Continuous Descent Approach

[Dream Land]

I would like to hear some opinions of a technique I am seeing cadets use that is driving me crazy, we will arrive into our STAR free terminal area and we are being vectored / sequenced depending on current traffic, so a typical situation is receiving a descent from say 9000 FT to 5000 FT initially the pilot selects Open Des then intervenes at say 7000 with V/S - 1000, then when arriving at 6000 FT reduces to V/S - 500, then within 200 ft of the altitude then again reduces to V/S -200. :ugh:

I asked the pilot what he was trying to accomplish and he told me he was trying to make a smoother descent.

In our terminal area, they tend to stick to non radar separation event though they use radar, so quite often by the time we approach our assigned altitude, we again receive another descent, even though in the 321 you can barely hear the engines, but, I am listening to every spool up and spool down, observing EPR jump up and down each and every time the pilot plays with the V/S knob, my question is, who is teaching this stuff and how can this possibly save any money.

Thanks in advance for replies, D.L.:ok:

[Ndicho Moja]

It would suggest an incomplete understanding of what they are trying to achieve, not to mention a waste of fuel.

[PantLoad]

Dream Land,

I would suggest you point out to the training department AIM section 4-4-9 "Adherence to Clearance".

Fly safe,

PantLoad

[de facto]

Isnt a CDA mainly for noise abatement purporse?
Leveling off will increase the noise and fuel consumption especially with flaps extended.
Therefore your "CADET" is in the good direction.
Using idle thrust(ie lvl chg) when given in this post a 4000 ft descent, is a poor technique,it will increase your fuel flow as you will level off too early and the noise will increase,potentially ending in a fine for noise infringement.

Id rather fly with him in england(cda is monitered) than with someone who has no idea of this basic concept.

Just got the definition of a CDA by Euro Control:“Continuous Descent Approach is an aircraft operating technique in which an
arriving aircraft descends from an optimal position with minimum thrust and avoids
level flight to the extent permitted by the safe operation of the aircraft and
compliance with published procedures and ATC instructions.”

The operational aim :The overall operational aim for a CDA is to assist pilots to optimise aircraft approach
profiles in order to reduce noise impact on the ground and, where possible, reduce
fuel-use and atmospheric emissions. Because noise reduces exponentially with distance
between source and receptor, the main aim of CDA is to keep aircraft as high as
possible for as long as possible without adversely affecting the application of a safe
descent profile. Additional noise reduction may be achieved by incorporating, to the
extent possible, LP/LD techniques such as later deployment of flaps and undercarriage.

Safe and efficient flights to all of you:)

[BOAC]

DL - it rather sounds as if your 'cadet' is not familiar with the CDA principle as DF says - and you do not say where this 'operation' is taking place, but perhaps a quick reminder to 'lad/ladess' of the 3 x tables and suggest starting at 1000fpm if not 'pushed' for height while he/she does the maths and then arranging r of d to suit desired vertical profile once 'high/low' etc has been mentally (or magenta line if they must !!) computed?

[Centaurus]

Direct your cadets to fly it manually instead of playing Atari sets with knobs and buttons. I guarantee they wouldn't have a clue how to fly. This is automation dependancy at its worst.

[HEATHROW DIRECTOR]

<<Also could somebody confirm (for example in London TMA) when ATC considers an aircraft to not having performed a CDA... I'm pretty sure you are allowed to fly level for a while (2-3miles??) before there is a trigger of non CDA compliance.. >>

I retired a while back but, so far as I know, ATC is not concerned whether a pilot flies the CDA as long as he complies with ATC instructions. (Because of other traffic it's often not possible to fly CDAs anyway) However, the airport authority has some means of determining whether aircraft have flown CDAs. What action they can take I do not know.

[Upper Air]

Why don`t you just brief him/her about how you want the profile achieved. . ? Using selected speed (or not) distance and height.

x3

[de facto]

Alpagueur,

what i meant is if one is below of a continious descent profile(optimum of course being idle thrust) and dives at idle thrust to end up leveling off time after time during vectoring is poor practice.
In best of case,atc will advise you the track miles(i recall STN) or if uou ask kindly:-) then uou can do the altitude/distance rule and get a good V/S.

I see no problem to do 500ft/min the last 3000 feet to avoid leveling off for 10 miles there after.

Of course level off to decelerate from clean speed to flaps speed is ok as long as you judge well...much easier to descent 500ft/min and catch the glide while decelerating to your flaps speed,less noise bust possible.

Heathrow director,The airport via the noise sensors will send a fine to the company in question...
Same when you dont monitor your track precisely or t/o noise procedure.the trickiest i remember being london stansted,where the 3000ft acceleration use to coincide with the first hard altitude in the step climb as the 90 degree left turn would start,so bank 30 minimum clean speed would just do it on our 737,faster and you would overshoot the turn or slower(flaps 1 speed) and you would level off with plenty of drag and get noise fine...

[sevenstrokeroll]

bravo BOAC.

[kotakota]

Any self-respecting driver should be pleased to use CDA as a part of his/her skills. I was very pleased when it was introduced at both London airports . The satisfaction of a well managed approach without flying level .
I am amazed how freakish I seem to the locals on my fleet in the sandpit when I try to teach them how to manage distance to go vs height etc - the airline cannot be bothered with teaching any skills or airmanship to the cadets. Just the basics , might as well disconnect V/S , just as they might as well disconnect the indicators on their Porsches as they do not seem to need them or even know how to operate them .But then again , they cannot fly a visual approach or circuit , a circling approach is an abomination to them !

[Genghis the Engineer]

CDAs as also provide significant fuel saving - a trial at EMA (http://www.atmseminarus.org/seminarContent/seminar7/presentations/pr_119_EC.pdf) a few years back saved about 73 per approach on MD11ss and about 30kg on B757s. But they were designed for the noise saving advantages, and do work for that.

Flown properly it should ideally be at constant descent rate until levelling to intercept the glidepath. Of course, that assumes that local geography and airspace allow this, which it seldom does.

Easing off the descent rate on the way down is missing the point completely - the rate should be as constant as permitted all the way from cruise altitude to levelling to intercept the glideslope.

And as others have said - fly the clearance or challenge it!

G

[sevenstrokeroll]

while it is old advice...a long , idle , descent can lead to a surprise if you need the engines ...so, check them , by revving them up a bit, at least by 3000'. Indeed, it was our policy to NOT be unspooled down low.

altitude to lose

times 3nm per thousand feet = distance to lose altitude

5 times ground speed equals rate of descent in feet per minute to make good above.

but, because NO one knows how the winds will change as you descend, start down 10 miles before the above equation...and in this way you will be able to gradually level off for a smooth ride...otherwise the descent level off will break your neck (kidding).

so...lose 10,000 feet

u need 30 nm

400 knots ground speed means 2000 fpm

so start down 40 miles prior to crossing fix and adjust rate of descent as ground speed changes

good luck

[411A]

...it was our policy to NOT be unspooled down low.


Superb advice, especially on older types (new(er) as well...:ok:

Sometimes...pointing the nose down (way down) makes for a expedited descent.
IE; been known to happen.:D

[Prober]

Oh dear oh dear! One can see automation becoming the god here. There are so many ways of killing the cat and it really is up to the pilot to choose the best use of modes etc depending on the tactical situation at any one given time. He could even - heaven forfend - dispense with the automation and use his "skills". 30 odd years ago, on the Gripper, it was the norm to try to set a given power at ToD and not touch the "throttles" until touchdown going into LHR. Of course it required a good knowledge of the usual procedures and the expected miles to run but, as I am sure Heathrow Director will acknowledge, Approach controllers, especially Director, were absolutely top notch and one could see their intentions a mile off (well, make that a hundred!).
Prober

[SidHolding]

In my VC10 I will often fly a CDA so that I am well prepared if it is required, eg at Hannover or Edinburgh.

My rules of thumb are to be at 6000 feet with 20 nm to touchdown, providing I am on speed (210 kts). It will normally be idle power down to about 2500 - 3000 feet, then increase the power to counter the drag changes during configuration, the power will vary depending on weight/temp/wind etc, to stabalise at approach speed (170 kts). Obviously, in the VC10 I have no advanced automation, so the whole thing is judged mentally and constantly reviewed.

[galaxy flyer]

SID

You are among the Few of your age that can fly an airplane, as opposed to play a video game. Lots of "pilots" now know nothing of figuring descents, having some basic "milestones" on descent and decceleration, power settings that will work thru configuration changes. It's all a mystery to the video gamers. I brief these things in a automated bizjet and the young ones look at me like Grandpa.

Wait 'til all the power goes out!

GF

I learnt all the techniques and tricks instructing on the C-5

[non0]

V/NAV is probably better solution (both for fuel consumption and noise abatement) and use V/S only if you are above the VNAV PATH glide.

[Slasher]

I learnt all the techniques and tricks instructing on the C-5

Same here but as a FO on the 727, before the days of
computer games and FMCs.

Provided the box is loaded correctly and you're aware of
your weight and prevailing w/c, the A320/1 Frogmobile
gives a handy DTG readout at the bottom of the F-PLN. I
use it quite a lot esp when on oblique radar headings etc
on descent. The kids are usually glued to the Progress and
yelling if the box thinks I'm too high or low. That 'c' (the
hypotenuse) is of a shorter distance than 'a' + 'b' seems
to escape or confuse them.

[de facto]

Oh dear oh dear! One can see automation becoming the god here

We just use the resources given to us.

You are among the Few of your age that can fly an airplane, as opposed to play a video game. Lots of "pilots" now know nothing of figuring descents, having some basic "milestones" on descent and decceleration, power settings that will work thru configuration changes

Maybe because no one showed them or let them do their own descent profile to learn by their own mistakes....
Help them and show them...that will be useful no?

The kids are usually glued to the Progress and
yelling if the box thinks I'm too high or low

kids....:cool:

[fireflybob]

Is there something new in this CDA thingy then?

Circa 30 years ago it was a matter of professional pride to close the thrust levers at top of descent (F330 or more) and not be spooling up until 3 or 4 miles from touchdown - and, by the way, this was hand flown with distance to touchdown being mentally calculated using VOR/DME (barrel type) and/or ADF.

With all the gizmos available now people seem to make such a song and a dance about it - KISS!

[de facto]

Maybe 30 years there werent so many restrictions,less traffic...most airports where a continious idle descent is possible are those which airspace isnt overcrowded...
Handflown with idle thrust aint a real challenge,or was it 30 years ago?:E

[fireflybob]

Maybe 30 years there werent so many restrictions,less traffic...most airports where a continious idle descent is possible are those which airspace isnt overcrowded...

There were still plenty of restrictions then - descents these days more continuous from an atc perspective due one way routings and radar cover - little has changed when it comes to execution of a cda from that point of view

Handflown with idle thrust aint a real challenge,or was it 30 years ago?

Agree but we didn't have fmcs and magenta lines - there seems to be an obsession with putting every macro change into the fmc instead of thinking about what you're doing!

[Greenpilots]

Oh boy...

I am one of the computer gamers, but I will give you a perfect CDA anytime, provided I have any information about track miles. That has nothing to do with hand-flying or computers, but is simple math. Loose 3000' per 10 miles and calculate about 4-5 miles for a 50 knot speed reduction and you can't go wrong. Throw in some experience on your aircraft (sub-type, weight) and ATC to make it perfect. Add/subtract another few miles (FEW!) to your initial descent point for wind and you are in a perfect position for idle power till glide path intercept...

LHR is one of the airports where this works really well, although not on idle power... CDA required below 6000', however the minimum descent rate may be less than the UK norm of 500'/min. CDA is given, if a descent of 50' in 4 miles (might be 5 or 6 even) is done and that is not really hard to achieve... The technique used in the first post makes me wonder, why I plan for a CDA approach every single time...
One of my instructors once said that one should rather go for the challenge and if you are bit high, you can always use a speed brake...

PS: The Airbus calculates its decent in a very conservative way, so being up to 500'-1000' high on its calculated profile (PROGRESS page on MCDU) will most propably still give you a stable approach.