CTA base level, do you need a clearance?

[52 North]

Hi

Does a pilot need permission to enter CAS if he wishes to fly at 1.5A when flying under (or in, depending on the answer) a CTA with a base of 1.5A?

Thanks

52N

[Chilli Monster]

Yes, you do.

The base level itself is Controlled Airspace.

[ToweringCu]

You can cross the base level of an airway at 90 degrees, VMC.

[Talkdownman]

ISTR from my primary course that an aircraft may cross the base of an airway without clearance when it is defined by a flight level, and irrespective of flight conditions. If that still is the case after 40 years it should be somewhere in the AIP. Certainly not permitted if it is defined as an altitude as CM says. Perhaps Bookworm is about to confirm.........?

[vintage ATCO]

ENR 1-1-1-3

IFR:

4.1.5.1 Aircraft may, without ATC clearance, fly at right angles across the base of an en-route section of an Airway where the lower limit is defined as a Flight Level.

VMC: (Doesn't say VFR :confused:)

4.1.6.1.1 Aircraft may, without ATC clearance, fly at right angles across the base of an en-route section of an Airway where the lower limit is defined as a Flight Level.

[bookworm]

Does a pilot need permission to enter CAS if he wishes to fly at 1.5A when flying under (or in, depending on the answer) a CTA with a base of 1.5A?

Three answers to this.

1) Altitude is a continuous quantity, not a discrete one. You cannot be at 1500 ft, only above it or below it.

2) ICAO suggests that the less restrictive airspace class applies at a horizontal interface (sorry CM, no ref handy). I haven't seen a difference for the UK.

3) In practice, it's simpler to fly 100 ft below the base to avoid potential debate with ATC.

[Talkdownman]

Altitude is a continuous quantity, not a discrete one. You cannot be at 1500 ft, only above it or below it.What about a Flight Level? Is a Flight Level a 'continuous quantity' that one cannot be 'at' ?

[anotherthing]

1) Altitude is a continuous quantity, not a discrete one. You cannot be at 1500 ft, only above it or below it.

I must admit, this has thrown me ten left... how can you not be at an altitude (i.e. a specific distance above mean sea level)

Does this then mean that any separation based on aircraft at known altitudes is null and void??

I thin I understand where you are coming from but it is Mean Sea Level - otherwise how can a base of a CTA be at an altitude?

[Talkdownman]

That means we will have to dispense with vertical separation. Something less to have to remember. Hooray.

[30W]

What about a Flight Level? Is a Flight Level a 'continuous quantity' that one cannot be 'at' ?

Not if I'm trying to hand fly it it can't :(

30W

[anotherthing]

That means we will have to dispense with vertical separation. Something less to have to remember. Hooray.

Wonder if I can use this as an excuse if I have to fill in a report on STAR?!

[Talkdownman]

Do you mean to say you have time to make STAR reports?

[anotherthing]

at the moment with our watch it's aobut 1 and a half hours on console with 29 minutes off, we are a tad tight on personnel; that said you can make time if you engineer an airprox :E

[bookworm]

I must admit, this has thrown me ten left... how can you not be at an altitude (i.e. a specific distance above mean sea level)

You can't be at exactly 1500 ft any more than you can be exactly 2 metres tall. If you measure precisely enough, in any real case you will always be slightly taller or shorter than the 2 m rule, and the aircraft will always be slightly below or above 1500 ft.

You can, of course, be between 1490 and 1510 ft, or between 1499 and 1501 ft, or between 1499.9 and 1500.1 ft. If you're above 1500 ft, you're in the CTA. If you're below 1500 ft, you're below the CTA. It's meaningless to talk about the class of a plane of airspace of zero thickness.

Does this then mean that any separation based on aircraft at known altitudes is null and void??

No, because ATC aircraft separation is based on assigned altitudes or levels. When you assign an aircraft a level of 3000 ft, you can expect it to be between 2950 and 3050 ft, and you can report a level bust if it goes outside the band 2700 ft to 3300 ft. It's not going to be at exactly 3000 ft.

Because ATC assigns discrete levels, usually in 1000s of feet, it's perfectly reasonable to define separation between assigned levels.

[anotherthing]

Sorry,

did not realise we were descending into pedantry... in other words if we can use the fact that an aircraft is 'at' a level for separation then to all intents and purposes the aircraft is flying at that level; regarless of the dimensions of the aircraft... for example if the gear is down, does it's gear serve to cause a loss of separation from an aircraft below (my turn for pedantry, I know)

You are of course correct, despite your pedantry, about being exactly at a level or being exactly 2 metres tall, but for the purposes of the question that was posed at the beginning of the thread, flying 'at' 1500 QNH is good enough, in the same way as it is good enough to base separation on.

The question being if the guy was flying at, or in the vicinity of the altitude of the base of CAS.

It's a straightforward question.

[bookworm]

The question being if the guy was flying at, or in the vicinity of the altitude of the base of CAS.

It's a straightforward question.

Rephrased like that, it is a straightforward question, because if the guy is flying in the vicinity of the base but below it, no one is going to argue that he is in controlled airspace. Similarly, in the vicinity but above it, he obviously needs a clearance.

All the pilot of the uncontrolled flight needs to know is that he has to keep the altimeter needle on the correct side of the 1500 mark. He's not flying an ATC-assigned 1500 ft.

You might as well ask whether an aircraft is in controlled airspace laterally if they are on the lateral boundary. In practice, you've either stuck some part of the aircraft into the zone or you haven't.

[LXGB]

Hi
Does a pilot need permission to enter CAS if he wishes to fly at 1.5A when flying under (or in, depending on the answer) a CTA with a base of 1.5A?
Thanks
52N

Yes :)

LXGB

[bookworm]

2) ICAO suggests that the less restrictive airspace class applies at a horizontal interface (sorry CM, no ref handy). I haven't seen a difference for the UK.

I found my reference, BTW.

Annex 11 2.6
Note.— Where the ATS airspaces adjoin vertically, i.e. one above the other, flights at a common level would comply with requirements of, and be given services applicable to, the less restrictive class of airspace. In applying these criteria, Class B airspace is therefore considered less restrictive than Class A airspace; Class C airspace less restrictive than Class B airspace, etc.

Wotz that, anotherthing? "How is that consistent with your other, pedantic answer?" It's not. ;)

[anotherthing]

the joys of pedantry!!

and the joys of expecting a straightforward answer from official publications!!

Impressed by your ability (and willingness) to find these book answers :ok:

[jangler909]

Yes :)
LXGB

Don't know about UK, but in Finland flying at 1500 ft without clearance is OK.

[Ready Immediate]

I agree with jangler909. In OZ if you are at a level which is the boundary of two airspace blocks then you are in the lower class of airpace. Assuming the lower class in this example is G then no clearance required.

RI

[chevvron]

This first came up in about '75 or '76 when the LTMA base around the London area became 2500ft; we were told categorically (by the then fledgling CAA)that the base level (2500) WAS regulated airspace, hence everyone flys 100ft below it. It's best to anyway; if you fly at the base level, aircraft 500ft above the base would detect your transponder within their TCAS RA envelope.

[Turn It Off]

at the moment with our watch it's aobut 1 and a half hours on console with 29 minutes off, we are a tad tight on personnel; that said you can make time if you engineer an airprox :E

thats better than the 2hrs 1 minute on 29 mins off we get.

[anotherthing]

Turn it off

Fair point - I assume yours is a 2 hour position, whereas ours are one and a half hour positions mostly - so although we do half an hour less, it seems manpower wise we are in the same boat i.e. we are stretched to having to do the maximum most of the time.

It's all very well for SRG and the management to say a position is either a one and a half or two hour position - but have they reakised how tiring it is to do that continuously??

[Talkdownman]

if you fly at the base level, aircraft 500ft above the base would detect your transponder within their TCAS RA envelope.Our descents to 3 frequently get RA's from 2 point 4's (especially with Swiss RJ's) so some of us delay the descent in order to minimise such RAs and associated reporting nause. It has always seemed daft to me that we vertically separate consenting adults by standard separation then condone less than standard from unpredictable unknown traffic with unknown capability. 'Deemed separated', we are informed. 'Duty of Care' from the procedures planners, no doubt......:ugh:

[eyeinthesky]

Quote
so some of us delay the descent in order to minimise such RAs and associated reporting nause
Unquote

Excellent!!! that's what's known as defensive controlling' and makes sense.

Those people who give descent to 3A on top of unknown traffic outside CAS at 2.4A 'because they can' are setting themselves up for an RA or loss of separation if the guy pops up 200ft. Why risk it? Do the aircraft land any quicker?

[fireflybob]

Believe in the UK you can cross at the base level of an airway at 90 degrees if base level defined as a Flight Level.

[Talkdownman]

Keep up, Bob, keep up!

[CAP493]

Do the aircraft land any quicker?
No - but in many areas of UK terminal (controlled) airspace, because the design is so poor in respect of IAPs and the vertical dimensions of the associated CAS, this methodology can result in an approach that's not stabilised with aircraft attempting to capture the glide-path from well above. It only works well for aircraft such as the 146 series, Dash-8, Dornier 328, etc., i.e. those types where the flight-deck can adopt 'STOL' handling technique.

:8

Those people who give descent to 3A on top of unknown traffic outside CAS at 2.4A 'because they can' are setting themselves up for an RA or loss of separation if the guy pops up 200ft

Unfortunately, if the FIR traffic is wearing a conspicuity squawk, there's no guarantee that the Mode-C is correct and so the altitide of say 2400' could be totally incorrect; and in any event, it cannot be used by ATC to provided 'standard' i.e. 1000 feet vertical separation (the separation used is a 'deemed separation' against traffic outside CAS [an ICAO concept that the UK with others, adopts]) - under RAS i.e. in Class G the requirement is (I believe) 3000 feet, which would mean you actually stopping your descent at 5400 feet if the same criteria were required for traffic inside CAS against traffic outside.

Whoever said ATC is a exact science...

:hmm: