Denver

But I do not have an FMS?

On the subject of VDP and CANPA. You can still do a mental CANPA (as far as hitting each fix at the required stepdown) on any approach and this applies all the way down to the MDA. I do a mental CANPA down to the FAF and then it is steep to the MDA. I like to get down early.

Now since this is circling only and at least in a 421 I could never make the strait in and would always have to make the circle back to 30. Even with the new runway I find it dicey while trying not to back drive the engines. In the circling environment you are only provided 300 feet of obst clearance anyway and if the runway has a vasi you had better remain at the altitude until picking it up (Unless you know where every stickieuppie is). In a legal sense I always have to ask for the visual if runway in sight before the FAF. When the ceiling is lower than the altitude on the FAF I know I will always circle.

rickair7777

FMS has nothing to do with CANPA.

In it's basic form you simply calculate a vertical speed (based on ground speed) from the FAF (or other appropriate descent point) that will give you a glide path which will get to MDA (we add 50' so we don't bust it) at about the MAP. You still have to clear intermediate step downs, but in almost all cases you will if you do it right. The FAA doesn't usually publish step downs that are too far outside of a "normal" approach angle...that would make for unstabilized approaches.

Yes, you can use it on a LOC or other non-prec approach, that's what it's for...no need for CANPA on an ILS or other approach with vertical guidance.

You can do a steep descent to get down early but then you have to level off...the ideal way to do a CANPA is to arrive at MAP or VDP almost at MDA so you either continue the descent or go missed.

galaxy flyer

Rickair7777

I'm talking about real CANPA, not a "that looks bout right" guess what angle goes from the FAF to the MAP. There ISN'T an angle printed on the KSMX chart to any LOC-based chart. It is not possible for an FMS to calculate a Baro-VNAV glide path on a LOC approach. You can't mix FMS approaches and LOC ones.

Exactly, what vertical guidance is displayed in your cockpit, sir?

Denver

Circling, under Cat D, provides 550' HAA and 300' obstacle clearance MINIMUM, might be more depending on airfield.

GF

flyandive

Ok, time for me to jump in because if I'm confused then I know a few other people are as well.

There might be some confusion on what CANPA is so to clarify it stands for Constant Angle Non-Precision Approach. I'm not sure what the difference is between CANPA and "Real CANPA" is. It is a way to calculate a constant angle descent for a Non-Precision approach. Very rarely do you have to do much calculating since there is usually an approach angle published on the chart, yes even on LOC only charts and Jepps also have a descent rate table specifically for CANPA. In short CANPA is for Non-precision approaches. If you are thinking of VNAV then you are thinking of something different. Yes, some FMS VNAV approaches technically are still non-precision approaches making it a form of CANPA, it is not what most of us think of when we are talking about CANPA.

I did look at KSMX and BC is a circling only approach so it won't have a glide path angle on it because it is not an approach to a runway. You would either have to descend before the MAP and stepdowns to fly a straight in or just fly a circling approach. Every other LOC only plate I looked at though, did have a descent angle published as long as it was straight-in to a runway.

Lastly, it is possible to to have FMS VNAV on a LOC only plate depending on the equipment and the approach. I know this because I have flown aircraft with this capability and approval with a few caveats. You may have noticed on some approaches the note: "Only authorized operators may use VNAV DA(H) in lieu of MDA(H)." For those approaches the published MDA met DA criteria for obstacle clearance.
For the Q400 (The aircraft I have experience with) we would fly the approach as if it was a GPS approach using FMS data and an FMS calculated VNAV, however if it was properly loaded a "LOC" flag would come up indicating the FMS was showing the LOC CDI (Not RNAV CDI) and we would fly the approach to the MDA (Now a DA) before going missed which meant we would go below it during the missed approach. If that note was NOT there then we could fly the approach the same way performing all the CANPA calculations but we would have to add 50' to the MDA (Derived DA [DDA]) to ensure not going below it during a missed approach and the VNAV information was advisory only. This is very similar to how we fly CANPA approaches in the CRJ which only has advisory VNAV; hit the FAF fully configured, on speed, and begin a descent using the table on the jepp charts, about 7-800fpm until arriving at the DDA then go missed or land. If there is no table we calculate it like Rickair said.

galaxy flyer

Flyanddive

If it is a CANPA, how can it be flown without some means of vertical guidance? You have to use VNAV, almost always, a Baro-VNAV produced path. If not, you are just guessing as to whether the airplane is, in fact, on the "constant angle". Baro-VNAV is still a non-precision approach. Collins and Honeywell do NOT allow mixing LOC with VNAV guidance. It can be displayed, but not used. Speaking ProLine 4/21 and Honeywell 2000 in Bombardier planes.

GF

flyandive

It is a best guess, like ded-reckoning. You know the glide path angle (or it can be calculated from the altitude and the distance) and you know, or can estimate your groundspeed. Therefore you know how fast you must descend to maintain glidepath. You can check your work as you fly the approach using 300' per nm and can adjust if you are too high or too low. If understand if you are still skeptical, many are until they see it, but it does work. Most of the time though the range is pretty narrow 700-900fpm. if your approach speed is 140kts the descent rate will be about 800fpm and you can adjust as needed. If you error on the high side you can always fly a "dive and drive" profile but of the three airlines I have worked for that have taught and used this technique we were eventually prohibited from doing that. If we hit the DDA early we initiated a climb but not the missed approach. We waited until the MAP for that.

As far as the mixing you are correct in reference to the CRJ (ProLine 21?) the Q400 on the other hand (Thales with Universal FMS?) not only displays a VNAV path but you can also connect the autopilot to it through the flight director and if your airline is an approved operator you can use it if noted on the plate. So it depends on the equipment and the operator.

Denver

[QUOTE=rickair7777;1277463]FMS has nothing to do with CANPA.

I was joking.

Denver

I was referring to the SMX BC approach and I am in a Cat C aircraft. So CAT C mins show 839' HAA. So to calculate a 3 degree slope out from the TDZ would be approximately 2.4 nm final for runway 30. The circling limitation for Cat C is 1.7nm. So for a night circle in low visibility and to assure yourself of 300 feet of obstruction clearance AND staying w/n circling radii until capturing the VASI on final you would be almost as high just doing a strait in and following the profile. What I was trying to say is that you could descend early on base but you had better know where all the rock piles with your name on them are.

This is why I do not perform circling approaches at night to unfamiliar airports. With that said even doing a strait in on a dark night and not being familiar with the area and trying to be stabilized 3.0 degrees would lead to a similar scenario with a geared piston engine aircraft. Kind of a catch 22 if you have never been there before. Now in an airplane that you can perform a steeper descent in and still be stabilized it is a non issue.

cougar

There are three separate issues at play here. First, does the aircraft in question meet AC 20-129 requirements and have approval in the AFM for VNAV. If so then VNAV may be used for the final segment regardless of the type of approach(excluding RNAV approaches).

Second, does the operator have Ops Spec C073 approval per Order 8260.54 to fly VNAV to a DA in lieu of an MDA. According to the Order, an obstacle assessment must be accomplished prior to using DA in lieu of. However, it states the FAA has done an obstacle assessment on all RNAV to LNAV/VNAV minima, all ILS approaches(i.e. G/S OTS), and an approach with a VASI or PAPI. Jeppesen has coded the VASI/PAPI with the ball note "only authorized users may use DA in lieu of MDA". So with Ops Spec C073, an RNAV to LNAV/VNAV minima, ILS G/S OTS or an approach with ball note can be flown to a DA.

Finally, referencing more Advisory Circulars, specifically AC 90-105, would give operator approval for RNAV approaches. Either RNAV(GPS) or possibly RNAV(RNP) with SAAAR approval.

All this enables an operator to use VNAV to fly a constant angle non-precision approach. But as some have pointed out, you can fly a constant angle approach without VNAV path guidance. In fact, even with VNAV approval, there are some ILS G/S OTS approaches where the VNAV path will violate a step down fix. In that case, vertical speed would be used to ensure step down fix compliance, but still flying a CANPA type final segment. Most major airline operators have gone to the DA/DDA minimum only. Regardless of VNAV or V/S on the final segment, once at DA/DDA, a missed approach is executed if runway environment is not in sight.

Boeing has changed terminology as well. They label the approaches either an ILS or an Non-ILS. Non-ILS can included VOR, RNAV, LOC, IAN or GLS for example. 787 and -8 have IAN and GLS capability(I think some 73NG as well).

This has been my experience with Honeywell 757/767-200 200k FMS, 767 PIP FMS, 757/767 Pegasus, 767-400 Pegasus 2000 and the 747-400 and -8 FMS's.