Semi-Circular/Quadrantal Rules Confusion
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Semi-Circular/Quadrantal Rules Confusion
I have my final ATC interview coming up soon and there is one area I just cant get my head round. Can somebody please clarify for me in which situations to use the semi-circular rule and the quadrantal rule and why? I have my Trevor Thom pilot books, information provided by NATS and an ATC book by Graham Duke, and these all seem to contradict each other!!
Thanks so much
James
Thanks so much
James
In the UK, IFR flights outside controlled airspace are required to adopt quadrantal level when flying above the transition altitude and below FL245. Above FL245 in uncontrolled airspace IFR flights are required to fly semi-circular levels (but try finding some of that 
).
In most other states, VFR flights are required to fly at the semicircular + 500 ft levels. The criteria for application vary, but it's typically 3000 ft amsl or 1000 ft agl, whichever is higher. This is not a requirement in the UK -- outside controlled airspace VFR flights are advised, but not required, to adopt quadrantal levels.
IFR flights in controlled airspace are required to fly at whatever level is specified in their ATC clearance. Conventionally, levels are assigned according to the semi-circular rule unless on an airway notified otherwise. Whether rules as such exist within the ATC framework to enforce that is beyond me as a mere pilot to say with certainty, but my understanding is that they do not.
).In most other states, VFR flights are required to fly at the semicircular + 500 ft levels. The criteria for application vary, but it's typically 3000 ft amsl or 1000 ft agl, whichever is higher. This is not a requirement in the UK -- outside controlled airspace VFR flights are advised, but not required, to adopt quadrantal levels.
IFR flights in controlled airspace are required to fly at whatever level is specified in their ATC clearance. Conventionally, levels are assigned according to the semi-circular rule unless on an airway notified otherwise. Whether rules as such exist within the ATC framework to enforce that is beyond me as a mere pilot
to say with certainty, but my understanding is that they do not.
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What Bookworm has said so far is spot on (as usual!
From an ATC point of view, we do tend to use the Semi-circular rule within controlled airspace in the cruise. Thus 'Westbound' flights will be at even flight levels (260/280/300/320 etc) and 'Eastbound' will be at odd flight levels (270/290/310/330 etc). Once you get above RVSM airspace (above FL410) it gets a little different, but don't worry too much about that. There also some exceptions, for example Brest Control require traffic cruising 'westbound' through ORTAC (near Alderney) to be at an ODD flight level (290/310/330 etc).
Having said all that, the traffic density and internal ATC agreements can mean that traffic actually cruises at the 'wrong' semicircular level for its direction of flight. It's not a huge problem as we have a magic thing called radar which is supposed to help us stop them from bumping into each other..
Quadrantal levels are NEVER used for a cruise level within the airways system.
From an ATC point of view, we do tend to use the Semi-circular rule within controlled airspace in the cruise. Thus 'Westbound' flights will be at even flight levels (260/280/300/320 etc) and 'Eastbound' will be at odd flight levels (270/290/310/330 etc). Once you get above RVSM airspace (above FL410) it gets a little different, but don't worry too much about that. There also some exceptions, for example Brest Control require traffic cruising 'westbound' through ORTAC (near Alderney) to be at an ODD flight level (290/310/330 etc).
Having said all that, the traffic density and internal ATC agreements can mean that traffic actually cruises at the 'wrong' semicircular level for its direction of flight. It's not a huge problem as we have a magic thing called radar which is supposed to help us stop them from bumping into each other..
Quadrantal levels are NEVER used for a cruise level within the airways system.
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Quadrantal levels are NEVER used for a cruise level within the airways system.
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More Confusion!
I too am awaiting my interviews and am not completly clear about IFR in uncontrolled airspace if not receiving an ATC service.
I understand how the quadrantal rules work when cruising, but what about when climbing or descending, surely you are travelling through levels which could conflict with someone coming the other way!
Sorry if I've missed something and this is a dumb question, but it's something that at the moment I don't quite get.
I understand how the quadrantal rules work when cruising, but what about when climbing or descending, surely you are travelling through levels which could conflict with someone coming the other way!
Sorry if I've missed something and this is a dumb question, but it's something that at the moment I don't quite get.
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I understand how the quadrantal rules work when cruising, but what about when climbing or descending, surely you are travelling through levels which could conflict with someone coming the other way!
1) Try and get a radar service
2) Try and do the climb in Visual Meteorological Conditions.
3) Cross your fingers, toes and anything else you can think of and then subject yourself to the "Big Sky" theory
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2 sheds at the confluence of control areas or airways and advisory routes. Traffic establishing or leaving Advisory Routes will be at quadrantal levels inside all sorts of Controlled Airspace. 
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Findo:
"at the confluence of control areas or airways and advisory routes. Traffic establishing or leaving Advisory Routes will be at quadrantal levels inside all sorts of Controlled Airspace."
OK, understood, but that is a transition to or from the AIRWAYS system. My original statement (with which you took issue) that "Quadrantal levels are NEVER used for a cruise level within the airways system." seems to stand, then?
"at the confluence of control areas or airways and advisory routes. Traffic establishing or leaving Advisory Routes will be at quadrantal levels inside all sorts of Controlled Airspace."
OK, understood, but that is a transition to or from the AIRWAYS system. My original statement (with which you took issue) that "Quadrantal levels are NEVER used for a cruise level within the airways system." seems to stand, then?
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In very simple terms (for the UK):
Outside CAS, you can use quadrantal rules for cruising levels below FL 245. (and you can do it VFR as well as IFR)
This provides at least 500ft separation against traffic going in a different general direction to you (but not against traffic going in broadly the same 90 deg sector as yourself). It therefore does not remove the need for a lookout!
Taking a compass rose and dividing it into quarters:
1) From 360 - 089 deg M: Odd levels (30/50/70/90/etc)
2) From 090 - 179 deg M: Odd +500 ft (35/55/75/95 etc)
3) From 180 - 269 deg M: Even levels (40/60/80/100 etc)
4) From 270 - 359 deg M: Even +500 ft (45/65/85/105 etc)
It is based upon your magnetic TRACK, not HEADING.
In Controlled airspace and above FL245 we use the semi-circular rule. This means the 500ft bits are removed and we use whole even or odd levels depending upon the magnetic direction.
As for whether you will be asked: It is a fairly basic bit of knowledge so I should think it might come up.
Outside CAS, you can use quadrantal rules for cruising levels below FL 245. (and you can do it VFR as well as IFR)
This provides at least 500ft separation against traffic going in a different general direction to you (but not against traffic going in broadly the same 90 deg sector as yourself). It therefore does not remove the need for a lookout!
Taking a compass rose and dividing it into quarters:
1) From 360 - 089 deg M: Odd levels (30/50/70/90/etc)
2) From 090 - 179 deg M: Odd +500 ft (35/55/75/95 etc)
3) From 180 - 269 deg M: Even levels (40/60/80/100 etc)
4) From 270 - 359 deg M: Even +500 ft (45/65/85/105 etc)
It is based upon your magnetic TRACK, not HEADING.
In Controlled airspace and above FL245 we use the semi-circular rule. This means the 500ft bits are removed and we use whole even or odd levels depending upon the magnetic direction.
As for whether you will be asked: It is a fairly basic bit of knowledge so I should think it might come up.
Was flying to Jersey from Cardiff (routing from Torbay) the other day, and crossed the Channel at FL50 in accordance with quadrantal rule. However was surprised to receive SVFR clearance from Jersey ATC thro Channel Is. CTR at FL60 - apparently in conflict with said rule. Didn't query clearance at time, but with hindsight, am wondering if I should have done so?
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What you were offered through Jersey was an ATC CLEARANCE. Thus they were taking on responsibility for separating you from other traffic. This overrides any quadrantal or semicircular considerations whilst you are under the constraint of that clearance.
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NATS final interview results
Well thanks for all your help guys. I have just found out that I passed the interview stage, so now am just waiting to find out when my course will be! Im really chuffed but just worried about how long it will take before I can start!
James
James
