Cutting Corners at VORs

[Flylo]

When flying towards a VOR in order to intercept an airway, or a radial, that you are going to fly outbound on, and the new radial is within say... 100 degrees... of the radial you are flying inbound on; how close do you have to get to the VOR before you can cut the corner under IFR? Or do you have to cross the VOR at all times before heading outbound.

My instructor, "Full Flaps" Flannagan, gave me an answer but I can't find it in print.

Thanks for any input.

.

 

[Kream926]

fly to the vor, get a from indication, finger out what radial your on and how far off from the one you want, double the deflection till intercept


ex. flying inbound on 180 raidial and you want the 330 out bound

fly over vor, get a from, you should then be on the 360 which is 30 degrees off, double it for a 60 degree intecept heading then shallow out as needle centers


hope this helps

 

[cvsfly]

What did your instructor tell you? He should tell you to look it up from an official source, not here. Start studying the AIM. To make it easy, try 5-3-5. Waiting for station passage may be OK in a 100 kt ground speed trainor, but not in a faster aircraft or strong tail wind.

 

[minitour]

I don't like that "double the degrees off on Sunday after three in IMCon odd days..." (you get the idea) stuff. I like to make itsimple...

Cross it and turn to an intercept heading.

You know before you get there what radial you need, right? So just turn for a 30-45 degree intercept heading.

ex. Heading inbound on the 270 radial (090 heading) and you needto pick up the 133 radial. When you go from TO to FROM turn rightto about a 165 heading. Flip your OBS to 133 and you'reset...when the needle centers up, join it.

If you're in a windy situation, you'll know that before you get there to turn.

Say you've got winds out of the south so your actual compass heading is105 inbound on the 270 radial. You are correcting how manydegrees to the right? 15. So add 15 to the 30 or 45 degreeintercept that you would have turned to.

Personally, I like 30 degree turns. Even PTs, I'd rather do a tear drop than a 45/180, but that's just me...

The only time I've used 45 degrees was flying inbound on the (justusing numbers) 180, I had to pick up the 240 outbound. I turned45 degrees and picked it up a little quicker...

FWIW, the same thing works for NDBs

Hope it helps.

-mini

 

[pireps]

Check out AIM chapter 5-3-5. It talks about relation of aircraft speed and course changes. This might be what you're looking for. The jist of it is, the faster you are, the more likely you are to bust the airway (4nm from centerline) when making turns for course changes. Probably not an issue for small GA aircraft, but definitely something to think about. Passing over the station and then turning is not necessarily the best technique.

 

[pireps]

Wow, two people beat me to it while I was typing!

 

[minitour]

Check out AIM chapter 5-3-5. It talks about relation ofaircraft speed and course changes. This might be what you're lookingfor. The jist of it is, the faster you are, the more likely you are tobust the airway (4nm from centerline) when making turns for coursechanges. Probably not an issue for small GA aircraft, but definitelysomething to think about. Passing over the station and then turning isnot necessarily the best technique.

True, and I agree, but unless you've got DME or some other source ofinformation, how do you know when you're close enough to the VOR?

Obviously in bigger, faster stuff that would require a turn before thestation, you're most likely going to have that equipment, but in a 172,sometimes all you've got is 91.205 (excluding the DME above 240) andoccasionally you're lucky enough to get two OBS displays...yummy...

-mini

 

[cvsfly]

True, and I agree, but unless you've got DME or some other source ofinformation, how do you know when you're close enough to the VOR?

Obviously in bigger, faster stuff that would require a turn before thestation, you're most likely going to have that equipment, but in a 172,sometimes all you've got is 91.205 (excluding the DME above 240) andoccasionally you're lucky enough to get two OBS displays...yummy...

-mini

Practice and experience will tell you where you are in relation to the VOR. (needle sensitivity) Fly headings, don't chase needles. Good situational awareness and dead reckoning. Reliable and tested equipment help too. This figuring out intercept angles after station passage is fine in the training world and you probably won't exceed airway dimensions or get a call from ATC wondering if your missed your turn, but in the commercial world your expected to anticipate and be situationally aware. Keep practicing those intercepts as you are taught and you will eventually be able to anticipate the timing and degree of intercept on your own in varying wind conditions and do smoothly.

 

[A Squared]

The AIM seems to suggest that there is no protection beyond the standard airway width. That is not true. Below 10,000 ft, at a VOR you aren't afforded much extra, if any, but above that to 18,000 feet, you are protected in a curve 8 NM beyond the VOR (10 NM secondary protection) and above 18,000 ft the primary area is extended 13 nm past the VOR and 15 NM for the secondary area.

Now, assuming a 90 degree turn in an airway (anyone know of an airway with a 90 degree turn?) how close do you get? Your ground track is a function of your groundspeed, and roughly speaking, a 90 degree turn at standard rate takes 100'th of your ground speed in nautical miles, i.e. a 150 tooling along at 100 knots with a 50 knot tail wind will take 1.5 nm to turn 90 degrees. That makes 2.5 more miles before you approach the edge of the primary area. Remember, this is a turn of 90 degrees. More likely, the turns you encounter are going to be 45 degrees or less, which keeps you much closer to the centerline. SO, if you're smoking along at 9000 ft in a King air at 240 knots toward a 90 degree turn at a VOR, you might want to start your turn early. If you're bopping along in a 172 toward a 20 degree bend in an airway, you have quite a bit of room to complete the turn. That is not to say that you shouldn't turn promptly as soon as you identify station passage, but that worrying about leading the turn is unnecessary.

 

[PropsForward]

Don't forget that if it is that big of a turn, just ask ATC to fly to the next fix/vor, they usually will accomodate especially if you are within 10 miles of the VOR your making the turn at.

 

[UGAflyer]

just turn when the 430 or 530 tells you to...

 

[avbug]

Start your turn a mile and a half or so early most of the time, you'll be fine. If you don't have DME, then you should be timing your progress. You'll not the CDI getting more sensitive.

If you have absolutely no idea where you are, then wait for station passage or for the needle to begin getting erratic as you approach the cone of confusion, and make your turn. Then do something to ensure that you're not so lost next time. You should know where you are, all the time. DME or not.

 

[PropsForward]

just turn when the 430 or 530 tells you to...

Yeah, them 430's sure are nice.

 

[Flylo]

What did your instructor tell you? He should tell you to look it up from an official source, not here. Start studying the AIM. To make it easy, try 5-3-5. Waiting for station passage may be OK in a 100 kt ground speed trainor, but not in a faster aircraft or strong tail wind.

Thank all of you for the answers you gave.

I read 5-3-5 in the AIM and 14 CFR 91.181 and have decided that "Full Flaps", my instructor, was probably right when he said I could cut the corner at 4 NM from the VOR.

The question I asked came up because of a route I was flying on a simulator and I may not have made it perfectly clear what I wanted to know.

I took off from a small airport and was told to fly direct to a nearby VOR climbing to 4000', intercept an airway radial there and fly that radial to the next intersection.

For the sake of clarity lets say the I was flying a heading of 360* to the VOR (180* radial) and, the airway I'm going fly when leaving the VOR is the 280* radial. So, in effect, I'm making a hard left turn.

The reason I asked the question is because: I'm CHEAP!! I didn't see any reason to be paying for that high dollar simulator (or a real airplane for that matter) when I know I'm just going to the VOR and then coming right back to darn near the same place, so I asked how close I was legaly "required" to get before I could turn (the simulator does have DME)? Based upon the answers I've read here and not finding anything that specifically says otherwise in the regs; I don't believe anyone is going to give me any trouble if I make the turn 4 NM (the edge of the airway) from the VOR, unless I was very close to my destination airport and involved in an ATC directed traffic pattern or arrival procedure.

It's nice to know that "Full Flaps" has some idea of what he's talking about but it never hurts to check.

Thanks again.

.

 

[A Squared]

I don't believe anyone is going to give me any trouble if I make the turn 4 NM (the edge of the airway) from the VOR, unless I was very close to my destination airport and involved in an ATC directed traffic pattern or arrival procedure.

Uhhhh, I wouldn't say that. Yes, there is some tolerance, and it is good to have an idea of what that tolerance is....but, you should never be intending to use that tolerence. Operationally, it is hard to defend doing anything but your best attempt to remain on the centerline of where you should be. If you are cleared on an airway, you should be on the centerline, if you're not on the centerline, you should be correcting back. If you're cleared on a radial, you should be making your best attempt to fly that radial. Sure, leading the turn a little to intercept is fine. leading the turn to intercept the edge of the airspace. Uh,uh, particularly in the terminal environment, 4 miles might raise some eyebrows, or even cause problems for ATC

 

[TonyC]

Like A Squared said, it is proper to turn before sation passage in an effort to fly from centerline to centerline. Turning earlier than that because you know there is a tolerance or width is improper.


In the example you specified, you arrive at station XYZ on a 360 course, and you plan to depart the station on the 280 course -- an 80 degree left turn. It is proper to begin the turn approximately one turn radius' distance prior to reaching the station. If your groundspeed is 120 Kts, and you use the 1% of groundspeed method to determine turn radius, you should begin the turn approximately 1.2NM prior to reaching the station - - not 4.


Your goal should be centerline.

 

[crudeoilpilot]

Did we make a turn

Tony; you did mean to say the 280 course I'm guessing. You're right, the groundspeed trick works perfect. A 90 degree turn at 250 kts, start at 2.5 miles etc. to fine tune it take your 90 degree window in your HSI and divide it into 3 sections, if you have a 60 degree turn at your 250 kts use 1.8 miles, a 30 degree use .8. Leading early for passenger comfort or should I say less drink spillage is easy to accomodate with this rule.

 

[TonyC]

Tony; you did mean to say the 280 course I'm guessing.

Why, of course that's what I meant! My eyes were too blurry to notice the error; thanks for the help!

Next stop, the EDIT button!

 

[coonass one]

The way I do it:

No matter what altitude, at 4 nm prior (corrected for slant error on the dme) I set up a 20-30 degree intercept, and just wait a few seconds. Works out well most of the time(depending on speed of course).

 

[philo beddoe]

I use 1% of GS minus .5 nm, which works well for me. But then again, I tend to roll into turns with a fair amount of enthusiasm. This rule works pretty good with arcs as well, since it is better to be a tiny bit late turning onto the arc than be too early. Which brings up another point: why does every one teach a 90 degree turn onto the arc? Since you are going to join further along the arc as you turn, an 80 degree turn works better, since you will not have to immediately turn again just to maintain the arc.