Descent Clearance Question

[numbo jumbo]

Hi All

My understanding is that whilst on a given STAR with a level restriction, any subsequent descent clearance below the restriction negates the crossing level or "gate". I'm unable to find anything in the CAP 413 but would appreciate any feedback on what the official take is on this.

For example a STAR - Abbot 1C into STN gives a LAPRA crossing at FL 120. If a subsequent ATC clearance is to descend to FL 110, does this remove the LAPRA restriction?

Thanks.

[TypeIV]

Minimum enroute/obstacle clearence/arrival's published limitations must be obeyed even if you are cleared lower, unless vectored. You usually get cleared to execute a certain STAR and together with that a clearence to descend. The STAR also includes those restrictions.

Many controllers use the phrase "open descent/no altitude restrictions", depending on where you are together with the clearence to cancel those restrictions.

[Tom!]

In my understanding, in your case the restriction still applies, because you are still on the STAR routing. If you are given a direct to ABBOT the controller should include it in his clearance. (eg, direct ABBOT descend FL90, abeam LAPRA FL120 or below.)

Of course I could be wrong, standing by to be corrected.

[BOBBLEHAT]

Any further clearance negates the previous.

It is written somewhere can't remember where. You may get lot's of people (probably other ATCOs) tell you that we still expect you to make the previous level restriction etc etc, all that may be so but the basics are that a reclearance becomes the only clearance you are working to. It has to be that way when you think about it.

If you are coming into Abbot via LAPRA and are cleared below FL120 and the controller still wants FL120 @ LAPRA than it must be "descend FLxxx, cross LAPRA 120 or below" or something like "descend FLxxx previous level restriction applies"

[despegue]

Bobblehat is correct.
Any new clearance by ATC negates a previous clearance.

[Crazy Voyager]

From CAP493
When an amendment is made to a clearance the new clearance shall be read in fullto the pilot and shall automatically cancel any previous clearance. Controllers must be aware, therefore, that if the original clearance included a restriction, e.g. “cross ABC FL150 or below” then the issue of a revised clearance automatically cancels the earlier restriction, unless it is reiterated with the revised clearance.

sec 1 chap 4 page 4, para 7

[Dan Winterland]

''Bobblehat is correct. Any new clearance by ATC negates a previous clearance.''

Not everywhere - in some countries you are still expected to adhere to the published constraints. For example, Hong Kong. You won't know this unless you've checked the AIP - so be careful. It's best to ask.

[despegue]

You are obviously right Dan!
Indeed always check with ATC when in doubt. thank you.

[de facto]

A level restriction on a STAR is there for a reason,so if you are cleared to a lower level(in the Abbot 1 C),planning to cross the published waypoint at the correct altitude is proper airmanship.
If the restriction is fuel consumming,by all means confirm or request cancellation of the restriction by ATC rather than playing with the controller words and ignore a restriction that could lead to serious problems in a busy environment.
And yes reading the AIP is always a good idea when operating into new airports.

[despegue]

Problem is that not many airlines have the AIP available for operating crews. AIP availability is also still limited via the net, and often only available when paying.

[numbo jumbo]

CAP 493

Thanks Crazy Voyager and all respondents

I've just looked in CAP 493 where it's states the answer clearly. It removes any ambiguity and I will carry a copy of this with me from now on.

ATB