ROD during a CDA

[squawkident.]

Hello,

I'm wondering what the min VS rate is accepted by ATC in London, to comply with a CDA.

I know the AIP mentions min level change of 500fpm in UK airspace but I recall reading somewhere 300fpm about a CDA but I can't find that reference anywhere.

In other words, if I 'glide' it under the glideslope at 200fpm, is that acceptable both by the noise CDA standard and by ATC?

Thank you

SIdent.

[FlightDetent]

IIRC the 500 min standard does not apply for CDA below TL.

i.e. YES (not an ATC here).

[Talkdownman]

Heathrow CDA is (was?) based on 300ft/nm. Driver (or plane...) works out the ROD depending on IAS. Intermediate app from Min Stack FL flown at min clean (around 210-225KIAS), Base Leg at 180KIAS. We would count the track miles to the runway and pass it to the driver on descent. We might fib a bit depending on who we were telling to achieve desired result. There'd usually be a couple of miles level flight before G/S intercept for gear and flaps etc. There's probably an 'App' for it all now...'Heathrow App App'...

[DaveReidUK]

From the Heathrow AIP:

"For monitoring purposes, a descent will be deemed to have been continous provided that no segment of level flight longer than 2.5 nautical miles (nm) occurs below 6000 ft QNH and 'level flight' is interpreted as any segment of flight having a height change of not more than 50 ft over a track distance of 2 nm or more, as recorded in the airport Noise and track-keeping system"

Nothing about a minimum ROD.

[FlightDetent]

NATS Safety Notice EXT 02/2008. Page 2 here http://www.ukfsc.co.uk/files/FOCUS%20-%20Past%20Issues/Focus%2072.pdf

[DaveReidUK]

NATS Safety Notice EXT 02/2008. Page 2 here http://www.ukfsc.co.uk/files/FOCUS%20-%20Past%20Issues/Focus%2072.pdf

If I understand that document correctly, it says that ATC will expect a minimum ROD of 500 fpm unless they are advised otherwise.

It doesn't seem to have any bearing on what ROD is or isn't considered to qualify as a CDA.

[FlightDetent]

Heathrow CDA is (was?) based on 300ft/nm.
the 500 min standard does not apply for CDA below TL.
This requirement applies to both the en-route phase of flight and to terminal holding above Transition Altitude.CDA = without recourse to level flight 'level flight' is interpreted as any segment of flight having a height change of not more than 50 ft over a track distance of 2 nm or more

Looks like we have all we need, or am I missing something?

[DaveReidUK]

Looks like we have all we need, or am I missing something?

Except that we haven't actually answered the OP's question (which admittedly was confusingly phrased):

I'm wondering what the min VS rate is accepted by ATC in London, to comply with a CDA.

I'm still unclear what connection the OP is trying to make between a minimum rate acceptable to ATC, and CDA compliance.

Anyway, looking at a random sample of aircraft currently being vectored from the LHR holds to the 27L/27R ILS, RODs are considerably greater than the quoted 300 fpm.

[FlightDetent]

There is no ATC restriction on how small your V/S may be. That's how I read the AIP and NATS leaflet. Even if less than 500 ft/min, no need to tell them.

ATC will arrange so that 300 ft / NM - AKA little less than 3° - is a possible trajectory. That is around 1000 ft with 220 kts after leaving the holding facility, or 800 ft/min later when slowed down to 180 kts.

My experience is to use that V/S to get down below glidepath, thus enable for swift deceleration from altitude below the profile when asked to reduce to 160 kts, and 210 to 180 without staying too high.

OP's 200 fpm in that latter stage is perfectly acceptable to ATC and complies with CDA low noise profile requirements. To satisfy, both level flight of less than 2 NM, and V/S at least 100 fpm are prescribed. There is no "at least" ATC restricion on V/S, however doing less than 100 ft/min may invalidate CDA. 100 ft/min exactly would be good enough up to 240 kt groundspeed.

Essentially, we are surely thinking the same, sorry for being tightlipped before.

Simple version: Use any V/S as long as you keep descending, but make sure you avoid flying level for more than 2 NM.

[DaveReidUK]

ATC will arrange so that 300 ft / NM - AKA little less than 3° - is a possible trajectory.

Ah right, I didn't read Talkdownman's post carefully enough.

Then again, he doesn't pay any attention to mine, so I don't feel too guilty. :O

[chevvron]

Ah right, I didn't read Talkdownman's post carefully enough.

Then again, he doesn't pay any attention to mine, so I don't feel too guilty. :O

Oi it's my job to wind up TDM not yours.

[squawkident.]

Thx very much guys and gals.

Ok, so above FL70 for LGW, min 500 fpm.
Below FL70, ATC don't mind the ROD but must be greater than 100fpm, to satisfy the level segment 2.5miles.

TY

[OhNoCB]

I'm still unclear what connection the OP is trying to make between a minimum rate acceptable to ATC, and CDA compliance.


I would guess that it comes from wanting to know if they are doing something technically wrong by using very very low rates of descent in order to make a 'CDA'. One airline I worked for was quite bad for doing this, and would descend fairly promptly to make sure they didn't leave themselves high but would then use 100fpm descent approaching the cleared altitude to avoid 'leveling off'/getting ALT HLD, this way it is still a CDA. Sometimes this is the only way to do it whenever you get given more track miles than expected but generally I find it against the spirit of things and try to use 500fpm, but it is useful to know what is technically defined as OK - which by this thread appears to be whatever you want below TL.

[FlightDetent]

Agreed. I try to fly CDAs eveywhere, with a target speed of 700 fpm. That is not compatible with ATC speed control. So 1000/500 where there are bigger fish to fry.

Should less than 300 be needed, I give myself a D.