Fly your IFR route as cleared

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Newwave
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Re: Fly your IFR route as cleared

Post by Newwave »

Nice post, i've heard many a stories about similar situations.

+1
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

cpl_atc: how do you differentiate between GPS direct and Direct?
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mattedfred
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Re: Fly your IFR route as cleared

Post by mattedfred »

thanks for the post cpl_atc

my coworkers always look at me funny when i take up an intercept heading following departure in order to intercept the direct track from the departure airport and the first fix in the clearance

the vast majority of pilots just punch in DTO the first fix as soon as they are ready to proceed enroute

i admit that sometimes the difference in track is negligible but in examples like yours the difference can be critical
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Donald
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Re: Fly your IFR route as cleared

Post by Donald »

On rwy heading after departure, center says: "Radar identified, cleared direct to..."

or

"Radar identified, cleared on course".

or

"Cleared to the XYZ airport, flight planned route".

Seems pretty simple to me.
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

Donald, I meant let's says ATC says "cleared direct XYZ"

cpl_atc said that the protected airspace is 10 nm of direct track for GPS equiped.

If I'm in my plane, with no GPS and in range from XYZ, my protected airspace is supposed to be much bigger. As said in earlier post, ATC doesn't seem to read your equipment code, so they don't know you don't have GPS, are they automatically give you 10 NM because they "assume" you're GPS equipped? I've been cleared direct from 150 nm before on a TACAN and yes, I bet I was more than 10 NM from the actual direct track.
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Donald
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Re: Fly your IFR route as cleared

Post by Donald »

AuxBatOn wrote:I meant let's says ATC says "cleared direct XYZ"
Hit the DTO button and go.
AuxBatOn wrote:If I'm in my plane, with no GPS
Tell ATC, we are unable direct, requesting vectors or on course FPR.
AuxBatOn wrote:I've been cleared direct from 150 nm before on a TACAN and yes, I bet I was more than 10 NM from the actual direct track.
If you accept the clearance, you better be able to do it. If not, tell them "unable".
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

Donald, I'll explain a few things...

first, I can't hit DTO Enter

Second, yes you are able direct, you receive the station (didn't I tell you we were in range?) So I can accept.

Third, direct implies great circle on ATC screens. Well, we work in Magnetic in the airplane. 150 NM away, the magnetic variation is different that the mag var where I am. The TACAN emits radials, in degree magnetic from where the station is. My kit (any kit), translates that into a steering to take with the magnetic variation where you are. So, I fly a steering to the station that is 3-4 degrees off (150 NM away that's about 10 NM off the track ATC expects us to fly), even though I fly an accurate track to the station. As I get closer, I can actually see the track to take changing. Now, we have an INS which is NOT IFR certified but that is dead accurate. If I punch in the coordinates of the TACAN station, I can actually see, 150 NM away, that the station representation on my digital map is 10-20 miles off to the south of the station. It happens on any aircraft, people just don't realize it because they don't have a depiction of where the kit thinks the station is.. This is WHY the protected airspace on conventional DIRECT is larger...
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FamilyGuy
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Re: Fly your IFR route as cleared

Post by FamilyGuy »

Don't forget in this debate the "protected airspace" in a RADAR environment is only 5 or even 3nm!

It doesn't matter if the pilot "thinks" ATC is watching our every move and basing sep on that - sometimes they actually expect you to go either PP direct or ON COURSE. Sometimes they do watch your every move - sometimes they DON'T! At those spacing intervals there is very little room for error.
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

FG, on a conventionnal equipped aircraft off airways, this is impossible to achieve. I seriously doubt it's 5NM especially when a VOR AIRWAY is what, 4 NM protected airspace initially then 4.5 degrees? Doesn'T make any sense that a PP Direct is less than that...
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FamilyGuy
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Re: Fly your IFR route as cleared

Post by FamilyGuy »

Sorry my bad. Conventional or /S won't be cleared PP direct - unless the navaid is close. Most controllers I know "allow" for /S if it's tight...ie. assigned headings.

The post was aimed more at the boys with the fancy gear that think it's okay to go PP direct as opposed to "on course".

If in doubt check it out....or If in doubt chicken out.
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

FG, just for my own info, how big is the protected airspace around a PP DCT with conventionnal navaid?
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Bookem Lou
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Re: Fly your IFR route as cleared

Post by Bookem Lou »

AuxBatOn, i may be mistaken here as I have never flown for the military or used a TACAN. If you are flying a straight line (direct) to a station, whether it is VOR or TACAN, your track and bearing will change over the course of the flight (while correcting for local variation unless you are slaved to a flux gate) yet it will be the shortest, most direct route to the station. If you are using GPS, your track and bearing will change as well. Otherwise you would be flying rhumb lines to everyplace you go. They may appear as curved lines on the map but they will be straight in relation to the real earth. Take a flight coming from Europe going to pretty much anyplace in North America. Their track initially will be a northerly heading, changing to westerly and eventually south as they pass the pole. They would be flying a straight line. If you could receive a VOR in NA from that sort of range, it would be a northerly radial but your heading away from Europe would still keep you on a northerly heading. The only time your track and bearing will not change is if you heading straight magnetic north or south, and more or less west or east along the equator with respect to the isogonic lines. If you are navigating with respect to true north, it becomes even easier.

Unless I've missed what you are saying, this is correct. I've used GPS and INS, LORAN, the good ol VOR and NDB and it has been the same in every case. I can't see the Tacan being any different. The only question I have is do you have a track bar or a needle indicating you are on or off course?
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

The TACAN isn't any different than the VOR. Just mechanic instead of electronic. I was looking at my map display and the station was shown a good 20 miles to the south of the actual position of the station. Obviously, as we got closer, the error got smaller and smaller. But aiming directly at the station on my kit would most definately bring me somewhat off track (I figuerd 10-15 miles again, on that map display). I guess that's the same reason why when you change over stations on airways, you're not dead on airway center in relation to the other NAVAID.

AuxBatOn
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Bookem Lou
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Re: Fly your IFR route as cleared

Post by Bookem Lou »

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.
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Pygmie
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Re: Fly your IFR route as cleared

Post by Pygmie »

Bookem Lou wrote: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.)
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

Spacing is okay, what I'm asking is tolerance each side of the cleared route.
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Pygmie
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Re: Fly your IFR route as cleared

Post by 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.
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by 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?
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zzjayca
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Re: Fly your IFR route as cleared

Post by zzjayca »

AuxBatOn wrote: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.
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

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

Cheers
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zzjayca
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Re: Fly your IFR route as cleared

Post by 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.
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by 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...
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Pygmie
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Re: Fly your IFR route as cleared

Post by Pygmie »

AuxBatOn wrote: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.
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Pygmie
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Re: Fly your IFR route as cleared

Post by Pygmie »

AuxBatOn wrote: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?
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AuxBatOn
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Re: Fly your IFR route as cleared

Post by AuxBatOn »

Not RVSM. We use VOLUT/C.
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