Class D - Metro vs Regional

[ian00798]

If 8500 is the LL, then that is the last level outside controlled airspace. ATC would issue aircraft at 9000ft giving a 500ft buffer to OCTA.

This is correct, as per AIP ENR1.4 1.1.7

 

The class c steps around airports are designed based on the aircraft types that use them and their climb/descent profiles. Generally, most aircraft on a normal climb or descent won't even get to within 2000ft of the actual lowest level. If the LL is 850o and the airspace below is class g, then at 8500 class G services apply. I quite often see VFR aircraft under the Tamworth 8500ft step at 8500ft, and they are treated as though they are in class g airspace. Sometimes IFR aircraft get given traffic information on these aircraft.

 

Regardless of this, as per the AIP you must remain outside controlled airspace or request a clearance. If you are going at 8500ft under CTA, you want to make sure you are watching your altitude pretty carefully to avoid a VCA. Probably easy to do in normal cruise on a calm day, not so easy if in a high workload phase on a bumpy day.

 

 

 

[facthunter]

If an aircraft cleared for and flying in controlled airspace can fly at the lower level and still remain in the CTA, how can you fly at the same level and NOT be in the CTA? The aircraft may have received a clearance like "xzy descend to 4,000 when ready, report approaching or when visual" Where high terrain is involved the required safe altitude above it may require a CTA step that is higher than what it would be over flat country so to have a good even descent profile the descending aircraft may run right onto the level of the step legally. If you are operating on the correct frequency for being OCTA, you won't be aware of the other traffic. Don't forget altimeter variations also. Everyone at that stage will be operating on an area QNH but some will be updated and there is an allowable error in a TSO'd altimeter also. I have suggested 200' as a buffer, but there is an argument for allowing more. Nev

 

 

[rhysmcc]

If you are flying at the lower level you are OCTA, regardless of how you got to that level (from below or above with a clearance to leave controlled airspace).

 

To me it doesn't make sense flying along at 8200 or 8300 to give a bigger buffer with those flying at 9000 because you've gone and reduced the buffer to those whom may be flying IFR at 8000 OCTA.

 

 

[ben87r]

We were told during training that all planned CTA climb/descent profiles had to be no less than 500' above the steps. Not sure if it is something that has changed over the years tho.

 

 

[facthunter]

It's certainly wise to ensure there is clearance. Nev

 

 

[frank marriott]

 

We were told during training that all planned CTA climb/descent profiles had to be no less than 500' above the steps. Not sure if it is something that has changed over the years tho.

That is in the VFG also Ben, I had 1000' in my head for some reason until I was corrected above.

 

 

[ian00798]

An aircraft that is flying at the lower level will not be flying in controlled airspace, as per the AIP reference that I listed above. I have also attached a copy of the manual of air traffic services regarding this to this post. An aircraft can not legally run right down to the level of the step legally, IFR aircraft must remain not less than 500ft above the lowest level published on the chart. If you are going within 500ft of the step, you should request a clearance to leave and reenter controlled airspace.

 

Consider the Tamworth airspace which I have attached a photo of to this message. Say you want to depart Tamworth at 6500ft to the south. When you get to 23 dme Tamworth, you would have your control services terminated by Tamworth tower and have a frequency transfer approved. At this point the correct frequency to be on would be 124.8, the class g airspace frequency. The lowest level that ATC could assign an aircraft to remain in controlled airspace in this step is 7000ft.

 

There may be some variations in altimeters, but the whole reason behind VFR altimeters having to be accurate to within 100ft before flight is that if two aircraft both have their altimeters out by 100ft, you should still miss each other by 300ft, or 100m. I don't believe adding 200ft buffers is wise, and you are required to maintain hemispherically compliant levels above 5000ft. Adding 200ft buffers just puts you close to other aircraft, all of a sudden you may be within 150ft of an IFR aircraft flying below you in G. BEN87R, what your instructor told you is correct and as per the AIP.

 

 

 

 

[facthunter]

I never said I would cruise at the 200 ft allowance. All I said was I wouldn't climb to closer than that. and it's a special situation over high terrain with timber so gliding capability is important. I distinctly recall an advice that "un notified traffic may be at the lower levels of the CTA"..... so don't go to that height. When you are climbing or descending you can't obey quadrantal or hemispherical levels obviously. Nev

 

 

[rhysmcc]

Controlled traffic (CTA) can't be operating at the lower level, because the lower level is uncontrolled airspace (OCTA). If they are descending through the lower level, then they have been cleared to leave controlled airspace, normal class G radio (see and avoid) comes into place, ATC will give traffic on known or observed traffic but at 8500ft both aircraft are now OCTA.

 

what do you do after climibing to within 200ft of the lower limit if it's not considered cruising?

 

 

[facthunter]

Descend fairly soon after. Don't always make it to that level but it's a self imposed limit. Its a unique situation there with densely wooded steep hills. I consider it tiger country.

 

Surely the lower limit is a boundary. That's how it's defined. When you descend through it you are not in CTA. How can you leave it before that time? Nev

 

 

[rhysmcc]

8500 is OCTA, 8501 is controlled, controlled aircraft flying at 9000 that wish to descend further are Cleared to leave controlled airspace. ATC are not required to separate aircraft in controlled airspace with those aircraft operating OCTA, traffic would be provided as best as possible. Both aircraft should be on the area Freq.

 

not sure if that's what you were asking?

 

 

[facthunter]

You are telling me a lot of things I haven't asked, and they are not relevent to my concerns. I don't see it getting anywhere. Nev

 

 

[rhysmcc]

Well what is it you are asking?

 

 

[facthunter]

Forget it. If you have read everything carefully that I have posted you would have it.. People have lost interest..Nev

 

 

[Pearo]

Descend fairly soon after. Don't always make it to that level but it's a self imposed limit. Its a unique situation there with densely wooded steep hills. I consider it tiger country.Surely the lower limit is a boundary. That's how it's defined. When you descend through it you are not in CTA. How can you leave it before that time? Nev

Just say the CTA step is 4500. I assume ATC will not clear you to fly at any lower than 5000, or most likely 5500 for us VFR folk. The only time you will be cleared to descend below 5000 is if you are leaving CTA, and in that case I have always been asked to report passing 4500 (which at that time ATC will approve frequency change). Our awesome ATC mates on the air usually give a report on VFR traffic in Class G below if they have radar coverage.

 

In the aforementioned case, I can descend from 5500 (with ATC permission only of course) to 4500 where I will be approved for a frequency change.

 

I have done this at YRED before. Descend from Brisbane CTA to the 1500LL at YRED which is the overfly height for the aerodrome.

 

 

[facthunter]

I ran this in front of a friend of mine a week ago, who apart from starting flying with the army in PNG worked in Airlines and as a CASA FOI for quite a time, and he said if an aircraft is in CTA and descends to the lower limit, at the time of reaching the lower limit it leaves CTA. Until that point it hasn't. (I'm not talking about getting clearances or changing radio frequencies, which is a separate issue.). I said I had been maintaining a min of 200' buffer at the boundary he said "why not" and that it was a prudent idea and a good safety concept. Nev

 

 

[rhysmcc]

That's great but puts you 200ft closer to possible IFR cruising the opposite way. Why not stick to the levels recommended.

 

 

[facthunter]

Just flying levels doesn't guarantee no contact, even above 5000. where it's required not just recommended. Don't forget this is high terrain area where you try to extend glide capability. I'm not advocating cruising at that level. Climbing and descending aircraft aren't separated as they aren't maintaining a level by definition and are OCTA not position reporting or within radar range.

 

People flying in CTA have positive controlled separation from other aircraft in CTA. They are OK but all others are not. They have to rely mainly on eyes with some help from others who use radio (properly). Nev.

 

 

[rhysmcc]

I said I had been maintaining a min of 200' buffer at the boundary he said "why not" and that it was a prudent idea and a good safety concept. Nev

So are you cruising at a non standard level or not?

 

 

[facthunter]

No. The level is a limit not a height maintained. This has been gone through before. Plenty of flights have no real cruise phase if they are a short sector. Why would you level off at a lower height when you could climb higher and have a better glide capacity, if you lose the engine.? It's some of Australia's roughest terrain.Nev

 

 

[rhysmcc]

I guess we have different understandings of cruise.

 

Climb to a limit, sometime later maybe climb some more to another limit...a while later descend to land. Personally I'd call the limits cruise.

 

Why would you level off? Because CTA is above you.

 

 

[facthunter]

Perhaps if you examine the terrain and the overlaying CTA , it would make more sense. The ground isn't far below even when you are about 5,000 feet. The best thing if you had the performance would be to get a clearance into the Controlled airspace, but it might not be for more than 5-10 minutes at most, so hardly worth it. It's not a regular track but there are a lot of powered chutes about just south to keep an eye on. I tend to fly to and over clear(er) patches so dog leg, while the fearless go direct. Nev

 

 

[kaz3g]

I seem to remember that ATC allow up to a 200' deviation from assigned altitude? Something that can be extremely difficult to do in the Auster in summer thermals.

 

Kaz

 

 

[rhysmcc]

200ft is the tolerance from your transponder altitude return

 

 

[Pearo]

200ft is the tolerance from your transponder altitude return

Occasionally when its really busy in the circuit at YRED, sometimes I find I might have busted the Brisbane CTA by maybe 100ft or so. When I realise I very quickly push the nose down! At what point will you normally issue a VCA?