ATC: "Descend to ..." versus "Descend and maintain ..."

[Hardy Heinlin]

Good morning,

I've always wondered whether there is an international standard on this subject.

For example, ATC says "descend to 9000" and then remains silent for the next 5 minutes. Note that ATC only said "descend to 9000", not "descend and maintain 9000".

After 2 minutes you reach 9000 after passing a 9000B waypoint constraint. Will you continue the descent? Would you only level off if ATC said "descend and maintain 9000"?


Regards,

|-|ardy


Edit: Typo descend.

[Britjet]

It's all in the wording, which in this case is US-style.
If you are flying a STAR, you may be given a "Descend Via the XXX arrival". In this case you follow the constraints down.
Any other wording is a "hard" clearance. You don't go any lower.
For example, you may be "Cleared the XXX arrival". This, however, is not a descent clearance unless the phrase Descend Via" is used.
HTH.
Peter.

[Hardy Heinlin]

Understood. But what about the wording "descend to" alone -- if ATC didn't refer to a STAR, and you are in the vicinity of a "B" constraint just by coincidence?

Or, in other words: In which cases would ATC say "descend to [alt]"? And would this imply the suffix "... and maintain" although this suffix is not spoken?

In the CPDLC standard there are several "descend" related text blocks; two of them are "descend to" and "descend and maintain". So there must be a difference in the meaning?


|-|ardy

[simonijs]

Good morning,

Looking at ICAO Doc 4444 - Procedures for Air Navigation Services - Air Traffic Management...:

There are no examples given for the wordings "CLIMB/DESCEND TO ... and MAINTAIN". Except for when a flight is cleared to a vertical BLOCK of altitude: CLIMB (or DESCEND) TO AND MAINTAIN BLOCK (level) TO (level). All other instructions are "CLIMB (or DESCEND) TO (level). See § 12.3.1.2.

This also applies to CPDLC instructions: CLIMB (or) DESCEND TO (level). See Appendix 5, Table A5-2, Uplink message number 23.

With reference to a STAR: § 6.5.2.4 - Descent below levels specified in a STAR:
"When an arriving aircraft on a STAR is cleared to descend to a level lower than the level or the level(s) specified in a STAR, the aircraft shall follow the published vertical profile of a STAR, unless such restrictions are explicitly cancelled by ATC. Published minimum levels based on terrain clearance shall always be applied."

In such circumstances, the clearance reads: "DESCEND TO (level) [LEVEL RESTRICTION(S) (STAR designator) CANCELLED (or) LEVEL RESTRICTION(S) (STAR designator) AT (point) CANCELLED]."

I am looking into the fifteenth edition - 2007.

Kind regards,
Simon

[localiser]

To descend below the 9000B constraint on a STAR, as Peter says, I would expect to hear "descend via the XXX arrival". If that phraseology isn't used, 9000' is a clearance limit.

In any case, 9000B - ie further descent - suggests there is no terrain issue (maybe airspace) after that waypoint at 9000' so it would still be safer to maintain that level until you could get some sort of clarification from ATC.

The UK CAA RT Manual (CAP413) defines the word "descend" to mean "descend and maintain"

ICAO Annex 10 doesn't actually list a definition of the word "descend" so it's really a bit of a grey area (many of those).

[emerydc8]

Maybe Peter knows, but I seem to remember that the UK didn't follow ICAO on certain aspects of 4444. They were sticking with the way we do it in the US. For instance, if a SID had an at-or-below altitude and they cleared you to an altitude above that when you checked in with departure, you don't have to honor that at-or-below restriction.

[Hardy Heinlin]

Looking at ICAO Doc 4444 - Procedures for Air Navigation Services - Air Traffic Management...:

There are no examples given for the wordings "CLIMB/DESCEND TO ... and MAINTAIN". Except for when a flight is cleared to a vertical BLOCK of altitude: CLIMB (or DESCEND) TO AND MAINTAIN BLOCK (level) TO (level). All other instructions are "CLIMB (or DESCEND) TO (level). See § 12.3.1.2.

This also applies to CPDLC instructions: CLIMB (or) DESCEND TO (level). See Appendix 5, Table A5-2, Uplink message number 23.

[...]

I am looking into the fifteenth edition - 2007.

I'm reading the 16th edition from 2016 and there's the same: The text element "DESCENTD AND MAINTAIN" is not included. That explains it all.

It's included in the CPDLC console in PSX. I programmed this console before 2012, and I can't remember where I got these text element lists from. Maybe that element never existed and it was a mistake, or it was removed later.

Anyway, if there is just one text element of this type, there is no ambiguity at all, and my question is answered :-)


Thanks!

|-|ardy

[emerydc8]

I don't know if they ever changed this in the UK, but I was referring to this document.

http://www.ifalpa.org/downloads/Level1/Safety%20Bulletins/Air%20Traffic/11SAB01%20-%20UK%20CAA%20SID%20level%20restriction%20phraseology%20changes.pdf

[mgeiss]

On another case, if ATC wanted to clear you for a descent as published for a STAR but also include a restriction which differs from the STAR, I could imagine they would phrase it something like this (No RL ATC experience here, just Pilotedge online flying):

"Cross XXXX at 9000 then continue descent via the ABC arrival"

But I don't think I ever had a case like that.

[emerydc8]

Going into DFW on the BRDJE 3 arrival we often get "maintain 300 knots to BRDJE then comply with the arrival." BRDJE has a published speed of 280. I've heard variations to this type of clearance too, usually to American carriers who speak conversational English, probably out of expediency and because it's the fastest way to convey what they want you to do.

[tango4]

If I recall correctly the "descend and maintain" is just US phraseology, like "taxi into position and hold" instead of "line up and wait".


I totally agree with Peter on that one, every clearance is a HARD one.
It's definitely not because there are constraints written on the STAR that you should follow them, even when flying a CDA (continous descent approach). You NEED a clearance.
The only exception is the "Descend Via" which is not in use in France to the best of my knowledge.


Now, Hardy your question is not stupid as we had somes cases of pilots desending without clearance because of published contraints (but they were FLXXX or above constraints...and nevertheless some pilots thought they were cleared to that level because it was written). That is why most of these constraints (which according to me were useless and just cluttering the pilot's maps) were removed to avoid that.


Charles

[Phil Bunch]

From one of Hardy's posts:

"I'm reading the 16th edition from 2016 and there's the same: The text element "DESCENT AND MAINTAIN" is not included. That explains it all."

----------
Is it possible that confusion exists regarding the English words "descend" vs "descent"? 

Descend is a verb, while descent is a noun.   This difference might confuse text searches.  However, spoken English only provides a small difference between the sound of these two words. 

Thus, "Descend and maintain" is a proper instruction, but I don't think that "Descent and maintain" is proper textbook English.  Yet I'm sure no one would mind if either word is used by ATC (especially in a non-English-speaking country) since the meaning is clear. 

Written text in regulatory documents are a different context and textbook English would be required, I'm sure.

[Hardy Heinlin]

That was just a typo, Phil. I meant to write the verb "descend". I corrected my initial posts yesterday, but forgot to correct that one.

[United744]

Maybe Peter knows, but I seem to remember that the UK didn't follow ICAO on certain aspects of 4444. They were sticking with the way we do it in the US. For instance, if a SID had an at-or-below altitude and they cleared you to an altitude above that when you checked in with departure, you don't have to honor that at-or-below restriction.

Correct - the ATC clearance is what you fly, not what is on the departure/arrival chart.

Once ATC start to give you altitude constraints, it must be canceled before you can resume the vertical profile as per the chart.

This is one of the arguments against VNAV - it makes it too easy to bust levels/altitudes. FL CH all ATC altitude constraints.

[mark744]

This is one of the arguments against VNAV - it makes it too easy to bust levels/altitudes. FL CH all ATC altitude constraints.

In a climb, the VNAV Climb Direct ( CLM DIR ) was designed for this eventuality, clearing the constraints below the ATC cleared level in the MCP, and leaving the autopilot in VNAV  in order to comply with subsequent height and speed restrictions, without having to go to FL CH and back to VNAV.  Similarly with DES DCT

[United744]

That's true, but some still don't trust it.

The same goes for speed restrictions, too. ATC speed applies until they cancel it "SPEED RESTRICTION CANCELED [AFTER XXX]" or "RESUME OWN SPEED".

[Hardy Heinlin]

Since a waypoint speed limit is always coupled with an altitude constraint, the problem with CLB DIR and DES DIR is that you will delete waypoint speed limits too -- unless the coupled altitude constraint is outside the direct path, e.g. an "A" constraint near the ground.

[mark744]

Interesting point,
(but it wont delete the speed constraint associated with the level you've been cleared to)

So, as a matter of ATC procedure, are the speed constraints at the levels you have been cleared through still compulsory? I don't believe they are.

I would imagine that ATC are obliged to reiterate any speed requirements, as you now have a clearance that is not part of the SID or STAR you were initially cleared on. I seem to remember that if ATC don't reiterate any intervening constraint, that they are no longer valid. You should then get, as mentioned in previous posts, a clearance like -"Cross XXXX at 9000 then continue descent via the ABC arrival"

Hopefully, someone can quote the ICAO document reference to clarify.

[simonijs]

ICAO DOC 4444 is available on the internet, I just downloaded the 2016 version (16th edition). Look at Chapter 12, paragraph 3 (12.3) ATC Phraseologies, which contains "all there is". § 12.3.1.2 deals with Level changes, reports and rates. In the 2016 version, several ATC-clearances have been added compared to the 2007 version.

Regards,
Simon

[mark744]

Thanks Simon

So, simply either:
A        Climb/ Descend via XXXX SID/STAR
B        Climb/ Descend via XXXX  SID/STAR   cancel Speed/Level restriction
C        Climb/ Descend unrestricted    (cancelling all restrictions)

Not just a Climb/ Descend instruction without some form of qualification.

Makes sense