VOR DME B (KMDQ)

[Mistake Not...]

http://155.178.201.160/d-tpp/1611/05924VDB.PDF

I'm having trouble seeing how it's even possible. Obviously it is, but based on my understanding of when you can descend, I don't see how.

You can't descend to a lower altitude unless you're on the segment. As you can see, when you cross the VOR and are on the 043 radial outbound, you can descend to 2020. My confusion (and frustration) seems to come from trying to determine when im actually on that segment. That close to the VOR, the CDI is still full scale and just starting to come in. I thought I read somewhere that you're considered on a segment with less than half scale deflection. You don't get that until it's (IMHO) way too late to reach 2020 with a less than 1000fpm rate of descent.

Help? How should this be flown? What indication am I looking for after crossing RQZ?

 

[Mistake Not...]

Well I'd fly it by being at 2900 on course 070 inbound to RQZ. After passing RQZ I'll turn to 043 and simultaneously initiate a non-precision desent rate of 800 fpm. Assuming Cat A you need to lose 1400 feet to get down to the circling MDA in 4.9 miles. At 90 KTS that's just over 3 min which is enough time to lose the 1400 feet.

Agreed. No wind, this would work, but to me it seems like a special case. When you said "turn to 043" and initiate a descent, you're doing it by heading and not by VOR indication. But that segment isn't defined by heading, it's defined by the VOR radial. And depending on what it means to be on such a segment, you couldn't start down when crossing the VOR. You'd have to wait. Throw in a strong cross wind, and turning 043 doesn't get you on the segment.

I'm beginning to think the "wink wink nudge nudge" of this approach is that the protected area either side of the 043 segment is wide enough to just allow you to do exactly what you suggested. But, is it a check ride bust to have full scale deflection and still begin a descent?

 

[jordane93]

Once you cross back over the VOR you can initiate your descent to HUTUN and you're going to track the 043 radial. 043 isn't a heading, it's a radial. You turn to whatever is going to center up that OBS

 

[Mistake Not...]

Yes. I guess I'm having a hard time describing this.... that close to the station, you don't get a trackable indication until a few miles out. At least I don't.

Does the CDI have to be centered before starting descent? Half scale deflection? doesn't matter, since we crossed RQZ?

 

[RotorDude]

All the above. You are on the new segment as soon as the needle flips, even if it pegs to one side momentarily. You should have a reasonable idea of the needed wind correction so you should turn to the heading that you think will center the needle on the new radial and start descending immediately. If your initial heading guess is off, then keep working on it, trying to get it centered. This isn't rocket science, just your basic steam gauge instrument approach, so don't overthink it.

 

[MauleSkinner]

I thought I read somewhere that you're considered on a segment with less than half scale deflection.

First thing I'd suggest is finding where you thought you read that.

 

[Gucci Pilot]

I know what you are asking, you're talking about the cone of confusion. I did a VOR approach like this on my instrument checkride. It didn't have the bend, but the VOR was the FAF. What would I do? I would already have a good idea of the winds. The second that to/from flag flips I would spin in the radial and start going to a heading I think will give me a 043 track. Give it a few seconds then fight for that centered CDI. Once I'm within half I would start down. Why wouldn't I just start down before the CDI centers? What if I spun the reciprocal in and thought I was tracking towards the center when actually I am going away from it and now going down? If you are flying this approach at 90 knots in your trusty 172, the descent requires less than 500 ft./min. past the VOR and the final segment after HUTUN requires even less(yes I know it is a circling approach but you have options to circle if you hit 1500 right at 4.9) so no need to be right at 2020 at HUTUN. You have a little time to get on track then go down. If you flew this approach at 90 knots, you could do 800 ft./minute 2.3 miles past the VOR and still make it down to 1500 at the MAP. That is a whole minute and a half past the VOR. It shouldn't take 1.5 minutes to get out of the cone of confusion.

Even better, if you have an IFR certified GPS, use that.

 

[luvflyin]

............................................................................................................
.......Does the CDI have to be centered before starting descent? Half scale deflection? doesn't matter, since we crossed RQZ?

You need station passage. Thats a TO/FROM flip.
THROTTLE, TURN, TIME, TWIST, TALK
Turn, Twist, Time, Throttle, Talk
and other variations.
I've never seen Twist come before Turn. Like has been said above, make the turn to your best guess of what the holding heading will be. You are on the final segement when you have station passage. I would start down right away on that approach, but waiting for a more positive needle indication is fine.

 

[MAKG1]

Yes. I guess I'm having a hard time describing this.... that close to the station, you don't get a trackable indication until a few miles out. At least I don't.

Does the CDI have to be centered before starting descent? Half scale deflection? doesn't matter, since we crossed RQZ?

No. You're well within protected airspace anywhere in the zone of confusion. Turn to the heading you think will produce 043 course, and descend immediately upon passing the VOR. When the needle comes alive, intercept it. You may be many "degrees" off course, but in terms of distance, you're very close -- probably within a few tenths of a mile. VOR approaches have very large protected zones. They have to.

Gucci Pilot, if you spin in the reciprocal, fly the reversed sense, or just fix it. It's not hard. I did that the first time I flew a back course DP (i.e., outbound), and that had a much more sensitive CDI.

 

[aterpster]

The VOR approach protected airspace is +/- 1 n.m. at the VOR and where the VOR is the FAF.

 

[denverpilot]

This is similar to the KLNK VOR 17 (as opposed to the VOR 18) approach.

You're in pretty close and if you have a slow TO/FROM flipping OBS, you'd better start the decent and the turn as soon as it goes in between TO/FROM, or you're not gonna make it if you have a tailwind component.

Pay attention to winds and just make the turn including any wind correction angle right off the bat. You'll have a short period of time when the needle comes back to tweak over onto the course and then it's either see the runway or go missed.

Couple of miles to the VDP is all ya got.

@jesse can start chuckling now at my slow-ass King OBS TO/FROM flip in my airplane. He's seen it.

That example is a lower angle turn than your example, but it's the same concept and you've only got a mile or so of solid indication after going over the VOR. If you wait to turn, you'll be (literally) on the VOR 18 approach instead of the VOR 17. Kinda. Look at the differences.

To get to runway 17 you just hang a quick left at Albuquerque, as Bugs would say.

 

[luvflyin]

Yeah, that's a quick one. But I definetly wouldn't start down a little earlier than TO/FROM flip if I was nice and stabilized and knew I was over LNK. Really, I wouldn't cheat, I promise.
What's the story on that being Rwy 17 instead of 18L?

 

[Tflhndn]

At 2200' above the VOR, you should have a readable signal within a 1/2 mile after passing it.

At 90kts that's less than 30 seconds after station passage. And you still have 4 miles to the MAP.

I would wait to get positive course guidance (less than full deflection) and descend.

 

[aterpster]

At 2200' above the VOR, you should have a readable signal within a 1/2 mile after passing it.

At 90kts that's less than 30 seconds after station passage. And you still have 4 miles to the MAP.

I would wait to get positive course guidance (less than full deflection) and descend.

Why do you need to wait for that? If your tracking to the station was reasonable, and the two-from flag goes to from, you turn to an intercept heading and start down.

 

[Tflhndn]

Why do you need to wait for that? If your tracking to the station was reasonable, and the two-from flag goes to from, you turn to an intercept heading and start down.

Duplicate post - deleted.

 

[Tflhndn]

Why do you need to wait for that? If your tracking to the station was reasonable, and the two-from flag goes to from, you turn to an intercept heading and start down.

I agree you make the turn at the flag flip, but I was taught (and read - but no citation available right now), that before you can begin/continue a descent at/after a VOR (below minimum height for the inbound leg), you must have positive course guidance on the CDI - I.e, something other than the needle at full deflection.

In this case, until you have reacquired the vor 43degree radial with less than full needle deflection, you cannot descend below 2900'

As soon as the needle comes back in, you are on your way to 2020, which you of course hold until you get to the 2.8Dme (HUTUN)

 

[flyingron]

If you think you're off course so much to be an issue in this case, it matters little if you are at the previous segment altitude or the following one.

 

[denverpilot]

(The same reason you only move the CDI 10 degrees at a time on a DME arc - you are expected to maintain positive course guidance throughout the approach)

Your course *is* the DME arc. The OBS isn't providing any course guidance at all, it's just telling you how far along the arc you are. It's just showing cross-radials. You could spin it all the way around or even fail it and still fly the arc using the DME reading and the mag compass or DG. (Plus a little help from knowing where the wind is from...)

The needle is NOT providing you positive course guidance on a DME arc, flown the old fashioned way without a GPS anyway. The DME counting up or down or holding steady is.

( @jesse enjoyed failing half my panel at the turn onto an arc once upon a time... grin... How one learns that flying a DME arc at night with nothing but a mag compass is a really interesting way to try to kill yourself if your brain gets overloaded... )

 

[jsstevens]

Your course *is* the DME arc. The OBS isn't providing any course guidance at all, it's just telling you how far along the arc you are. It's just showing cross-radials. You could spin it all the way around or even fail it and still fly the arc using the DME reading and the mag compass or DG. (Plus a little help from knowing where the wind is from...)

The needle is NOT providing you positive course guidance on a DME arc, flown the old fashioned way without a GPS anyway. The DME counting up or down or holding steady is.

( @jesse enjoyed failing half my panel at the turn onto an arc once upon a time... grin... How one learns that flying a DME arc at night with nothing but a mag compass is a really interesting way to try to kill yourself if your brain gets overloaded... )

If I'm going to kill myself, I want it to be interesting. Or just skip the whole thing.

 

[Mistake Not...]

I agree you make the turn at the flag flip, but I was taught (and read - but no citation available right now), that before you can begin/continue a descent at/after a VOR (below minimum height for the inbound leg), you must have positive course guidance on the CDI - I.e, something other than the needle at full deflection.

In this case, until you have reacquired the vor 43degree radial with less than full needle deflection, you cannot descend below 2900'

I think this is the magic phrase I was struggling to find, but couldn't. My flight instructor has been very clear about how to fly this approach (he agrees with all of you, turn to 043 after crossing RQZ). But from a "technically correct" (which is the best kind of correct) point of view, I was wondering what indications I needed to have before descending.

I still can't find anything that, in general, says when I'm "on" a segment. The PTS says no more than 3/4 scale deflection. Using that, I'd expect to try to get less than 3/4scale of the CDI, -then- start down. My inexperience probably makes this a lot harder than it is. Stuff happens awfully fast after RQZ, especially if you're waiting for the needle to come in.

Thanks everyone.

 

[MauleSkinner]

I still can't find anything that, in general, says when I'm "on" a segment. The PTS says no more than 3/4 scale deflection. Using that, I'd expect to try to get less than 3/4scale of the CDI, -then- start down. My inexperience probably makes this a lot harder than it is. Stuff happens awfully fast after RQZ, especially if you're waiting for the needle to come in.

The PTS reference applies to maintaining a course, not intercepting it...

Applies proper correction to maintain a course, allowing no more than 3⁄4-scale deflection of the CDI or within ±10° in case of an RMI.

 

[aterpster]

The PTS reference applies to maintaining a course, not intercepting it...

Exactly.

 

[Mistake Not...]

Ok. Then when I have intercepted it? I'm sure this has been asked and answered a billion times but a quick search and google didn't turn up as much I would have thought. Say I'm getting vectors for the localizer... when can I descend to the altitude for that segment?

 

[jordane93]

Ok. Then when I have intercepted it? I'm sure this has been asked and answered a billion times but a quick search and google didn't turn up as much I would have thought. Say I'm getting vectors for the localizer... when can I descend to the altitude for that segment?

When you're established.

"Cessna 12345, turn left heading XXX, maintain XXXX until established, cleared for the ILS XX."

You're established when the needle comes off the peg.

 

[bobmrg]

I agree you make the turn at the flag flip, but I was taught (and read - but no citation available right now), that before you can begin/continue a descent at/after a VOR (below minimum height for the inbound leg), you must have positive course guidance on the CDI - I.e, something other than the needle at full deflection.

In this case, until you have reacquired the vor 43degree radial with less than full needle deflection, you cannot descend below 2900'

It would be interesting to read the citation when you find it. If you do not, it is another example of taking an instructors word as gospel without documentation. "Where can I find that it the regs/AIM?" is always a valid question. Note the student's creed below my signature.

Bob Gardner

 

[Tflhndn]

Bob,

I don't recall thumping my chest and stating this is the way it is... I was only putting out my understanding of it - and the source of my understanding.

Seems to me that is the opposite of believe it is gospel.

 

[Brad Z]

I agree you make the turn at the flag flip, but I was taught (and read - but no citation available right now), that before you can begin/continue a descent at/after a VOR (below minimum height for the inbound leg), you must have positive course guidance on the CDI - I.e, something other than the needle at full deflection.

In this case, until you have reacquired the vor 43degree radial with less than full needle deflection, you cannot descend below 2900'

As soon as the needle comes back in, you are on your way to 2020, which you of course hold until you get to the 2.8Dme (HUTUN)

I think this is the magic phrase I was struggling to find, but couldn't. My flight instructor has been very clear about how to fly this approach (he agrees with all of you, turn to 043 after crossing RQZ). But from a "technically correct" (which is the best kind of correct) point of view, I was wondering what indications I needed to have before descending.

I still can't find anything that, in general, says when I'm "on" a segment. The PTS says no more than 3/4 scale deflection. Using that, I'd expect to try to get less than 3/4scale of the CDI, -then- start down. My inexperience probably makes this a lot harder than it is. Stuff happens awfully fast after RQZ, especially if you're waiting for the needle to come in.

Sounds like y'all have the same instructor.

Those of us who have been flying instrument approaches back in the dark pre-GPS days know that on a VOR approach you're gonna have full scale deflection crossing the VOR, particularly if there's a turn right at the navaid and you have to reintercept the new radial. As others have mentioned, you're in protected airspace at that point so you can initiate your descent.

It wouldn't surprise me if there was some local chief instructor or DPE who insisted that you can't begin your descent until you've reintercepted the new radial, but they would be wrong.

Now if for some reason you cannot reintercept the radial in a reasonable amount of time you should initiate a missed approach, but a prudent pilot will plan on turning to a heading that will assure a quick reintercept, based on the direction of the turn and winds aloft.

 

[aterpster]

Sounds like y'all have the same instructor.

Those of us who have been flying instrument approaches back in the dark pre-GPS days know that on a VOR approach you're gonna have full scale deflection crossing the VOR, particularly if there's a turn right at the navaid and you have to reintercept the new radial. As others have mentioned, you're in protected airspace at that point so you can initiate your descent.

It wouldn't surprise me if there was some local chief instructor or DPE who insisted that you can't begin your descent until you've reintercepted the new radial, but they would be wrong.

Now if for some reason you cannot reintercept the radial in a reasonable amount of time you should initiate a missed approach, but a prudent pilot will plan on turning to a heading that will assure a quick reintercept, based on the direction of the turn and winds aloft.

There is as much bogus information floating around as there are CFI-Is. Most of them are young pups who have recently learned from other young pups.

As you know, where a VOR station is the FAF, and there is a course change from the intermediate to the final segment things appear to happen rapidly because the FAF (station) is in the area of ambiguity. If the tracking was good until close to the station, it's going to be good after the station assuming the pilot establishes a reasonable intercept heading for the final segment course. To delay descent until outbound tracking is "happy" is bad procedure...period. This is the final segment, the most critical segment of an IAP. Criteria is predicated on beginning descent at the FAF and, if required, starting the clock at the FAF. The maximum course change allowed by criteria is 30 degrees and it can't be that much unless the final segment is at least of defined length.