Beyond the I-11? Here's one outta HHR

[Keith Smith]

Mark,

That would not be a legal way of flying that route, as far as I know. Regulations exist which state that pilots will fly along the center of an airway.

Some of the solutions that have been proposed are completely workable. What's neat about this is that there are a number of ways of doing it. I didn't even know you could have the G-1000 setup a user-defined waypoint at the intersection of two radials.

This is going to be an advanced topic, but VOR radials and GPS courses are not the same thing. That is, if you tracked the VTU 180 radial for, say, 40nm, then asked the GPS for the direct heading to VTU, it may not be 360, as you'd expect. However, the delta between the GPS course and the VOR radial at short distances (like the one to ELB from V64) is so slight that it would be inconsequential. It is something to keep in mind, though, as you get further away.

Other than Orest's creative solution, this is going to require the use of a VOR. I would fly it by navigating along V64 (either with a VOR, or by GPS), then setup an unused NAV radio to identify when I'm approaching the V363 (by setting the OBS to 145 so I can track the ELB R-325 inbound).

All that said, I did just think of a way to make it happen with a standard GPS-only solution. You could program LIMBO SLI TUSTI COREL JOGIT ELB DANAH OCN KCRQ into the flight plan on the GPS. After passing TUSTI, I would note my heading (which is, presumably, keeping me centered on V64), then use the 'activate leg' feature on the GPS to activate the JOGIT-ELB leg. Note: this is NOT the same as going direct JOGIT, which would be a mistake. We're holding a heading on V64 and the GPS course is now set for the course between JOGIT and ELB (V363). You would hold the heading until the CDI showed you were joining V363 and then you'd make the right turn to the 145 course (that's an approximation, reference the discussion about radials vs GPS courses above).

It's an interesting route, no matter what method you use to solve the problem. What I love about it is that it gets you thinking about how to navigate along a cleared route under a slightly different circumstance.

Ironically, the least complicated way of doing this would be to leave the GPS switched off and just use 2 NAV radios. In fact, people who grew up with VOR navigation are likely looking at this and saying, "what's the big deal? It's just one radial intersecting another...there's just no named intersection there." And they'd be bang on

[Orest Skrypuch]

Mark,

Perfectly koshire. Remember that the airways we fly are at least 8 nm wide. They were designed in times when straightline navigation was not as accurate as now, and to allow for the flyover and then a turn and reintercept method for flying the next leg.

On PE I prefer to rely on basic VOR/NDB nav, to stay in practice. Although I fly with primary reliance on GPS and moving maps RW, the VORs are always tuned and ready. I did lose my Garmin once enroute, and it was a snap to switch over. Another reason to file some VORs instead of direct.

[Orest Skrypuch]

Well Keith and I cross posted, not intending to debate, but you have to consider the history, the regs were built on that. Although you should always attempt to fly the center of the airways, with non-gps nav it is near impossible.

[Peter Grey]

A couple of technical notes:

Per TSO C129a (the certification rules for GPS), most GPS's (anything thats standalone) must have the ability to input a user waypoint via lat long or RBD. Additionally the OBS mode mentioned before must also exist.

Note you can get around the angular difference problem (the GPS using a different magnetic variation database then the preset VOR data) by asking the GPS what the track from SLI to COREL is and from ELB to JOGIT is, then using those bearings to input your user waypoint, however for such a short leg I wouldn't bother.

[Mark Hargrove]

Keith,

OK, your GPS-only solution is very, very clever -- I never thought about using a course that went back and intersected itself!

When I was flying in the real world (back in the Paleozoic era) I also grew up with just VOR navigation and realized that this is indeed easy to fly with 2 VORs. What I'm noticing in "modern" aircraft, though (at least, in those available as add-ons to FSX) is that very few of them have dual VOR receivers if they have a GPS receiver. The sim version of the Garmin G1000 glass cockpits (the good ones, from Flight1 and others -- not the horrible implementation on the stock FSX plans) have bearing indicators for both VORs, but it seems that you can only dial in an OBS heading on NAV1 -- the NAV2 radio will display a bearing, but it's not adjustable to let you nicely set up an intercept when the bearing arrow is straight up. You can still note the intercept when the bearing arrow points to the actual VOR radial you care about (kinda like using it as an NDB receiver) -- but the gradations on the compass rose are pretty small for my aging eyes.

Life is full of compromises, I guess!

[Keith Smith]

Orest,

I have to laugh at the fact that our posts are polar opposites regarding Mark's initial solution that uses the ded reckoning leg. I agree, VOR's are not as precise, but if you were on a check ride and you attempted to INTERCEPT and fly along an airway using nothing but ded reckoning, ignoring the VOR option, I suspect it would be an issue. What say you?

Btw, this is exactly what I was hoping would happen when I posted the question. It's an excellent discussion.

[Orest Skrypuch]

The discussion is excellrnt. We are creating an artificial situation and trying to find all the possible ways to fly it. On a ride you would use the most accurate method available to you. But if you do not have rnav and there is no dme on the VOR you have no choice but to overfly and reintecept. Airwsy corners actually have additional safety zones to allow for extended turns.

Sorry for the typos Im at slopeside lunch and on a phone, skiing in the west, just had to join in.

[Keith Smith]

The discussion is excellrnt. We are creating an artificial situation and trying to find all the possible ways to fly it. On a ride you would use the most accurate method available to you. But if you do not have rnav and there is no dme on the VOR you have no choice but to overfly and reintecept. Airwsy corners actually have additional safety zones to allow for extended turns.

They do, that's true, but I disagree that you need rnav or DME to avoid overlying and reintercepting. Even with just two VOR's and no RNAV, you could fly this fairly precisely, no need to overfly the El Toro radial, you can see the needle coming in (without DME) and make the turn to join it.

Sorry for the typos Im at slopeside lunch and on a phone, skiing in the west, just had to join in.

Sound REALLY, REALLY tough. I hope you get through that ordeal without any serious emotional scarring.

[Orest Skrypuch]

Keith,

Well, it depends on how far away the next VOR is, if it is an long enroute leg, the next (H) VOR could be 100nm, and may not give you very accurate guidance with your NAV/CDI being +/- 4 deg. Entirely agreed that in the current example we are discussing that is not an issue.


But, also consider the situation of flying inbound to a VOR, whose radial outbound then leads to a feeder route for an approach. If DME is not available (by navaid or the aircraft), then you will have to look for the null zone (TO/FROM switchover), and then make the turn promptly and reintercept by correction.

Now yes, these hoof-beats are zebras rather then horses, but these situations do occasionally crop up. Always best to be prepared for any curves we get out there.


And yes, I'm having an awful time out here, with all the snow coming down, and the snow ghost trees, and pristine powder in the trees. I'm really ready for the hot tub at the end of the day, I'm afraid.

* Orest

[Orest Skrypuch]

The difference between VOR radials and GPS tracks was mentioned. The first is a rhumb line (loxodrome) which is a course that has the same angle of intersection with each line of longitude, the other is an arc of a great circle route (orthodrome). A rhumb line, if continually extended will always spiral in to one of the poles. In marked contrast, a great circle route will eventually rejoin itself, after a complete revolution.

Over short distances there is no significant difference, but over 100nm there is a measurable deviation in terms of aviation -- but not enough to put you out of an airway, or cause other nav issues. So even with perfectly tuned radio equipment, flying a radial accurately will put you into a slightly different location, than flying a GPS track.

One other interesting factoid is that mapped airway radials are changed from time to time. This not only reflects changing magnetic variation, but also takes into account errors/changes in the VOR broadcast either due to equipment limitations, local geography, or a VOR recalibration. The GPS of course ignores all that, and gives you the true geometric course.

Now, down in the virtual world, we have one other confounding factor. Depending on what simulator you are using, the MagVar of the navaids in the sim may be significantly out of tune with the RW, and any of the current day maps and charts you are using! Although magnetic variation changes continually and gradually, the standards are only changed once in every 5 years. FS9 is ten years out, FSX is five years out. (both are somewhat fixable with a cool tweak to some of the BGLs) Perhaps X-plane is on the money, I don't know. If you find that the radials from one VOR to the next don't match up in FS at the changeover point, that is one of the major reasons.

* Orest