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LB777

Question about ATC clearances

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Hello all

 

I wanted to ask the atc pros out there about altitude and speed constraints that you often see on charts, namely: can these get overruled by an atc clearance?

 

Let me give you an example, let's say I'm on this STAR (LUSAR 1N)kaC5Bl0.png

 

And I'm somewhere near LUSAR at FL220, if the controller clears me directly to 5000 ft, does that mean I can bypass the altitude constraints on the chart?

Same for speed, if he says "free speed", I assume you can go up to 250kts under 10000ft and whatever speed above 10k?

 

Finally is it the same for SIDs? Someone told me that there were some differences between STARs and SIDs in this regard.

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Yes, all these (SIDs/STARs) can be overruled by ATC. However the controller would(should) never issue a clearance that would put you in harm way relative to terrain.


Michael J.

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It depends on where you are. In some countries, such as the US, the descent clearance will delete the restrictions while in other countries, the pilot will still be expected to adhere to the restrictions.

Yes, all these (SIDs/STARs) can be overruled by ATC. However the controller would(should) never issue a clearance that would put you in harm way relative to terrain.

That is not necessarily true that the contrillers would not put you in harm's way. There are countries where the controller will grant altitude requests that will place the aircraft below mva.

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As mentioned above, it depends where you are.

 

SIDs -- in the UK the phraseology is "climb now" (as in "BAW123, climb now FL140"). This means the SID level constraints are cancelled and you should climb directly to the cleared level.

 

The ICAO equivalent phraseology is "climb unrestricted". If you don't hear either of the above, you should comply with the level constraints (though it may be worth querying as in my experience the controller almost always intends for you to climb direct).

 

On a STAR, again, in general unless the level restrictions are explicitly cancelled you should still abide by them. The exceptions are in the UK where all the levels published on STAR charts are advisory only (if you look closely at the charts you'll see notes to the effect that the levels are for descent planning purposes only and actual descent clearance is by ATC), and the USA, where a descent clearance overrides the chart unless you cleared to "descend via the XXX arrival" -- which means you must comply with the constraints.


Simon Kelsey

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Once cleared to a fix, it usually deletes the other constraints.  However, some countries have published speed limits outside of the SIDs.  One example is Mexico where it is 250 kts below 10,000 AGL.  In some areas you will have to start slowing around 16000 MSL.  Watch your flap MACH limit!


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Thanks everyone really interesting stuff! Especially in the UK, I never knew the levels on STAR charts were only for planning purposes, good to know.

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No worries.

 

To answer your question about speeds -- again, in the UK (and most of Europe to my knowledge) the phrase "No ATC speed restriction" means that in most circumstances (in the UK, inside Class A/B/C/D airspace -- elsewhere, class A/B/C) you can fly any speed you want -- including above 250kts below FL100 (most airlines like high speed below FL100 as it is money saving -- a very few have SOPs in place prohibiting >250kts below FL100 unless ATC specifically asks for high speed, but those cases are company rules, not legislation). If you're in class E/F/G (in the UK) or D/E/F/G (elsewhere) the 250kt below FL100 speed restriction still applies.

 

That said, even "no ATC speed restriction" does not override speed limits published on a SID or STAR -- the reason being those speed limits have been designed in to the procedure for a reason and if you try and blast around the corner at SOVAD (in your example) at 300kts the resulting increased turn radius is likely to take you outside the protected airspace or closer to an obstacle than you might like! Likewise, on a SID you are still responsible for maintaining the correct lateral track for obstacle or noise preferential route reasons and therefore to remain within the protected track you'll need to comply with the charted speed restrictions.

 

Finally, on an airmanship note, just because ATC removes the speed restriction doesn't mean that you should go barrelling towards the final approach at >300KIAS even in the absence of charted restrictions -- it's still up to the pilot to slow down and configure!

 

In the USA and Canada, controllers are not authorised to lift the 250kts below 10,000ft restriction and so you must always comply with that (and the SID/STAR charts, for the reasons mentioned above) even if you're given 'no ATC speed restriction'.


Simon Kelsey

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