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.