Climb/Descent Seperation in CTA

[Dog One]

Could some of the ATC people who post on Pprune, give an insight into the wizard ways ATC control aircraft.
My query relates to operations out of non controlled airports into CTA at F180. Why is it, when faced with opposing traffic, does ATC prefer the passing to occur OCTA. Could not a reverse step climb be used to seperate the aicraft by distance ie DME or GPS? so that the passing occurs in CTA.
What lateral seperation is needed for two aircraft to pass tracking on VOR radials?
I am not on a witch hunt, but would like to understand how the crystal ball works?

[Plazbot]

1nm is the separation required laterally. Add the tracking tolerance of up to 9 degrees for no navaid plus the inbound tolerances of up to 30nm for no gear and that 1nm starts to get enormous.

For opposite direction passing, do you have a DME there or are you GPSRNAV/INS/AUSEP/ETC? What gear does the other acft have? You get zero nm with a sight and pass and to 20nm with some tricky gear. No gear, no sighting, 10 minutes after estimated time of passing. To get up before, 10 minutes prior to time of passing, nothing else.

Ground to 18000 will see anywhere from 5 to 20+ minutes before you are in need of a clearance. The other aircraft needs to descend from what ever level they are at.

When you do the numbers on just where an aircraft needs to be reference the dep/arrival aerodrome you will see that opposite direction has aircraft that are a very long way away from each other as issues.

In summary, how long is a piece of string.

[Dog One]

Thanks for the response, it would appear that the quickest and easiest way is for the outbound aircraft to climb out on a radial 10 degrees left or right of track until throough the opposite's level. Can TCAS be used in lieu of sighting and passing?

[Spodman]

Could not a reverse step climb be used to seperate the aicraft by distance ie DME or GPS?How much time maintaining FL190 on descent to facilitate separation with somebody held out at FL180 would be acceptable to you? We can only use DME/GPS when the aircraft have passed, not for any situation before they have passed.

the quickest and easiest way is for the outbound aircraft to climb out on a radial 10 degrees left or rightWell lets look at that. If you are tracking reference an NDB the tolerance is 6.9 degrees FOR EACH AIRCAFT, so 10 degrees will not work. 14 degrees won't work either, as we still need plazbot's 1 NM between the tolerances for lateral separation. The 0.2 degrees adds up to lateral separation at 294 NM from the aid.

If we take YLTN as an example this will look a bit sick with a rated coverage of 45 NM. You can't 'swap levels' on the aeroplanes the departure has left the lateral separation point, or you will need to finish it 5 minutes before the arrival enters it, and you will need to have achieved another form of separation before they leave the coverage, without introducing more complication. So departing aircraft needs to be turned 20 degrees minimum from what we expect the inbound aircraft's track to be, providing this doesn't cause a conflict with other traffic, otherwise CNARCCEAHAND. Inbound aircraft gets told to report receiving the NDB with track inbound. Until he does there is no clearance for the departure. Until the inbound is through a level the departure can climb to CNARCCEAHAND.

He departs and is told to report at 15 DME. Oh, YTLN hasn't got a DME, 15 GPS then. Oh, he hasn't got GPSRNAV, 5 minutes after we estimate he has passed 15 DME then. Hang on, that will put him around where he would be if we left them to pass in Class G airspace, then cleared the departure, and we took him off track as well...

Will he get above by 45 NM YLTN, if not what do you do? I read your post again, and note you are talking VOR, that makes it easier and you only have to turn the departure 16 degrees for the same effect, and the range is not such a problem, but no DME or GPSRNAV is still the same.

Without ATS surveillance or the flaky VFR procedures some pilots could not bring themselves to use the most efficient way to resolve these situations is that used by ATC in the USA. "Unable clearance, call again at [inconvenient time]". 'Cept we do it at FL180, them at 1200 FT AGL.

[CNARCCEAHAND - Clearance not available, remain clear class E airspace, have a nice day.]

[Nautilus Blue]

Can TCAS be used in lieu of sighting and passing?


No, there are no separation standards based on TCAS (yet!). This is another reason for doing the passing OCTA. The crews can use logic and maths to establish when they are clear of each other, we have to use Separtion Standards (allegedly devised using logic and maths but with a lot of probability and legal but-covering thrown in).

The main considerations are the climb/descent profiles and how far out the passing will happen, bearing in mind the inbound aircaft has priority.

To get up before, 10 minutes prior to time of passing, nothing else.



I think thats worth emphasising. There are NO distance (DME,GPS etc) standards for opposite direction traffic.


or the flaky VFR procedures some pilots could not bring themselves to use


I thought VFR climb was the only good thing about NAS and we lost it. Especially for the 146 out of NRV held down by an opposite direction F50 at F190 over 100nm away AND on radar.

"Clearance not available, remain OCTA"

"Request VFR climb"

"Roger climb to F240 VFR, no traffic" :ugh:

"Climb FL240" :confused:

[Wally Mk2]

It's the new year & already the MODified 'black hole' effect is in full swing with disappearing posts.:(


Wmk2

[Hempy]

The 5 mile radar standard is exactly that, 5 miles - in front, behind, to the sides, whatever. You can use radar to separate opposite direction, as long as you have vert before you lose the 5....the question is do you really want to. Off radar its 10 DME or some other sort of definite passing (opp sides of the aid etc).

[Dog One]

Thank you all for your comments.

The situation I listened to yesterday was a jet departing Kunnunnura for Broome via Gib River and Curtin. The jet departed and was told traffic was a medical PC12 inbound at F230 from Gib River. The jet was held at F180 until the PC12 passed using KU DME distances. It would appear both aircraft were IMC and no sighting and passing was possible.

The jet would have been tracking using its FMS, and the PC12 would have TSO'd GPS, so the tracking would have been accurate compared to the NDB/VOR case.

Could the controller have cleared the jet into CTA tracking offset by10nm, 20nm, or 30nm. Offset tracking is a useful feature on FMS systems, and it would appear that a clearance would easily be accomodated.

[ForkTailedDrKiller]

Offset tracking is a useful feature on FMS systems

... and on Garmin 430/530W's and I assume G1000's!

Dr :8

[Hempy]

Dog One, the offset you mention could be used to separate you, but only in certain circumstances. The scenario you mention involves climb/descent from an ad outside radar coverage. When you depart an aerodrome, you would have to track a pretty long way at 90º to your intended track to make it usefull.

My advice. If you are departing a non-controlled aerodrome and are advised of opposite direction traffic that may impede your climb profile/their descent profile, offer* to track outbound on a VOR radial that is at least 15º away from the inbound track. You will be separated from the inbound by 20 DME, can climb over him and then track direct to the next waypoint. If there is only a NDB, make the bearing ± 30º.

* offer does not constitute ATC approval.
* ATC may offer this to you anyway.

[max1]

This is where ADS-B would be a boon.

[Plazbot]

The new GPSRNAV 7v7 plus 1 separation is the shizzle. On one of the sectors I work on it has taken out nearly every single conflict except direct opposite direction (assuming everyone is GPSRNAV) without having to use navaids.

[Jabawocky]

max1.........and what would you know!!!! :ok:

Funny how some never got it :ugh:

J

[ITCZ]

Can TCAS be used in lieu of sighting and passing?
Don't do it. TCAS is not a tool for sighting and passing. Use a tool for what it was designed for.

Take a look at Eurocontrol pdf on Incorrect Use of TCAS Display (http://www.eurocontrol.int/msa/gallery/content/public/documents/ACAS_Bulletin_6_disclaimer.pdf)

Important points from that guide:
"Although the TCAS traffic display assists to detect the presence of intruders in the close vicinity, flight crews should not be over-reliant on this display"

"TCAS II bearing measurement is not very accurate. Usually, the error is no more than 5° but it could be greater than 30°. Due to these errors the target symbol on the display can jump."

Arranging your own separation OCTA is simple mental arithmetic. If you want to open a discussion on how to do that, great, look next post. Don't be lazy, don't trust the TCAS with separation OCTA.

[ITCZ]

Nautilus Blue/Plazbot/Spodman, a question -

Airway J93 GIB 071/070 KU 137nm. PC12 would have been maintaining F230 wanting descent with at least 60nm to run KU, and the Ejet airborne near KU wanting climb.

PC 12 reports established on, or N of, the KU 265ºR. Ejet reports established on or tracking to intercept KU 235ºR.

Do you give them unrestricted climb/descent to/from CTA?

The situation I listened to yesterday was a jet departing Kunnunnura for Broome via Gib River and Curtin. The jet departed and was told traffic was a medical PC12 inbound at F230 from Gib River. The jet was held at F180 until the PC12 passed using KU DME distances. It would appear both aircraft were IMC and no sighting and passing was possible.
Don't know all the facts, but I would suggest there might have been a better way to do that.

You'd be talking about the E170 and a PC12, yes? If so, a level-off at F180 is way below the optimal altitude of the E jet, which would be much better off with an unrestricted climb to F330 or higher. And though PC12 are a very flexible aircraft to operate, I'm guessing the PC12 pilot would have preferred an unrestricted descent.

The KU VOR is serviceable. My question is - why did they not arrange to track different radials?

The captain of the jet would have been the one pilot out of the three involved that (one would think) would be most interested in an unrestricted climb.

Rule of Thumb: A heading change of 15º or less will alter your ETA by less than a minute

It will also make a negligible difference to your fuel burn. Eg maximum increase of 3% for that time spent off track. Which if you do it properly, will be all over within 5 to 10 minutes. So less than 50kg extra burn due 'off track' instead of much more due to a low altitude level off.

For those that went to school, think cosine 15º = 0.97, or 3% loss of G/S or less. Exactly the same trigonometry behind 15º AoB turns in light aircraft or one engine inop turning departures in a Boeing or Airbus.

So if the Ejet and the PC12 are head to head on the KU 250ºR, why didn't the Ejet suggest: We will track to intercept the KU 235ºR, if you track to intercept or remain N of the KU 265ºR inbound, we will be separated.

At 10DME, the tracks are 5nm apart. At 30DME, 15nm apart. Easy 1:60.

I reckon if you did that, Plazbot or his mates would give an immediate clearance for the Ejet to climb.

[Hempy]

ITCZ, without reprinting the navaid separation tables ATCs use, you are essentially correct. See my reply post # #10 (http://www.pprune.org/d-g-general-aviation-questions/356504-climb-descent-seperation-cta.html#post4624702). The ±15° VOR/±30° NDB isn't a bad rule of thumb to have you clear at 20 miles.

[ITCZ]

Cheers Hempy - apologies, you did mention it before from an ATC perspective.

From a piloting perspective, 15º is optimal. Negligible difference in time or fuel to climb, or time or fuel for the trip.

Combine that with an awareness of which runway is in use, and that will be the decider for 15º 'left' or 'right' of the departure radial.

There will always be a navaid at the aerodrome for turbojet departures (CAO 82.5). Just one aircraft tracking 15º off works well with a VOR. Places like YBRM, YAYE etc only have NDB (hence V112 tracking inbound to AYE) so you need one plane to do 30º, or both agreeing to 15º.

It would be *nice* if all the other guys we shared airspace with, understood that if I/we ask for them to offset 15º, we both win.

Dog One... it is easier to do separation OCTA once you learn the tricks of the trade ;)

[Dog One]

Interesting coments (thanks everybody), similar thoughts and scenario's were discussed in our cockpit as we listened to the event.
I was surprised that ATC didn't offer the jet 15 off track to give both unrestricted climb/descent. Perhaps the controller had more than one scenario occurring else where. My FO's thoughts were for that an OCTA pass is easier to organise.

It certainly proved a good discussion point in our cockpit.

[Nautilus Blue]

The jet would have been tracking using its FMS, and the PC12 would have TSO'd GPS, so the tracking would have been accurate compared to the NDB/VOR case.



The tolerance of a VOR is 6 degrees, GPS is 7nm (it was 15 until recently) either side of track, regardless of FMS/TSO etc. As I said, these are sep standards, not logic! An aircraft tracking to/from an NDB has tighter nav tolerances than one using GPS. As an aside, that explain the NOTAM about GNSS aircfraft being still required to notify VOR, ADF etc when flightplanning).

ITCZ, yes, if time permits (standard ATC Excuse #1) and there is no other traffic in the way (standard ATC Excuse #2), diverging radials are the solution.

PC12 would have been maintaining F230 wanting descent with at least 60nm to run KU, and the Ejet airborne near KU wanting climb.


In that particular case, on normal climb/descent, would not the PC12 be below F180 prior to the Ejet reaching F180 and needing a clearance? If so, tha passing is in class G and the pilots responsbility. Whether that is a good/safe service, and what it should be is a whole other can of worms!

there might have been a better way to do that.


To be honest, quite often after a busy burst, it's possible to look back and think "I could have done that better", "If I had done this/that so and so could have had a clearance" etc. The busier you get the simpler you keep it, and unfortunately for our customers, the is nothing simpler than NO.


PS

There will always be a navaid at the aerodrome for turbojet departures (CAO 82.5).

Don't tell the guys/girls who fly 146's into Ravensthorpe that!

[ITCZ]

Navaid requirement is for night departures - oops!
it's possible to look back and think "I could have done that better",
Humbly agree - benefit of hindsight, etc.
My FO's thoughts were for that an OCTA pass is easier to organise.
I agree with your FO. But use the 15º too. Separates you OCTA, and very likely to give you the unrestricted climb/descent.

And keep up the mental arithmetic! I think the greatest part of the problem is that pilots are not taught/too easily forget the basic nav. Especially when a piece of shiny kit is in the panel.

[Dog One]

My flying these days is from ILS to ILS, SID to STAR etc, so its interesting to view the problems operating jets out of non controlled airports into CTA. Hopefully, issues raised here will be of value to the crews operating these aircraft.

Your thoughts re lack of mental arithmetic are very true. often note from the up and coming, that simple additions which can be done in the head, require the use of a calculator. They would have been hard pressed in the days of the VAN 8 Dme with no G/S indication!

[Spodman]

...why didn't the Ejet suggest: We will track to intercept the KU 235ºR, if you track to intercept or remain N of the KU 265ºR inbound,Well four things:

:8 in most cases it seems pilots don't appreciate there is another aircraft involved, when told 'clearance not available' I have many times been asked, 'why not???'

:8 Until reading this thread most pilots would not have known what our options and standards are. Finally, the PC12 would have had to ask for a clearance to wander over to the 265R, and that may not have been available.

:8 There may have been complications with having the Ejet off track further up or along the track also.

:8 I deal with a regular confliction, DHC8 departing ML for MIA conflicting with ML arrivals from the AD direction. Given the option of a 10 degree vector or lopping up to 6,000 FT off the cruise level this operator ALWAYS opts for the level. I don't know why.

Didn't have to go that far though, 265 - 235 = 30, only need 16 degrees for a 15 DME latsep point. 258/242 is enuf.

Other than that, everything that Nautilus said.:ok:

Many moons ago I ex-dev'ed a simulator exercise as a supposed 'proof of concept' of the airspace and procedures for the LAMP. Project got canned before the report was released, and I never saw it. The most fun I put in was multiple arrival/departure situations around Mildura and Mount Gambier and I designed it so a good ATC could just keep up with the traffic using diversion radials as you suggest, and the odd 'flaky VFR procedure' like VFR Climb. The proposed base of CTA was an inconvenient 7,000 FT AMSL, as against FL125 then (and now).

I then ran my guinea pig ATC through the exercises and he wasn't having a bar of this diversion radial sh!t and played overs'n'unders as you describe at KU. This changed a complex and rather busy sim run to a complete doddle. I wasn't terribly impressed, and reran it myself later to investigate how much the aircraft had been held up. I don't remember the exact answers, but it was a miniscule delay.

Perhaps Dog's controller had done the same sums and decided the result was not worth the increase in workload, or the risk. Maybe he didn't believe the pilot would actually change the track, or trust him to with no surveillance to chec? Scoff you may, but I did know a commercial pilot with not much respect for ATC who always halved vectors. If turned right 20 degrees, he would actually turn 10. He figured ATC would always ask for more than they actually needed...

And there is a risk, I am aware of one controller who did his maths badly in such a situation. He checked the inbound on the 138 radial, subtracted 16 quickly in his head, and told the other to depart on the 132 radial. The proximity of the tracks when the departure appeared on radar alarmed him, and the subsequent investigation revealed the history, and precipated a short holiday.

And :ok: to ITCZ (can I call you Inter?) as well.

[Philthy]

Arranging your own separation OCTA is simple mental arithmetic.

That may well be true in principle, but it's not quite so straightforward in practice, as a series of VERY close airproxes and near-collisions OCTA have shown. This includes in exactly the type of scenario that was the initiator for this thread. In particular, it appears that multiple conflicts and the use of multiple frequencies simultaneously (e.g. Area and CTAF) are two factors that significantly increase risk.

I deal with a regular confliction, DHC8 departing ML for MIA conflicting with ML arrivals from the AD direction. Given the option of a 10 degree vector or lopping up to 6,000 FT off the cruise level this operator ALWAYS opts for the level. I don't know why.

Yes you do! The lower GS of the turboprop means a longer vector to achieve sep. Also, the fuel burn difference for the turboprop is much less significant at the levels and on the leg lengths we're talking about. Plus jets always eventually get cleared direct to somewhere well up the track, so the diversion is insignificant for them in the overall scheme of things. That's why the Philthy Rule of Thumb was always "Go behind with the jets and underneath with the turbos"!