lingus 92%
Air France 70%
Air India 96%
Alitalia 70%
American 86%
British Airways 96%
BMI 95%
Cathay Pacific 79%
Emirates 76%
Iberia 74%
KLM 83%
Lufthansa 66%
Qantas 74%
Singapore 95%
United Airlines 67%
Virgin 92%
It just goes to show - our CDAs are being watched!
Continuously yours
G W-H
Successful CDAs into Heathrow (+/-2% as I am reading off a slightly indistinct bar graph)
Aer Lingus 92%
Air France 70%
Air India 96%
Alitalia 70%
American 86%
British Airways 96%
BMI 95%
Cathay Pacific 79%
Emirates 76%
Iberia 74%
KLM 83%
Lufthansa 66%
Qantas 74%
Singapore 95%
United Airlines 67%
Virgin 92%
It just goes to show - our CDAs are being watched!
Continuously yours
G W-H
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A CDA has nothing to do with iddle thrust but with not leveling off.
Minimum drag approach is a different thing and means minmum flap and gear up for as long as possible. It does amaze me how some people do ask for gear down 12 miles out and at 3 am...
An iddle thrust descent all the way to 1000', although ideal in terms of fuel burn, can easily degenerate into a rushed approach. I think that iddle descent as far as possible but with partial thrust descent segments in the last 20 miles gives a better margin for error. ATC normally scuppers the plan anyway.
In the UK it is described a good practice to do a CDA whenever possible. (Jeppessen country differences)
The 500fpm minimum rate only applies above the Transition Level.
Minimum drag approach is a different thing and means minmum flap and gear up for as long as possible. It does amaze me how some people do ask for gear down 12 miles out and at 3 am...
An iddle thrust descent all the way to 1000', although ideal in terms of fuel burn, can easily degenerate into a rushed approach. I think that iddle descent as far as possible but with partial thrust descent segments in the last 20 miles gives a better margin for error. ATC normally scuppers the plan anyway.
In the UK it is described a good practice to do a CDA whenever possible. (Jeppessen country differences)
The 500fpm minimum rate only applies above the Transition Level.
With regards to CDA's, is the descent conducted through the flight management computer and is it this that maintains idle thrust throughout the descent or does the pilot have to make sure that idle thrust is acheived through out this? Im confused as to weather the thrust for descent has to be programmed into the FMC for a CDA beforehand?
Is it possible for a CDA be achieved accuratly soley by using the MCP/FCU?
Many Thanks
Dan
Is it possible for a CDA be achieved accuratly soley by using the MCP/FCU?
Many Thanks
Dan
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The FMC will calculate a descent based on flying level for as long as possible and then descending at Iddle thrust to meet the next altitude and speed constraint while maintaining the programed descent speed (normaly a function of the cost index + winds). The calculations are further refined if you tell the FMC the winds in the descent, the local QNH and through wich levels you will be using any ainti-ice (higher thrust setting required for the ainti-ice).
With some practice you can achieve this manually as well. When radar vectored into a busy airfiled you have to guess the track miles left and continuosly adjust your rate of descent. Flexibility is the key and postive actions to control the descent path. As you are normally given an assigned speed you will often be flying partial thrust (if they vector you along a longer route than planed) or with the aid of the speedbrake (if the give you a shorter route of a much reduced speed).
I hope this helps....
With some practice you can achieve this manually as well. When radar vectored into a busy airfiled you have to guess the track miles left and continuosly adjust your rate of descent. Flexibility is the key and postive actions to control the descent path. As you are normally given an assigned speed you will often be flying partial thrust (if they vector you along a longer route than planed) or with the aid of the speedbrake (if the give you a shorter route of a much reduced speed).
I hope this helps....
Thanks a lot for the reply, i'm getting a clearer perception of how it works!
However what would happen if you were instructed to level off at, say FL150 during a CDA and then descend to another flight level a couple of minutes later. Would the FMC automatically calculate a new aispeed to maintain idle thrust (and an appropriate descent rate) throughout the descent to the next cleared level?
When VNAV is selected (on the 737 series), does the autopilot always fly a CDA or is there other modes that can be used from the FMC?
Many Thanks
Dan
However what would happen if you were instructed to level off at, say FL150 during a CDA and then descend to another flight level a couple of minutes later. Would the FMC automatically calculate a new aispeed to maintain idle thrust (and an appropriate descent rate) throughout the descent to the next cleared level?
When VNAV is selected (on the 737 series), does the autopilot always fly a CDA or is there other modes that can be used from the FMC?
Many Thanks
Dan
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You're getting a bit caught up in the different approaches. You can have the Precision RNAV trials currently underway at LHR. You can have CDA radar vectored approaches and non-CDA radar vectored approaches. For PRNAV approaches, it is advisable to use speed/VS control to allow maximum control and monitoring. The same for CDA approaches. At LHR, they apply below 7000' or Transition Level. You get advised at some stage of approximate distance to go. Idle power is irrelevant- the aim is to not fly level or if you do have to fly level through descending too rapidly, allow the aeroplane to slow down to minimise power before taking up descent again. You must continually assess how you are positioned on the approach with distance to go and altitude to keep the descent going at a sensible rate to allow continual descending. If you get over-involved with trying to play with FMS programming whilst doing this, you are allowing one pilot's attention to be too focused inside the aeroplane. Speed/VS does it- period.
Oh right I see now. I was getting confused as when I watched a few videos, the aircraft has been engaged in VS and Speed mode throughout the latter stages of the descent and not in VNAV mode.
I suppsose playing around with the FMC during lower levels can be very distracting and is much more advisable to use the MCP.
How does the controller know what descent you are using - filed on the flight plan?
I tried various descents using the FMC on my flight sim addon and found it much easier to switch to the MCP below FL 80. Using the VNAV mode above FL 80 to fly the programmed descent was very accurate - impressive!
Many Thanks
Dan
I suppsose playing around with the FMC during lower levels can be very distracting and is much more advisable to use the MCP.
How does the controller know what descent you are using - filed on the flight plan?
I tried various descents using the FMC on my flight sim addon and found it much easier to switch to the MCP below FL 80. Using the VNAV mode above FL 80 to fly the programmed descent was very accurate - impressive!
Many Thanks
Dan
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Certain airfields require CDAs. When controllers start giving you radar headings and you know a CDA is required on the landing booklet, then it is obvious. At other airfields where CDAs are not required, I still try to do them to stop the cabin pitching up all the time- for comfort the passengers will just feel a steady descent. In the US where idle power descents are required, you just obey their requirements. Nobody instructs you, it is assumed you know what you should be doing.
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Please allow me to formulate some remarks on the CDA issue.
Concept
As the purpose of CDA is noise reduction, the non existence of level flight is not relevant. The focus should be on the avoidance of high thrust settings at lower altitudes. Consequently, level flight with the purpose of decelerating the aircraft with idle or near idle thrust meets the CDA purpose (the CDA acronym is therefore not an ideal term).
Regulatory framework
CDA execution is strongly aircraft type and aircraft weight related. The pilot is in the best position to judge the minimum noise CDA flight path. He will do that, not on the 3° flight path assumption, but rather on the more accurate FMS computation which is based on the energy concept. Therefore one single CDA profile is not feasible. The pilot should be given enough freedom to determine an ideal flight path in function of the circumstances.
Low power/low drag
Low power low drag approaches have two distinct purposes:
Low power = idle descent and deceleration, means following the ideal profile according to the aircraft weight, type and weather (wind).
Low drag = the use of clean optimum speeds (low speeds) as long as possible and extend drag devices as late as possible. (gear, flaps, speed brakes)
a. Keeping an aircraft high on profile will cause it to use drag devices such as speed brakes and gear (or high speed) which will dramatically increase the noise produced by the aircraft. An aircraft low on profile will need more than idle trust to recover the profile, also increasing the noise footprint.
b. In case of RNAV arrivals, (FRA type) even when RV will be issued, it is advantageous to assign an arrival route matching as closely as possible with the expected RV pattern as early as possible. DTG is very valuable information, but a correct route programmed in the FMS is even more accurate. The FMS is not able to calculate a profile solely based on DTG.
c. Phraseology to issue a CDA clearance is very important. Since CDA involves a descent, it should be clear to which extend the profile can be followed. It is my opinion that a normal descent clearance and altitude should be given. Is CDA an Approach or an Arrival? This very important to understand; an approach ends on the ground. An arrival ends at the start of an approach procedure. After receiving an approach clearance, a descent according to the procedure can be made without a specific descent clearance. This is not so with an arrival where specific descent clearances should be issued, whatever the altitude constraints might be. Confusion must be avoided because vertical separation and obstacle clearance is a safety critical issue. It is my opinion that CDA should be considered as an arrival. This would avoid confusion and avoid extensive review of ICAO material.
Aircraft operations
The energy concept used by the FMS to calculate the optimum profile is very important and needs to be understood by CDA procedure designers. Speed is as important as altitude and DTG. Controllers do sometimes issue impossible clearances because of the lack of understanding regarding the energy concept.
Final Approach
The moment of “gear down” is dependant on specific airline procedures. Aircraft manuals (at least for 737 and 320) recommend gear extension at 3000 ft AGL. This is not followed by most airlines which (regarding Low drag low noise policy) recommend gear extension in the range of 1500 to 2500 ft AGL. Low visibility procedures will require the standard 3000 ft as per aircraft manual. Tailwind might force the pilot to lower the gear early because deceleration is not possible with strong tailwind on a 3° flight path. The 160 kts restriction at the OM can not always be met, especially with heavy aircraft and tailwind. In case of non-precision approaches, approach configuration is required as from start IAP or 3000 ft AGL.
Base leg
Obviously, a downwind route is more sensitive regarding to changing DTG than a straight in route. Consequently, the issuance of a specific lateral route (or DTG) is more important in case of downwind routes or base leg routes.
Effect of the wind
This is a very important issue. It should be understood that flexibility in the profile is required in order to meet with the different wind situations. If not, increased noise because of drag devices or engines will be the result. Wind speed is usually much stronger at altitude than on the ground.
ATC system overview
Regarding speed control: once on a 3 degree profile, speed reduction is difficult without extra drag devices and is also much slower compared to a situation where descent slope can be (temporary) decreased or where a small portion of level flight can be included. Most Aircraft Operating manuals recommend Glide Slope interception from below. Interception from above is difficult, creates high flight deck workload and often leads to rushed or unstabilised approaches.
Manuals
See remark on the energy concept.
Concept
As the purpose of CDA is noise reduction, the non existence of level flight is not relevant. The focus should be on the avoidance of high thrust settings at lower altitudes. Consequently, level flight with the purpose of decelerating the aircraft with idle or near idle thrust meets the CDA purpose (the CDA acronym is therefore not an ideal term).
Regulatory framework
CDA execution is strongly aircraft type and aircraft weight related. The pilot is in the best position to judge the minimum noise CDA flight path. He will do that, not on the 3° flight path assumption, but rather on the more accurate FMS computation which is based on the energy concept. Therefore one single CDA profile is not feasible. The pilot should be given enough freedom to determine an ideal flight path in function of the circumstances.
Low power/low drag
Low power low drag approaches have two distinct purposes:
Low power = idle descent and deceleration, means following the ideal profile according to the aircraft weight, type and weather (wind).
Low drag = the use of clean optimum speeds (low speeds) as long as possible and extend drag devices as late as possible. (gear, flaps, speed brakes)
a. Keeping an aircraft high on profile will cause it to use drag devices such as speed brakes and gear (or high speed) which will dramatically increase the noise produced by the aircraft. An aircraft low on profile will need more than idle trust to recover the profile, also increasing the noise footprint.
b. In case of RNAV arrivals, (FRA type) even when RV will be issued, it is advantageous to assign an arrival route matching as closely as possible with the expected RV pattern as early as possible. DTG is very valuable information, but a correct route programmed in the FMS is even more accurate. The FMS is not able to calculate a profile solely based on DTG.
c. Phraseology to issue a CDA clearance is very important. Since CDA involves a descent, it should be clear to which extend the profile can be followed. It is my opinion that a normal descent clearance and altitude should be given. Is CDA an Approach or an Arrival? This very important to understand; an approach ends on the ground. An arrival ends at the start of an approach procedure. After receiving an approach clearance, a descent according to the procedure can be made without a specific descent clearance. This is not so with an arrival where specific descent clearances should be issued, whatever the altitude constraints might be. Confusion must be avoided because vertical separation and obstacle clearance is a safety critical issue. It is my opinion that CDA should be considered as an arrival. This would avoid confusion and avoid extensive review of ICAO material.
Aircraft operations
The energy concept used by the FMS to calculate the optimum profile is very important and needs to be understood by CDA procedure designers. Speed is as important as altitude and DTG. Controllers do sometimes issue impossible clearances because of the lack of understanding regarding the energy concept.
Final Approach
The moment of “gear down” is dependant on specific airline procedures. Aircraft manuals (at least for 737 and 320) recommend gear extension at 3000 ft AGL. This is not followed by most airlines which (regarding Low drag low noise policy) recommend gear extension in the range of 1500 to 2500 ft AGL. Low visibility procedures will require the standard 3000 ft as per aircraft manual. Tailwind might force the pilot to lower the gear early because deceleration is not possible with strong tailwind on a 3° flight path. The 160 kts restriction at the OM can not always be met, especially with heavy aircraft and tailwind. In case of non-precision approaches, approach configuration is required as from start IAP or 3000 ft AGL.
Base leg
Obviously, a downwind route is more sensitive regarding to changing DTG than a straight in route. Consequently, the issuance of a specific lateral route (or DTG) is more important in case of downwind routes or base leg routes.
Effect of the wind
This is a very important issue. It should be understood that flexibility in the profile is required in order to meet with the different wind situations. If not, increased noise because of drag devices or engines will be the result. Wind speed is usually much stronger at altitude than on the ground.
ATC system overview
Regarding speed control: once on a 3 degree profile, speed reduction is difficult without extra drag devices and is also much slower compared to a situation where descent slope can be (temporary) decreased or where a small portion of level flight can be included. Most Aircraft Operating manuals recommend Glide Slope interception from below. Interception from above is difficult, creates high flight deck workload and often leads to rushed or unstabilised approaches.
Manuals
See remark on the energy concept.
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G W-H
The need for a widening of the definition seems obvious to me, as the narrow focus applied at LHR makes its application in other arenas difficult. The comments to date would seem to indicate that the level flight segment to be of no consequence to the purpose of a CDA, which for me is efficiency and environment. Efficiency in ATM by way of STARs promulgated that meet system capabilities WRT fuel burn, pax comfort, and low workload (ATC and F/C), whilst environment wins with low emission and noise footprints. If radar vectoring is required, then a close proximation of a STAR profile, or “regular” track followed, and accurate updated distance to go info.
FMS issues seem to be something else, in that there would seem to be an issue of level flight segment for deceleration purposes, as well as the glide slop intercept from beneath.
Trying to develop a global procedure that is realistic and flyable is not easy, and that was the purpose of being less prescriptive. Trying to gather a consensus – well that’s another issue.
Egg sucking grannie? – I am always ready to listen and learn. Keep it comin!
The need for a widening of the definition seems obvious to me, as the narrow focus applied at LHR makes its application in other arenas difficult. The comments to date would seem to indicate that the level flight segment to be of no consequence to the purpose of a CDA, which for me is efficiency and environment. Efficiency in ATM by way of STARs promulgated that meet system capabilities WRT fuel burn, pax comfort, and low workload (ATC and F/C), whilst environment wins with low emission and noise footprints. If radar vectoring is required, then a close proximation of a STAR profile, or “regular” track followed, and accurate updated distance to go info.
FMS issues seem to be something else, in that there would seem to be an issue of level flight segment for deceleration purposes, as well as the glide slop intercept from beneath.
Trying to develop a global procedure that is realistic and flyable is not easy, and that was the purpose of being less prescriptive. Trying to gather a consensus – well that’s another issue.
Egg sucking grannie? – I am always ready to listen and learn. Keep it comin!
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Before T/d,our sops suggest to use Capture mode in descent page when on top of a 3 deg descent at 290kts.
Gives us a practical 1000ft min initially to avoid and Tcas RA in RVSM.
In Vnav it captures then the path.
However,in many airports speeds restrictions are cleared out and short cuts given..so I often use LVL Change once airspeed is set and established in descent to avoid disconfort to PAX.
Boeing recommends LVL Change then VS in the last 1000ft which will allow you a precise glide capture...avoiding unecessary increase of power in noise sensitive areas.
Speedbrakes are used primarly in Egypt and greece...mmhhhh...
Safe Flying,
M.85
Gives us a practical 1000ft min initially to avoid and Tcas RA in RVSM.
In Vnav it captures then the path.
However,in many airports speeds restrictions are cleared out and short cuts given..so I often use LVL Change once airspeed is set and established in descent to avoid disconfort to PAX.
Boeing recommends LVL Change then VS in the last 1000ft which will allow you a precise glide capture...avoiding unecessary increase of power in noise sensitive areas.
Speedbrakes are used primarly in Egypt and greece...mmhhhh...
Safe Flying,
M.85
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themwasthe days
I think that I see what you are getting at. You are looking to design a procedure for arriving aircraft which is both efficient and minimises environmental impact. Since some respondants have opined that a level segment is not always a bad thing - a CDA might not be what you are after!!
If you turned up at my door today and asked my opinion, I would say that since you are trying to achieve an awful lot from one procedure, the CDA is the way ahead and that in my experience Heathrow and Gatwick (at least a couple of years ago) set the gold standard.
ATC Aspects
The STARs seem to offer an idle descent whilst operating at "normal" speeds. The ATC procedures (agreed levels etc) allow the descent to be continuous under most circumstances.
The radar vectoring by LL DIR follows a path which is fairly predictable to regular visitors. The speed control they use 220/210, 180, 160 seems to fit well with the majority of types operated into the airport. London TMA airports are the only places where the pilots are always given a very good idea of the number of miles to run - this is the key factor in achieving the CDA.
Flight Deck Aspects
I really would not get too worried or bogged down in FMS operation, autopilot mode etc. I think I have probably flown various parts of the approach in every possible mode.
With the sensible profiles that have been chosen for Heathrow when a continuous descent from cruise starts to become impossible because of holding, it is often still possible to keep the thrust at idle and slow down a bit each time the aircraft levels.
Drawbacks and Areas for Improvement
- A level of holding is required to maximise runway utilisation and this occurs at low level which is inefficiet in fuel. If you were starting again it might be worth trying to hold a few more miles out and higher up.
- The lateral track around which we are vectored is known only to regular visitors. I would publish a nice glossy briefing showing the tracks typically followed with reference to waypoints held by the FMS (eg LON, LCY, WOD, KILBA etc). Some pilots actually draw a "route" in the FMC based on what they have flown before and referenced to navaids (eg BIG270/10 etc). I would publish a typical set of these in the brouchure.
-Slightly off topic but, I would have the tower ATSA call TC SW ATSA every time something of operational importance is added to the arrival ATIS (eg "severe icing FL80 at LAM" or "moderate turbulence below FL100 at OCK"). The ATSA could then tell the traffic manager, who could chinagraph it on to that laminated sheet which tells the TMA controller the average delay. At least then we pilots would not think that the TMA controller is trying to kill us when he/she clears us to a level at which to hold that the ATIS says is nasty!!
Just my thoughts
G W-H
I think that I see what you are getting at. You are looking to design a procedure for arriving aircraft which is both efficient and minimises environmental impact. Since some respondants have opined that a level segment is not always a bad thing - a CDA might not be what you are after!!
If you turned up at my door today and asked my opinion, I would say that since you are trying to achieve an awful lot from one procedure, the CDA is the way ahead and that in my experience Heathrow and Gatwick (at least a couple of years ago) set the gold standard.
ATC Aspects
The STARs seem to offer an idle descent whilst operating at "normal" speeds. The ATC procedures (agreed levels etc) allow the descent to be continuous under most circumstances.
The radar vectoring by LL DIR follows a path which is fairly predictable to regular visitors. The speed control they use 220/210, 180, 160 seems to fit well with the majority of types operated into the airport. London TMA airports are the only places where the pilots are always given a very good idea of the number of miles to run - this is the key factor in achieving the CDA.
Flight Deck Aspects
I really would not get too worried or bogged down in FMS operation, autopilot mode etc. I think I have probably flown various parts of the approach in every possible mode.
With the sensible profiles that have been chosen for Heathrow when a continuous descent from cruise starts to become impossible because of holding, it is often still possible to keep the thrust at idle and slow down a bit each time the aircraft levels.
Drawbacks and Areas for Improvement
- A level of holding is required to maximise runway utilisation and this occurs at low level which is inefficiet in fuel. If you were starting again it might be worth trying to hold a few more miles out and higher up.
- The lateral track around which we are vectored is known only to regular visitors. I would publish a nice glossy briefing showing the tracks typically followed with reference to waypoints held by the FMS (eg LON, LCY, WOD, KILBA etc). Some pilots actually draw a "route" in the FMC based on what they have flown before and referenced to navaids (eg BIG270/10 etc). I would publish a typical set of these in the brouchure.
-Slightly off topic but, I would have the tower ATSA call TC SW ATSA every time something of operational importance is added to the arrival ATIS (eg "severe icing FL80 at LAM" or "moderate turbulence below FL100 at OCK"). The ATSA could then tell the traffic manager, who could chinagraph it on to that laminated sheet which tells the TMA controller the average delay. At least then we pilots would not think that the TMA controller is trying to kill us when he/she clears us to a level at which to hold that the ATIS says is nasty!!
Just my thoughts
G W-H
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Level flight is of little consequence to CDA, as suggested, but is relevant to the need for careful and accurate management of the vertical profile, as has been suggested elsewhere.
Also, ICAO Doc8168 quotes in vectoring to the ILS for parallel approaches”:
“The vector shall also be such as to enable the aircraft to be established on the ILS localizer course or MLS final approach track in level flight for at least 3.7 km (2.0 NM) prior to intercepting the ILS glide path or specified MLS elevation angle”.
This would seem to indicate to me that some element of level flight is mandated for such operations. Y/N?
Also, ICAO Doc8168 quotes in vectoring to the ILS for parallel approaches”:
“The vector shall also be such as to enable the aircraft to be established on the ILS localizer course or MLS final approach track in level flight for at least 3.7 km (2.0 NM) prior to intercepting the ILS glide path or specified MLS elevation angle”.
This would seem to indicate to me that some element of level flight is mandated for such operations. Y/N?
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N. The whole point of CDA is to avoid any level flight with power on. The quote you have brought up must not be for CDA approaches! There is no point or advantage in level flight before intercepting final descent- you will be at about 2500 feet with high power on, flaps out, possibly gear down. What have you achieved? The idea of CDA is to steadily descend as required so as not to fly level with power on creating noise and unnecessarily pitching the cabin. All it takes is the pilot assessing his altitude and distance to touchdown and managing a steady descent. It is not hard!
Giles- CDA only applies in the lower stages of the approach- I can't remember if it's 7000' or below Transition Level. It is not practical higher up with so many height constraints.
Giles- CDA only applies in the lower stages of the approach- I can't remember if it's 7000' or below Transition Level. It is not practical higher up with so many height constraints.
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Notso
A CDA actually applies from 6000' (see the definition I gave a couple of pages ago) in the Heathrow case.
I don't know why you think it is impracticable from higher up - we do it every day, holding or not. 757/767 - programme the FMC with M0.8/290kts in the descent page, standard height constraints on the way down, 250kts FL80+ 12nm before the fix, 210/220kts FL80 at the fix, start the descent a bit before the machine tells you to - works a treat!
(I do agree it can't always be done, but themwasthe days seemed to be looking for ideas and I felt that Heathrow was a good a place as any to start).
G W-H
A CDA actually applies from 6000' (see the definition I gave a couple of pages ago) in the Heathrow case.
I don't know why you think it is impracticable from higher up - we do it every day, holding or not. 757/767 - programme the FMC with M0.8/290kts in the descent page, standard height constraints on the way down, 250kts FL80+ 12nm before the fix, 210/220kts FL80 at the fix, start the descent a bit before the machine tells you to - works a treat!
(I do agree it can't always be done, but themwasthe days seemed to be looking for ideas and I felt that Heathrow was a good a place as any to start).
G W-H