Fly your IFR route as cleared

[Pygmie]

Just one last thing I want to point out. The reason that there is bigger spacing between aircraft using conventional navaids like VOR and NDB is that the conventional navaids are less accurate than GPS, not because there is ambiguity as to where the aircraft (or the station) is. When you figure GPS is precise to within 10 feet and a VOR on its own can't place you guaranteed within 1 mile over better than 100 miles more than 50% of the time. The slight movement of your HSI track bar could be hundreds or thousands of feet of lateral movement the further you get, a significant amount when we're placing aircraft within 5 miles of each other on occasion.

Actually, domestically, the spacing between aircraft using conventional navaids is much less then the required separation for aircraft using GPS direct tracks. (Non-radar separation, that is. On radar 5 miles is 5 miles, regardless of what the aircraft are navigating with.)

[AuxBatOn]

Spacing is okay, what I'm asking is tolerance each side of the cleared route.

[Pygmie]

Well, if you want to go into specifics. . .

The protected airspace (tolerance + separation + error factor) air traffic control uses for an aircraft operating between two conventional navaids is: 4 miles (4.34 miles if NDB) either side of the centerline to a distance of 51 miles (50 if NDB), then expanding outward within lines that diverge at 4.5 degrees (5 if NDB) until meeting similar lines from the next navaid.

The protected airspace (tolerance + separation + error factor) for GPS directs (and RNAV directs within adequate signal coverage) is 10 miles either side of the centerline.

Again, this is all for NON RADAR separation. On radar, 5 miles (or 3 in certain places) between targets is the separation standard.

[AuxBatOn]

Thanks, but I knew for the airways. I was wondering off airways. But I guess on Radar it doesn't make a difference from what I understand? You need to maintain 5NM so if you clear me direct YQT for example, you'll keep an eye on me and that would be the end?

[zzjayca]

Thanks, but I knew for the airways. I was wondering off airways. But I guess on Radar it doesn't make a difference from what I understand? You need to maintain 5NM so if you clear me direct YQT for example, you'll keep an eye on me and that would be the end?

Direct point to point using standard equipment, (/S on the flight plan) outside of signal coverge of a navaid or while not on an airway, your protected airspace is 45nM either side of track.

This is only non-radar. If you are within radar and frequency coverage (controllers must have direct controller pilot communication to use radar standards) then we only protect 5nM regardless of the equipment onboard the aircraft since we are using our equipment (radar) rather than position reports from the pilot/aircraft to determine separation.

[AuxBatOn]

Thanks for the answer. So if I go too far off track because of the issues mentionned before, you'll tell me!

Cheers

[zzjayca]

Exactly. In fact, if you are /S and are not yet in range of for example YQT, we should be giving you a heading to fly until you are able direct on your own. If we don't, just ask for one.

[AuxBatOn]

Yup, and that's what I usually do. I was just wondering once I get cleared direct what happened on your side.

On an other note, do you guys read the equipment code before clearing someone direct? I have been cleared NUMEROUS times direct from 300 nm away from a station and everytime, as you said, I would come back "Unable direct request initial vector"? We are not S (we do not have ADFs), but we are VOLUT. Maybe the fact that we usually cruise into or above RVSM makes controllers think we are RNAV equiped...

[Pygmie]

Thanks, but I knew for the airways. I was wondering off airways. But I guess on Radar it doesn't make a difference from what I understand? You need to maintain 5NM so if you clear me direct YQT for example, you'll keep an eye on me and that would be the end?

Exactly right, we'll keep an eye on you on radar and if you start getting too close to other traffic, we'll put you on a heading to ensure an accurate track until after the traffic is clear.

And it doesn't matter if there is an airway there or not, the numbers I mentioned above can be used any time an aircraft is navigating to or from a navaid. So if you are given PP direct a navaid, those numbers still apply.

[Pygmie]

On an other note, do you guys read the equipment code before clearing someone direct? I have been cleared NUMEROUS times direct from 300 nm away from a station and everytime, as you said, I would come back "Unable direct request initial vector"? We are not S (we do not have ADFs), but we are VOLUT. Maybe the fact that we usually cruise into or above RVSM makes controllers think we are RNAV equiped...

Which equipment suffixes do you file as, and are you RVSM certified?

[AuxBatOn]

Not RVSM. We use VOLUT/C.

[Steve Baker]

I find it suprizing that the protected airspace, non-radar on a VHF/LF airway is less than on a GPS direct, at least until over 100 miles away from the nearest navaid. I just went through RNP 4 groundschool and the end result of that training seemed to imply that the centreline of two parallel airways would be 5 x the RNP of the airspace. WATRS airspace has recently dropped to RNP 10 and plans to go RNP 4 soon. We were told that this was the highest nav performance requirement of any oceanic airspace. Now I know that oceanic is not the same as domestic non-radar but, it would seem to me that over long non-radar airways the same seperation challenges would aply and that the protected airspace of something as inaccurate as VOR/NDB would be a little greater.

Of course the above is a hijack, the original post was absolutely correct and there is no excuse for pilots not complying with the clearance as read back.

[it'sme]

Sort of along the same lines but from the other side of the mike:

File a flight plan that includes the following routing.... direct xxx intersection, direct yyy vor direct destination zzz. Receive the IFR clearence prior to departure that includes the routing as was filed......program same into FMS,,,,depart, contact departure and given turn to such and such heading intercept airway so and so to yyy vor.

Now in the overall scheme of things we are going to be fairly close to the flight planned and initially cleared routing but not exactly as now cleared. This now requires heads down while the FMS is reprogrammed by one crew member and verified by the other to exactly match the new cleared routing at a phase of flight where a fair bit can be going on in the cockpit never mind keeping a set of mark one eyeballs outside.

The point I am getting at is if the flight planned route isn't going to work for the departure folks then don't give it to us in the clearence at the outset. We would much rather be doing route programming on the ground with the park brake set rather than 2,500 ft in the climb.

Yes, before I get flamed, we have other toys in the cockpit that we can immediatly use to identify and track the new routing but that's not the issue.

We have had this exact scenario now four times in the last 90 days and twice in the last two weeks, all from the same departure airport.

[the_professor]

The point I am getting at is if the flight planned route isn't going to work for the departure folks then don't give it to us in the clearence at the outset. We would much rather be doing route programming on the ground with the park brake set rather than 2,500 ft in the climb.

I sympathize with your logic, and it is totally reasonable.

However if the clearance is being delivered by a tower ("Cleared to XXX via the Blah Five Departure, Flight Planned Route, squawk 0456"), the tower has no idea (nor are they expected to) of the dynamics of the sky at any given moment, in terms of if the flight planned route will "work" for the flight in question. Unless otherwise advised by the Centre controller, the tower will clear the flight as per their flight planned route. Sometimes the Centre controller knows before the flight becomes airborne that they will need to change the route (or offer a different route to the pilot), but issuing the change then requires a relay through the tower (which requires a readback), etc... Due to the nature of tower operations it is sometimes either impractical or impossible to revise a particular flight's route prior to wheels-up. And sometimes the Centre controller needs to consult with the pilot before making a final decision.

It is far easier to do some of this when speaking directly to the crew, as opposed to relaying through another controller.

A crew should obviously never jeopardize the safety of the flight for something like programming a route change into the FMS. If you're too busy, then don't acknowledge the transmission, or ask for an initial vector until you get the route change programmed.

Don't forget that route changes mean extra work for the controller(s) as well, and they're not initiated for no reason.

If you find that the controllers for a particular departure location routinely initiate route changes at inappropriate times, I would recommend contacting the Shift Manager at the ACC in question for further discussion.