Just short of a Six Pack!

When making my own VDP, I take Richard Collins' advice of creating (or continuing) the stable descent rate shown or implied by the plate. So, in this case, If I am descending at 90 knots (ground speed), and I am using that 3.03 descent angle, I am descending at roughly 480 fpm. The ARC is at 14.7 miles which means that every four degrees equals almost a mile of travel. At Radial 047, the minimum was 1260', and the MDA is 900'. I need to lose 360 feet from Radial 047, which will take me 45 seconds. Again, using that stable descent rate, and travelling at 1.5 miles per minute, in 45 seconds I will have traveled 1.12 miles over the ground and have reached the MDA a bit beyond the 051 radial. This is just beyond two miles from the runway. IF and ONLY IF I have the runway environment in sight (meaning, more visibility then required for one-mile for Class A aircraft) and am below the clouds, I will simply continue this stable descent rate which will give me a TCH of 55. Now then, since I want a stable descent rate from my home-brewed VDP, I will not commence a descent to the runway before the 051 Radial if, for some reason, I got down to the MDA a bit early.

Now in actual practice, I might have to level off. . . /ubbthreads/images/graemlins/confused.gif
 
Disagree with Collins' advice. The problem I personally have with the constant descent rate is that you're now treating a non-precision approach like a precision approach. The key to a non-precision, IMO, is to get down from the FAF or the last intermediate letdown to MDA pronto, so as to have the maximum time to search for the airport and/or runway environment from the already high (comparitively to a precision IAP) altitude you're at. By descending at a constant descent angle and reaching MDA at the VDP, you're cheating yourself of time available to search for the runway, without even being able to get the lower altitude that a DH on a precision approach would give you. At least with a DH, even though you have a second or two to make the continue or go-around decision, you're much closer to the runway than you'd be on a non-precision.

Might want to put that into your bag of learning tricks. Could make a difference in the future. You never want to cheat yourself out of anything available to you.
 
Thanks, Mike. I always take very seriously the advice of professionals like you. I understand your points, and I definitely will give them careful thought.

Thanks, again for taking so much time with me!

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Disagree with Collins' advice. The problem I personally have with the constant descent rate is that you're now treating a non-precision approach like a precision approach. The key to a non-precision, IMO, is to get down from the FAF or the last intermediate letdown to MDA pronto, so as to have the maximum time to search for the airport and/or runway environment from the already high (comparitively to a precision IAP) altitude you're at. By descending at a constant descent angle and reaching MDA at the VDP, you're cheating yourself of time available to search for the runway, without even being able to get the lower altitude that a DH on a precision approach would give you. At least with a DH, even though you have a second or two to make the continue or go-around decision, you're much closer to the runway than you'd be on a non-precision.

Might want to put that into your bag of learning tricks. Could make a difference in the future. You never want to cheat yourself out of anything available to you.

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I've just been in too many situations where the WX has been close enough or ragged enough, etc, that getting down early made the difference. Also, by Collins' method, though the approach may look pretty and stabilized at a shallow descent angle, nothing guarantees that you'll arrive at MDA when you hit the VDP. By not having formal glidepath guidance (such as a glideslope needle), other than an unreliable VSI indication, if for any reason you overshoot the VDP by the time you reach MDA or see the runway, you're screwed.....and either going around, or making some crazy-ass descent to the runway....the former option prudent but should have been unnecessary, while the other option is plain unsafe.

It's best not to put yourself in that corner when you don't have to. There may come a day when you're low on fuel, you're at your divert base or maybe there isn't one (unforseen WX), and you force yourself into a go-around just because you screwed yourself out of time to find the runway by not getting down to where you needed to be at the earliest opportunity (non-precision descent rate). While Collins' technique is procedurally correct, it's not the best technique to be using. There's been too many times where I've tested that real-life. If I were giving you a checkride, I wouldn't ding you at all for using Collins' technique, I'd just take the evaluator hat off and put the instructor hat on, and debrief you on the technique like I'm doing now, after grading you good for flying the approach well (pending you did). /ubbthreads/images/graemlins/smile.gif.
 
Thanks, again. Yes, I see what you're saying. It is nice to be stabilized all the way down, and it is nice to fly nonprecision approaches as much like precision approaches as possible; but I do see what you mean about possibly losing your chance to land.

In general, I do try to get to the MDA well before the MAP for just those reasons you point out. If there's a printed VDP in the procedure, of course I have to wait for it; but if not--well, you're right, best to get down to the MDA so you can get ready to land.

Again, I really appreciate your time. Now, let's just see if my CFII makes me fly that approach partial panel! /ubbthreads/images/graemlins/spin2.gif
 
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In general, I do try to get to the MDA well before the MAP for just those reasons you point out. If there's a printed VDP in the procedure, of course I have to wait for it; but if not--well, you're right, best to get down to the MDA so you can get ready to land.



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Even if there's no printed VDP, it behooves you to compute one as a point of reference for the descent angle you desire. As an IP, I look for studs to have done their homework on approach plates. That is, seeing a VDP computed and marked if there wasn't one. If there's any radials to arcs, then I expect to see a lead DME noted. Likewise for arcs to radials, I expect to see lead radials annotated if there are none. Between intermediate altitudes, it's good to see descent angles noted (rise over run) so not to miss "hard" intermediate altitudes, if any. It's just the little things that show a guy has done his homework. Not as much importance real-world for Category A aircraft, but good practice for the Cat C/D/E aircraft you might get into later.
 
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Sometimes, when partial panel gets to the point where you're left with a hobbs meter and an oil pressure gauge, you've just gotta know when to roll inverted and pull.......it's your last option anyway, may as well go out with a bang.

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Less messy. Just cover up the hole with some dirt and put up a marker that says something like: "He died avoiding a school house".
 
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