For advisory altitudes like the CDFA descent profile, yes you can.
Ok. Then amending plates, to easily cross check with G1000 database, is by far the best option to get advisory altitudes for CDFA profile. Much better than involving DME.
JasonC wrote:
If you are doing it as a CDFA you need the check altitudes to know if you are on the profile.
I teach the descent on the Final Approach differently, and in a way that works on all approaches, which is to focus almost exclusively on RoD and GS. I also reinforce the teaching by covering up the GS on an ILS approach and getting students to fly RoD, then, surprise, surprise, at DA they are precisely on the GS.
For a 3° slope, we all know that we need to descend 318’/nm, which, for ease of calculation, we often call 300’/nm. That means that at 60kts we need 300fpm, at 90kts, 450fpm and 120kts, 600fpm. Other groundspeeds are available.
This is not a “rule of thumb”, it is a Euclidian certainty.
If you fly the Intermediate Segment at the configuration, power and trim you are going to use for the approach, but gear up, then, in everything I have flown, drop the gear just before the FAF, without changing anything else (I get students to do it hands off the controls) the aircraft will fly, pretty closely, a 3° slope (depending on headwind, but within the ballpark.) In fixed gear aircraft you need to experiment, but generally there will be a precise number of inches of manifold pressure, or maybe dropping flaps, that will have the same effect.
That means that during that stable Intermediate Segment you can plan you RoD pretty accurately. You can even do it for 320 or 330 ft per nm (330 being +10%) if you are good with sums. That, together with bracketing the heading, is why you want a stable Intermediate Segment.
So you arrive at the FAF with a very accurate idea of your required RoD, all you then have to do is adjust either the RoD for the GS achieved, or adjust GS with power for the RoD calculated, and Bob’s your uncle. You can even calculate the GS required for a round number RoD (113 kts requires exactly 600fpm on a 3° slope). This is particularly useful if you have an autopilot that does VS only in multiples of 100fpm.
Once you get used to the fact that that RoD, accurately flown, will, without doubt, give you your check altitudes, GS or GP within a whisker, you can be a little less concerned about the check altitudes.
In addition, of course, if you have SynVis you can also ensure that the target is dancing around the threshold.
Timothy wrote:
I teach the descent on the Final Approach differently, and in a way that works on all approaches, which is to focus almost exclusively on RoD and GS. I also reinforce the teaching by covering up the GS on an ILS approach and getting students to fly RoD, then, surprise, surprise, at DA they are precisely on the GS.
For a 3° slope, we all know that we need to descend 318’/nm, which, for ease of calculation, we often call 300’/nm. That means that at 60kts we need 300fpm, at 90kts, 450fpm and 120kts, 600fpm. Other groundspeeds are available.
This is not a “rule of thumb”, it is a Euclidian certainty.
This works if don’t have 40 kts of headwind 
For any wind component along your track that is different than zero you have to have the ability to cross check distance with altitude.
This works if don’t have 40 kts of headwind
And if you do. We are talking GS. Do the sums.
For any wind component along your track that is different than zero you have to have the ability to cross check distance with altitude.
Nope. Do the sums.
What doesn’t matter is your IAS or TAS. The only thing that matters is your GS. So whether you are going down the slope at 70kts because you are in a C172 in nil wind, or because you are a Navajo doing 120kts against a 50kt headwind component makes no difference. You need to calculate 300 (or 318) ft per nm for the GS you are doing.
Timothy wrote:
I teach the descent on the Final Approach differently, and in a way that works on all approaches, which is to focus almost exclusively on RoD and GS. I also reinforce the teaching by covering up the GS on an ILS approach and getting students to fly RoD, then, surprise, surprise, at DA they are precisely on the GS.
I don’t see the difference. Of course you should fly any approach using RoD and GS but you should still check the altitudes on a CDFA just as you still check the glideslope needle on an ILS approach.
Airborne_Again wrote:
I don’t see the difference.
The way Jason expressed it, it sounded like the check altitudes came first. My view is that the RoD/GS method is so reliable (a mathematical certainty) that ones doesn’t need to fuss too much about the check altitudes. They just happen, because they have to happen.
The guidance document for the IR is interpreted to mean that the +/-100 foot standard (before DA which requires go around to be initiated at +50 /- zero and definitely not a dive and drive), is referenced every mile between the FAF and the DA, advising whether high, low, on profile and correcting accordingly. In practice the standard is closer to +/- 50 feet. Consistently being at the limit of the Basic Guidance Document 01, would not be regarded as flying a CDFA, nor would a jet assessment by a commercial carrier regard it as acceptable.
Doesn’t address how to fly the CDFA where the profile mileage does not agree with the miles to fly over final waypoint. This does seem odd, and marking up a plate as a work around also would be non standard.
And if you do. We are talking GS. Do the sums.
You’re correct. I didn’t understand that in your original post you were referring to ground speed – I thought that GS was glide slope and was totally confused
