CTA base level, do you need a clearance?
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CTA base level, do you need a clearance?
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
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
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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.........?
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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
)
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.
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
)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.
Originally Posted by 52 North
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?
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.
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Originally Posted by bookworm
Altitude is a continuous quantity, not a discrete one. You cannot be at 1500 ft, only above it or below it.
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1) Altitude is a continuous quantity, not a discrete one. You cannot be at 1500 ft, only above it or below it.
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?
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That means we will have to dispense with vertical separation. Something less to have to remember. Hooray.
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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 
Originally Posted by anotherthing
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, 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??
Because ATC assigns discrete levels, usually in 1000s of feet, it's perfectly reasonable to define separation between assigned levels.
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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.
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.
Originally Posted by anotherthing
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.
It's a straightforward question.
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.
Originally Posted by 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
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
LXGB
Originally Posted by 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.
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.
