Continuous Descent Approaches

[fireflybob]

More and more airports now expect CDAs.

Given that you have FMS what advice/method do you employ to ensure a CDA on every occasion, flight safety permitting?

Thanks for any suggestions.

[Intruder]

Make sure you know how to program YOUR FMS for the best performance! For example, if you know your FMS does not program speeds well during this type of descent, use manual override so the FMS can concentrate on the vertical path. If its VNAV is weak under those conditions, use V/S. If it works well using full VNAV, use it that way!

[Human Factor]

My trick:

Ensure that the route in the FMC is a good approximation of what you're expecting. Look at the landing time on the FMC. Look at current altitude. Work out appropriate constant rate of descent.

Works every time.;)

[haughtney1]

Spot on Rainboe....:ok:
I am amazed at the number of pilots who apparently make no effort and happily level off at 3000' in early morning arrivals or lates.
I'm amazed that it tends to be the older "wizer" heads that seem to level off first;)

[fireflybob]

Thanks for the replies, guys.

Personally I enjoy the challenge of flying a CDA, very satisfying when it works out right!

[parabellum]

"I'm amazed that it tends to be the older "wizer" heads that seem to level off first;)"

Is that because you are the only one still awake at that time Haughtney?;)

Once in the descent the FMC is for guidance only, theory to be backed up by practical experience of that particular approach, my 2cents, FWIW.

[Dream Land]

Can work out fine if ATC is interfering with your descent, just leaving it managed works fine and lasts a long time if ATC cooperates.

[BOAC]

Perhaps time to remind all that there is NO minimum rate of descent for a CDA. If you need 300fpm, do it.

[haughtney1]

Perhaps time to remind all that there is NO minimum rate of descent for a CDA. If you need 300fpm, do it
As soon as I get that base leg or final vector.....I us the V/S I want, as has also been stated, you get better with a bit of practise...as witnessed today by my Capt who remarked how good my effort was:E
(all I need now is to get the right result:p )

[BOAC]

...................and a bit less of the older heads if you don't mind :)

[BOAC]

I think any 'level' portion lines you up for the guillotine.

[sickBocks]

Constant Descent approach busted if ATC spot any level segment of>3nm below 6000ft.
[Why we can't fly idle at 330kts to 10nm, level and then close the thrust levers I don't know as that is quieter than -200ft/min just to tick the box :p maybe it's the extra noise generated by the subsequent go-around]

[Telstar]

Can anyone point me in the direction of any official documents about CDA?

I find myself under increasing pressure from the company to observe these things as is everyone but for example I never heard it mentioned that you are allowed a 3nm level segment or a descent rate of 300 fpm. Where can I read the rules and regs?

[BOAC]

Your company should provide this. There is no 'allowance' for a 3 ml level segment!! That is what will trigger a non-compliant approach. There should be a minimum level segment in the TMA.

Try continuous descent approach in Google - that will fill your day:)

It is now virtually a world-wide procedure.

This may help (http://www.britishairways.com/travel/crnoise/public/en_gb). I cannot instantly see the reference to 'any rate of descent' but in my experience there is no minimum in the TMA where CDA are 'required'.

[Telstar]

League tables are published and we get letters if we don't comply but I have not seen any information on techniques or the rules of the game published. Which is disappointing as one of the big two of operators in STN.

[Earthmover]

There is in fact a publication in the UK that covers this: "Noise from Arriving Aircraft" published by NATS, BAA and others, which is primarily aimed at LHR, LGW and STN (but not RW05)

It does, on page 8, mention a 2.5NM level segment to decelerate (therefore the assumption is that thrust is at flight idle) before the descent commences. Furthermore there are very good tables on page 15 which give you V/S and FPA versus distance and altitude. These tables also mention the level segment - but assume 20secs of level flight at 210KIAS - one can only assume that the 2.5NM previously stated is a maximum (ICAO requires a minimum of 1.5NM)

I'm with Rainboe on the FMS/FMC/FMGC. On my type, it will schedule the next flap manoeuvring speed before you've wound 'em out which could be a tad embarrasing if you get distracted!

[skiesfull]

Why so little regard for CDAs? Because for many 'book' pilots, it is too difficult to do, if they cannot programme the FMC to do it for them! Too many have been told not to use VS because it does not include 'speed protection' and therefore will not use it, and the view of central London is better from 3-4000ft than it is from 5500ft!

[haughtney1]

Well said Rainboe.....its easy enough to muliply your G/S by 5 to get a required ROD for 3%, then the rest is just the 3 in 1 rule plus a bit to slow down:ok:

[OBK!]

Doesn't happen all the time obviously because of ATC vectors away from the mental path you may have. The 300ft/mile is a good basic rule but for most aircraft I find this requires a "power on" descent given the majority of jet aircraft can descend around 1000ft every 3 miles on idle power.
I swear by gates. 8000ft/250kts downwind, 1200ft/min gets it slowing down and going down gently without having to use power to arrest descent. Gets a bit twitchy at times (especially in the bus with the well known balloon when selecting flap 2!) But like with majority of companies, ours doesn't offer any advice/practice on CDAs and therefore those gates mentioned above often scare the guy in the left seat. Not sure if this is because they don't have faith in me or prefer to keep it straight forward.

[haughtney1]

The 300ft/mile is a good basic rule but for most aircraft I find this requires a "power on" descent given the majority of jet aircraft can descend around 1000ft every 3 miles on idle power.


I guess just not the jets I fly:ok: 300ft/mile usually equates to 5 X the groundspeed:}

[OBK!]

But lets say you're at 220kts...you'd want 1100fpm for 300ft/nm descent. Idle power, in the A320 will typically give around 1300fpm-1500fpm (apologies if you're already well aware!) Admit it's not much power though to reduce by 200fpm-400fpm.

Not sure about other bus drivers but I find the vertical management is pretty useless below 10,000ft when wanting to achieve a CDA, given it programmes a level flight portion to slow down. Some work mates swear by it though and prefer to get down to about 4000ft and choose V/S 300fpm in the last 1000ft before G/S intercept....does this doesn't qualify as a CDA?

[Anotherflapoperator]

I must get it right about 4/5 of the time I fly into LGW- twice a day. However, though we have very primitive nav kit, we do have a copy of the booklet LGW sent us with the tables in. That certainly helps, as does the ability of the 146 to steepen it's descent if you get it wrong.:p

I often have to fly about 2-300fpm to stay sensible, but If I've got the ones that allow it, I can set up a couple of mythical base leg and long final points and give them a vertical gate to help- that's with a GNS-XLS as well, not a fancy modern FMS. Just using every tool in the box to help.

Obviously an FMS based approach would help, but sometimes you get silly long downwind legs to alter spacing for departures that bugger up any hope of getting it right. Not our fault but does that affect the published stats?

[Fredairstair]

Nice thread.

I think at LGW, the normal min ROD (500fpm) doesn't apply below 6000'(?)

Also it seems there are two flavours of controllers at LGW, the good and the excellent. With the good ones you have to watch your track miles v.closely and dust off your 3x table. With the latter, just do as you're told and it works beautifully. The problem is of course, you don't know which flavour you've got until it's too late!!!

I find that the G/S indicator on the standby horizon "wakes up" before the one on the PFD/ND, this can help with your VSing to keep the CDA going.

[loubylou]

Er - not mythical if you're flying into Manchester - it's in the UK AIP to descend at min rate of 500ft per min.
CDA's are done at there 2200-0700 though.
However - you are quite right for Gatwick - it says that the pilot decides the best rate of descent required to achieve continuous descent:)

louby

[BOAC]

it's in the UK AIP to descend at min 500ft per min - which takes me back to post #17 - I KNOW I was told (by BA) there was no descent rate limit in the the TMA for CDA, but I CANNOT find an official reference to it. Does anyone have one?

Think I crossed there with your edit, louby - are you saying that IS in the AIP?

[loubylou]

Each airfield has their own procedures - you can look up the relevant airfield on the AIP web site, I just had a look! www.ais.com

louby

[loubylou]

ARGH crossed again!!!
Yes ! Go to the txt bit for the appropriate airfield and it will be in there:p
louby

[BOAC]

That should be ais.org.uk (http://www.ais.org.uk/aes/login.jsp).

...and there it is,

AD 2-EGKK-1-18 para 5.a

..........and what is a chap to do?

AD 2-EGCC-1-15 2.d and e.2

...whereas Stansted says nothing.

Sounds as if the airfields need to sort this out. Any ATC comment?

[loubylou]

Thanks BOAC - I got booted as I realised that - and I thought having broadband meant never getting booted :{

Anyway - hope that helped you find the reference you were looking for

louby

[BOAC]

....we must stop crossing like this:)

[loubylou]

:p

louby

[Fredairstair]

Rainboe, you've got me there - I can't find a reference that specifies a minimum rate of descent (I'll get back to you!) However......

ICAO 8168 1.4.1.7

min rate of descent for Cat C/D/E in the final approach segment is 590 ft/min.

UK AIP AD-2 EGKK 1-15

"....a descent will have deemed to have been continuous provided that no segment of level flight longer than 2.5nm occurs below 6000' qnh and level flight is interpreted as any segment of flight having a height change of not more than 50' over a track distance of 2nm or more"

UK AIP AD-2 EGKK-1-18

"on receipt of a descent clearance the pilot will descend at a rate he judges will be best suited to the achievement of a continuous descent, the object being to join the glide path at the appropriate height for the distance without recourse to level flight"

This is fun isn't it?

Fred.

[ElNino]

From the UK AIP:
2.2 Minimum Rates of Climb and Descent
2.2.1 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.
2.2.2 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.
My reading of this is that flying at less than 500fpm is not prohibited, as long as you have informed ATC. The requirement to inform ATC is removed when flying below Trans Alt, as per 2.2.2. Therefore my conclusion is that one is perfectly entitled to fly at less than 500fpm below the Trans Alt whenever it is required. The "Note" in 2.2.2 would seem to reinforce this, as a CDA is certainly an "operating requirement" at some airports.

I have also come across a document called "Noise from Arriving Aircraft - An Industry Code of Practice", dated Sept 2001, which has the following line:

35. The instructions in the UK AIP that referred to a minimum descent rate of 500 fpm
are to be clarified, enabling extended descents in line with CDA to be achieved
without need to notify ATC of lower rate of descent below transition altitude. This
will come into effect from 4 October 2001.
I think note 2.2.2 from the AIP is this clarification. Admittedly it's not overly clear that it is applying to CDA's, but I think a literal reading of it allows for less than 500fpm when required.

[Fredairstair]

Well played Sir!

Now why couldn't I find that........:confused:

[BOAC]

but below Transition Level, CDA takes over. - re-read post #34. 500fpm MINIMUM applies at EGCC for CDA approaches and, I think, at EGSS. The 'Code of Practice' has not yet been fully implemented.

[haughtney1]

re-read post #34. 500fpm MINIMUM applies at EGCC for CDA approaches and, I think, at EGSS. The 'Code of Practice' has not yet been fully implemented.
Today 11:44


So I'm gonna get a bollocking for doing 400fpm to splodge the G/S and MCP alt..rather than flying level for a bit?
Throw in a tailwind in the wrong place...and a bit of anti ice, and this rule seems to be bloody idiotic:ugh:

[BOAC]

I don't thinks so - I don't:) . I'm just pointing out the 'letter of the law' regarding descent rates.
PS a tailwind will help you.:cool: