CDA's

[drop kick]

Does anyone know a simply rule of thumb for flying a CDA?:sad:

[fireflybob]

Think this has been discussed in a thread previously.

One of the tips I have is (assuming you are at the correct height for track distance from touchdown) is to monitor the groundspeed especially when being given heading changes since, generally, the wind component will be changing and therefore the groundspeed. It's also likely that you are configuring to intermediate flap setting with airspeed (and hence groundspeed) changing.

Take the groundspeed and multipy by 5 (or divide by 2 and add a nought) and thats the rate of descent you need to maintain the path until you intercept the ILS G/s. (So use V/S mode)

[CAT3C AUTOLAND]

Good advice from FFBob, but it will only work for a 3 degree glide, where you are trying to maintain around a descent rate of approx 320ft per mile.

I assume you are referring to flying jets when doing your CDA's? There are various ways of doing it. As FFBob says monitor your ground speed and adjust you rate of descent accordingly, either using speed or VS depending on your configuartion, ATC speed constraints, and the part of your approach you are flying.

A simply way of planning your approach from high altitude initially would be to multiply you height above the ground by 3, have a look at your speed and take approximately 10 kts per mile to slow down, and that will be the track miles required. You can monitor this all the way down until you get yourself either on a wide base, or down wind, then you can start to refine it. You will develop your 'spidey sense' as you get more experience :).

[drop kick]

Thanks Guys appreciate it, strange isn't that what we used to do before we had magenta dots! All comming back to me now:ok:

[Rainboe]

I take absolutely no notice of groundspeed! Either draw a 10 mile ring, or use the Centre fix. Aim to be at the ring at 3000'AAL with VS. That way, it doesn't matter what your GS is, just fly VS as desired. You can estimate track miles to go and make appropriate allowances if you are low or high. Just aim for minimal or no level flying with a ROD greater than average 200fpm. You don't often start out flying a CDA on the ideal 3 degree slope, and you will probably be on a base leg or downwind anyway, so ALWAYS fly CDAs in VS mode. Be ready if you are extended downwind to immediately reduce ROD, or if you cut in early, get a faster descent going and extend flap. Just aim for a point on extended final approach where you will be at a desired altitude.

The whole point of them is for noise and fuel saving, so don't go extending gear or unnecessary flap above 1500'AAL as well!

[Agaricus bisporus]

strange isn't that what we used to do before we had magenta dots! All comming back to me nowhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

So good 'ol Rainbow pitches in with the lazyest way possible using the FMC, which is apparently how the question arose in the first place, making a lot of unwarranted assumptions (such as that the poster even has one...) guaranteeing the knowledge based process atrophies and becomes forgotten, as quoted above...and then carries on to describe processes that I'm certain will be completely contrary to most companies' SOPs.

Level off at MDA? You mean to say anyone still allows this? What kind of "continuous" descent is that??? What kind of sloppy, gash flying leaves you with a level sector at that point anyway? Doesn't sound as if you should even take your own advice!

[ItsAjob]

Yes they are a load of old tosh to cater for the noise moaners. What do you get if you do it; a medal?

It used to be done properly when the airspace permitted, ie throttles closed at top of descent and not touched until on finals. - Like a pro!

[411A]

It used to be done properly when the airspace permitted, ie throttles closed at top of descent and not touched until on finals.

It still is in many circumstances, busy airspace...or not.
Level off at MDH? You mean to say anyone still allows this?


Actually MDA, nevertheless, yes, not only is it sometimes necessary, it appears to be a lost art for the less-informed/skilled.:rolleyes:

[Agaricus bisporus]

Hard to see how a level sector can ever be necessary if the approach is flown accurately, and to assist those in the "less informed" or perhaps dinosaur category, many companies simply forbid it.

[Rainboe]

Where did I recommend level flying? Do you understand what we are talking about? I am talking about Continuous Descent Approaches- the clue is in the 'C' word. At the front. If you understood what we are talking about, you might twig that below Transition Level, the idea is that whatever your DTG (Distance To Go) to touchdown, you need to set an appropriate RAD (Rate Of Descent) to avoid level flight (ie a ROD<200fpm). You cannot do this at all well unless you use VS mode. Anyone who goes heads-down programming VNAV to try and do it (clumsily) in a terminal area is making a big mistake.

What nonsense are you talking about- making general accusations of 'contravening SOPs' Are you quite clear now? Sometimes the idiots just can't be held back! VS mode was standard CDA procedure on ALL the CDAs I've seen and flown on 747s, 757s and 737s. To the 'Ignore bin' for you, my friend! You are out of your depth! Any pilot who knows what we are talking about here will know my statement Just aim for a point on extended final approach where you will be at a desired altitude. refers to being on the 3 degree slope at a known distance so you can complete your final approach descent without flying level! Not hard, is it?

[Agaricus bisporus]

Just aim for minimal or no level flying clearly states that a level sector is acceptable.

don't go extending gear or unnecessary flap above 1500'AAL
Well, that'll be contrary to some/several/many companies SOPs then, won't it?

VS mode was standard CDA procedure on ALL the CDAs I've seen and flown on 747s, 757s and 737s

Er, never come across RNAV/overlay approaches flown entirely in VNAV - the way to ensure all is continuous without "clumsy" VS. Now, just who's out of his depth here???

I concede your're dead right about the "toxic" bit though.

[Rainboe]

You appear to have unresolved 'hostility issues'! I cannot believe a simple discussion about CDAs was driven to such a personal willy-waving level- all I did was offer advice based on my practice, which is the only way I have seen it done by anybody. I don't know what you fly, but it is evidently something totally different. Frankly, pathetic and childish. Good day Sir.

[exeng]

Rainboe used to pretty good at CDA approaches when I used to fly with him - he very patiently used to explain what he was doing and why he was doing it.

He, along with others, taught me how to manage my energy in a manner that was both safe, efficient and quiet.

So it just may be that you may also learn something if you read his posts a little more carefully.


Regards
Exeng

[jb5000]

Agaricus bisporus,

You appear to have misinterpreted 'minimal or no level flying' to have something to do with MDA. Clearly it doesn't. Rainboe was obviously referring to the time between the transition level and the glideslope (or descent inbound on the final approach track).

I've noticed all of your posts are generally fairly uninformative and hostile, particularly over on the 'Logging FO time' thread. Do you fancy yourself as a bit of a troll or are you just that way in real life as well?

All the best.

[gatbusdriver]

For the purpose of the CDA league tables that are put together, I believe it was a minimum V/S of 400fpm and I think it was a level flight segment of 2nm was allowed (I could very well be wrong).

[Rainboe]

I believe you need to maintain more than 200fpm and a level segment of less than about 2.5 miles to qualify. Nobody has ever explained how the recording is made

[JAR]

From this link:

Arrivals Code of Practice (http://www.dft.gov.uk/pgr/aviation/environmentalissues/arrivalscodeofpractice/)


2. From Transition Altitude, an arrival containing no level flight or
one phase of level flight not longer than 2.5nm is classified
as a CDA.
3. The minimum rate of descent of 500fpm does not apply below
Transition Altitude.

[411A]

Clearly, Agaricus bisporus, is one of those 'newbys' who, does not know how it is done in other companies, and therefore, is ignorant of others procedures, IE: doesn't know s**t from shinola.
Suggest for the concerned, ignoring is the best alternative.

[Brian Abraham]

411A, bottom of page, in green. Maybe, perhaps?? ;)

[411A]

411A, bottom of page, in green. Maybe, perhaps??

More than likely.:}

[Rainboe]

It's great how one poster with some sort of private issue (and chip on his shoulder about something) can terminate a sensible discussion about something as bland as CDAs by trying to make it into some sort of 'you're wrong and don't know what you're talking about!' when he himself appears to have grabbed the wrong end of the stick. Now, everybody is scared to chip in. Well done Agricola Bisporola or whatever you call yourself! You are a twerp. Go educate yourself before becoming so loud.

[The Real Slim Shady]

If you ALWAYS fly a CDA in VS and with a ROD greater than average 200fpm it won't work for 2 reasons: firstly, the min ROD is usually 450fpm for the purpose of calculating the level segent, and since VS is a controlling mode your IAS and hence GS will be a function of the VS ( ignoring any wind effect).

I find it easier to use LVL CHG and adjust the MCP SPD to control the ROD.

Nevertheless, VS is another tool in the box and can, and should be used if and when needed.

The aim is to arrive at DH configured and stable for the landing: to achieve that we need to be at GS intercept, ideally at LOC capture, at around 180kts with, in the 737NG, Flap 5.

Knowing where that position is in space allows you build "windows" that you must make in the descent.

5 track miles from the GS / LOC intercept you need to be 1500ft above the intercept as a maximum ( 300ft per mile): if you are at 220kts at this point in LVL CHG you may need to use speedbrake to reduce the IAS for flap extension - it all depends on your company SOPs.

My preference is to have Flap 1 out before commencing the CDA, i.e above 6000ft, as it avoids the ROD reducing below 450fpm as the flap extends, so I aim to be at 18 miles, 6000ft, Flap 1, at around 200kts.

Of course, in to an extremely strong HW I leave the aircraft clean and keep the IAS up to maintain the GS.

Working back from that I have to be at 250Kts at FL100 and have to allow about 5 miles for the decel to 200 so need to be at FL100 around 35 miles from touchdown.

Those are my "windows" in LVL CHG.

If I screw it up and lose too much energy, low and slow, I still have VS as my "get out of jail card".

There is, however, more than 1 way of skinning the proverbial and you have an array of tools available to achieve the aim which you should use according to the circumstance.

That circumstance will include adopting Rainboe's VS method when it is needed, or using the all LVL CHG method or mixing and matching.

[411A]

There is, however, more than 1 way of skinning the proverbial and you have an array of tools available to achieve the aim which you should use according to the circumstance.

That circumstance will include adopting Rainboe's VS method when it is needed, or using the all LVL CHG method or mixing and matching

Precisely.
And then there is circling to land.
Some do on a regular basis, some don't.
We're in the former category, so....that level segment at MDA is absolutely required, prior to aligning oneself with the landing runway.
And yes, we do this with a heavy widebody at 600 feet.
And at night.
And, in the rain.
The latter two cases...very carefully.:}

[Rainboe]

I find it easier to use LVL CHG and adjust the MCP SPD to control the ROD.
I don't understand this- for Boeings, LVL CHG demands idle power until the lower altitude window captures. In the meantime, MCP SPD adjusts thrust if needed to the new speed, then demands idle descent. Is this a different Airbus thing?

On a Boeing, VS is the only way if you don't want idle power descent. A CDA doesn't start on the ideal 3 degree slope. You have to adjust the ROD to reach an ideal 'window', say 10 miles 3000'. A CDA can start going downwind just a few miles from the airport. You have to set a low ROD on VS. When you are vectored base leg, you have to reassess Track miles to go and readjust ROD. The idea is to intercept GS in a steady descent and slip onto the 3 degree slope easily. I don't understand the trouble people have, but remarkably few pilots find it effortless. My strident voice demanding a satisfactory CDA and 'no level flying PLEASE!' is another problem that they have to contend with.

I think it is time for personal fines when it is not satisfactory!

[The Real Slim Shady]

The CDA in LVL CHG is simply an energy management issue: in VS if you have 240kts GS you will need 1200 fpm to stay on the 3 degree slope, but if you have a tailwind of 40kts, 200kts IAS is not sustainable in the 800W with a VS of 1200fpm unless you have a lot of drag, Flap 10.

Rainboe works for BA who don't have the 800W: his technique is no doubt effective on Classic 737s, but the FR 800Ws require a different technique as the wing is so efficient and the jet so slippery.

It is easy to generalise, but circumstances, company SOPs and the destination conspire to create many variations on the same theme.

411A, circling is a different issue as the "downwind leg" will always be a level segment.

[411A]

411A, circling is a different issue as the "downwind leg" will always be a level segment.
Absolutely correct.
And...not to be performed for those that don't know how.
Or, are prohibited from doing so, by their respective airlines procedures.

[Rainboe]

I also fly 700s! ATC don't always start you out on a CDA on an ideal 3 degree slope with free speed! You have no idea- you have to modify it as you get vectored around and get speed controlled. That theory works well when you start on a 3 degree slope? You haven't answered what you do when you are being vectored downwind with an unknown DTG. What happens when you actually have 30 track miles to go (downwind and base leg, then finals), you have no idea if you are even on a 3 degree slope, you started at 6000', and maybe you are speed controlled at 210kts as well! Try doing that in LVL CHG! You can't. The procedure you stated works well when you start out on the right slope at the right altitude and nobody cares what speed you fly! That is not how almost every LHR approach is. You must use VS- you have no other rabbit to pull out of the hat. And there is no point doing a quiet CDA if you are going to drop the gear and unnecessary flap at a higher altitude than the lowest one you can get away with. Read your ops manual! I would be surprised if you can't drop gear at 1500' on any type- even on 747, 757, and 737, that is my standard procedure. Any pilot trying to save fuel and noise should be doing that automatically now. It makes Agricola Bisporolas comments absolutely laughable in that light! I can't believe we still have people like that with such closed ears.

[The Real Slim Shady]

You don't have an "unknown" DTG; if you operate to the airfield on a regular basis you can take a best guess.

Sometimes it works, sometimes it doesn't.

As I said, every circumstance is different and clinging to a "YOU MUST ALWAYS DO IT IN VS" or "YOU MUST ALWAYS DO IT IN LVLCHG" has no validity.

We have a set of tools available to us: we must use those tools according the circumstance.

What you need at LHR, speed controlled and downwind is not the same as I need at BHX or EMA.

Dogma, however, is misplaced.

Equally, there is the Bulfer argument that VS is better as it reduces thermal shock on the engines.

Whilst I don't subscribe to that with modern jet engines (CFMs), it may have had some validity with Lycoming flat 4s.

[BOAC]

Actually the most important thing about CDAs (and circling) is to be able to do them without a load of willy-waving.:ouch:

[The Real Slim Shady]

And...not to be performed for those that don't know how.

I would add to that, or have not been trained to do it and practised it in the sim.

Circling is a very demanding manouevre and needs to be treated with caution: if you have a chance have a peek at the circling approach to Carcassonne, LFMK which we do regularly, or Derry to 08.

[The Real Slim Shady]

Actually the most important thing about CDAs (and circling) is to be able to do them without a load of willy-waving

A succinct analysis BOAC: Rainboe and his experience of LHR may be valid, but being brave enough to wave his willy universally takes big cojones ;)

[fireflybob]

I never knew such a simple procedure was so complicated!

[BOAC]

Another 'pertinence' if I may? One of the main reasons for CDAs was for noise. IF it is flown in V/S we throw away a lot of the benefit. Throttle/s closed is the ideal.

Now, some help for the buffoons who would appear to sit in the RHS of Rainboe and 411's aircraft.

Lesson 1: Know where you are in relation to the field. In the 'old days' with NDBs it was simple to get a picture (with a DME if available) of where you are. You do NOT need the FMC, range circles and the like, useful as they are. It is basic airmanship. To 'guess' at the track miles to your final gate from downwind, 20 miles from abeam + your displacement from the field, less your gate distance out is a good starting ballpark for no 'delay'. On base, 1.5 times the 'touchdown direct' distance, then subtract your 'gate' distance out..

Lesson 2: From that, you now know the 'probable' track miles to your 'gate', be it 10miles/3000' or whatever. Use V/S EARLY (if you need to) while you are at a reasonable altitude to get yourself slightly 'high' on the most probable track, so you don't have to thunder over my head at 200fpm in VS at 3500'. Saves fuel and noise.

Lesson 3: That is not easy! All sorts of things conspire against you - ATC have their own 'plan' for where you are going, departure gaps and the like. Unbelievably there are OTHER aircraft who wnat to land there too! Outrageous. So what to do? Listen to ATC and watch the TCAS and LOOK OUT OF THE WINDOW. You will soon learn to get a picture of what is likely to happen. E.G 6 ahead, 0800 in the morning, you are probably NOT going to get 'turned in early'. Revise your profile on what you have learnt.

Lesson 4: No doubt someone has given you the jet 'gates'? 30 miles or so, at 10,000' at 250 kts is pretty damn fine. Keep them updated as you get closer.

lesson 5: I was wrong - they HAVE turned me in early! No problem - drag is your friend. Learn the effect of 'early' gear, how effective the speedbrakes are, and that dropping flap does not really do much for you in the short term because you will probably (being a 'good' pilot) reduce your speed as you do, thus flattening the glide. Only later will it produce the desired effect.

Lesson 6: Learn from the previous posters - G/speed is MOST useful - if you come down at 2 or 3 times the 3 degree slope R of D you will close the profile.

Gone are the days of chopping the power at 36,000', bringing it up again at 200' and placing the jet on the numbers at Vref ('scuse the willy-waving, won't you? I haven't done a run in and break in a 737 since a trip to Volos (Greece) in 2006) but we should all try to get as close as SOPs allow.

[Rainboe]

Real Slim Shady,it won't work for 2 reasons: firstly, the min ROD is usually 450fpm
Can you post a reference to this? As far as I can gather, there is no limit figure, but a ROD of less than 200fpm is likely to be interpreted as level flight. This is the first I have heard of 450fpm!

At most places I fly, speed control is in effect during the CDA. Therefore, the only way you can do it is to assess DTG and your relationship to a 3 degree slope and 'fly it on' with VS mode. No other way works with speed control. Even without speed control, VS gives you rapid control of your general descent angle. Use LVL CHG and you will end up flying level.

[BOAC]

I do not recall any minimum 'R of D' published - only, I think, so that 'level flight' can be 'avoided', a/c should produce an altitude change of not less than 50 ft over a 2nm segment at any point. Thus R of D obviously depends on G/S.

The problem with 'over-egging' the V/S is that today's 'yoof' will come away with the idea that "Rainboe says it is ok to thunder over the environs of the airport in V/S ('as ong as V/S is >200fpm')" whereas they should all be driven to get the throttles CLOSED. As I said before, they also need to understand that V/S 200 at 6000' is a lot more 'friendly' than V/S 200 at 3500'Use LVL CHG and you will end up flying level. - but what if you use it properly?

[The Real Slim Shady]

Rainboe, The consultation document talks of 500fpm as the minimum, ergo 450 fpm or less is outside the parameter.

The whole CDA technique, however, is varied by ATC, and the reality is they don't help us: if we have a set of fixed parameters to work to it is really simple.

When they change things under the auspices of "control" it makes it trickier.

I tend towards the view that when ATC mention "control" that the CDA becomes their problem.

And as a Post Script...."Where you fly"....which validates my assertion that we have a set of tools etc.

[Rainboe]

Point taken, but the document states the limitation of minimum 500fpm ROD is specifically excluded for a CDA below Transition Level. They are giving you the option to do anything to avoid level flight with power up- that is the aim of the whole exercise, so for a CDA, the 500fpm minimum limit does not apply.

[The Real Slim Shady]

Good call Rainboe.

We have a large board in the crewroom informing us that 2.49nm level flight and min 450fpm is the requirement: someone has been telling porkies!

[BUGS/BEARINGS/BOXES]

Below the transition the VS is yours. above it 450/500fpm is the min. Or so my company's guide to CDA's states. I have to agree with the points BOAC makes. Keeping spped up/thrust low/and using "early gear" etc to slow up was an old Dan-Air method. That was, at least, till BA took over the show and some old school training capt type had heart attacks at what they were observing into LGW. :}

[Mister Geezer]

Different aircraft types will require different techniques and there are many ways to skin the cat in this instance.

I managed to become fairly comfortable with CDAs but I noticed that a number of the F/Os I flew with at my last airline were less so. Once made a Trainer, I did a little bit of research and NATS kindly supplied me with a plethora of information, including a snapshot of our performance going into LGW over a 6 month period. Some of the traces of non compliant approaches made me want to cry with people diving down and flying level from 20 odd miles :ugh: ! It was clear that a number of my colleagues had some holes in their understanding of what a CDA is and how to fly it!

However, frustrating though it was, it had to be expected since my past employer had no formal CDA training during sim or line training. This I am sure might be changing with time with other operators but I am convinced that we were not alone at the time. This is not out of neglect from the operators behalf but due to the operator not appreciating the importance of a CDA.

NATS have some really switched on guys who are responsible for CDA implementation in the UK. At the time, these chaps were getting involved with CDA implementation at foreign airfields so they are obviously specialists in their field. There is quite a bit of reading material on the net too. A quick google shall reveal all but from memory, the DfT website seemed to have the most comprehensive information available. Worth a look!

If you feel that CDA awareness and implementation could be better at your airline then get your operator to get in touch with NATS at Swanwick. They kindly offered to come and give our guys a presentation but it was sadly overlooked. The response was that we fly an older generation aircraft and a lower CDA compliance rate was inevitable! Utter twoddle, since I went though my logbook with the traces of non compliant flights and every approach I flew during that 6 month window was compliant with the CDA parameters.

[charlie83]

Sorry to digress,

I'm well aware of the CDA concept, however as "JAR" has posted from the DFT's web site, I was always under the impression that I took my rules and regs from my Part A, B, Comp Sop, UK ANO, UK AIP etc.

How do we stand with DFT publications?

Also, with regard to the 500ft (never seen 450ft) rule...

Quote

2.4 Minimum Rates of Climb and Descent
2.4.1 In order to ensure that controllers can accurately predict flight profiles to maintain standard vertical separation between
aircraft, pilots of aircraft commencing a climb or descent in accordance with an ATC Clearance should inform the controller if they
anticipate that their rate of climb or descent during the level change will be less than 500 ft per minute, or if at any time during such a
climb or descent their vertical speed is, in fact, less than 500 ft per minute.
2.4.2 This requirement applies to both the en-route phase of flight and to terminal holding above Transition Altitude.
Note: This is not a prohibition on the use of rates of climb or descent of less than 500 ft per minute where necessary to
comply with other operating requirements.



Cheers :ok:

[BOAC]

This requirement applies to both the en-route phase of flight and to terminal holding above Transition Altitude.Note:
This is not a prohibition on the use of rates of climb or descent of less than 500 ft per minute where
necessary to comply with other operating requirements

- there it is charlie83

[Pharang_Baa]

Found an ebook on Amazon to learn how to fly the CDA. Just go there and type in: How to fly a Constant Descent Angle Approach. It tells you how to use V/S.