OK465:

There is also a Silver ILS 16R for certain approved operators that has much lower mins. It was explained to me that if certain aircraft had good engine out performance and could do the MAP over the terrain after descending to lower mins, the Silver ILS was approved.

Interesting, too, that the FAA version of the approach has some differences, notably a 9000' PT alt and 8500* at TAKLE (*7400 when authorized by ATC).

flarepilot, I accept that in some odd cases an ILS may have higher mins than an NPA to the same runway (Bloggs, thanks for noting the slightly higher min for the CDA and how that could affect the approach, I had intentionally glossed over that because it doesn't detract from my main point.)

My main point is that you should not be altering the way you fly an approach on rare occasions in order to increase your chances of getting in. You fly the approach one way, the same way, every time, and if that doesn't get you in then you go elsewhere. The only approach worse than a dive and drive is a dive and drive by an out of practice pilot who normally does CDAs.

The ONLY time you do something different is if you have run out of options and are forced to bust minima, even then I think a CDA with lower min would be safer than a dive and drive.

OK465:
The airline I retired from has the Silver ILS available and a Southwest captain told me they have it. A corporate Challenger-flying buddy also had it some years ago.

aerocat


you should always fly an approach safely...now, once in awhile there are unique circumstances that have you modify things a bit...mind you not alot but just a bit.

you should certainly never bust minimums.

but sometimes I can see doing a dive and drive instead of constant descent...it really depends on what you expect to see near the MDA and different points along the apch


you should also never leave the safety of the MDA unless you are sure you can fly to the airport / runway visually.

How are you descending CDA when you reach altitude of a fix or MDA without stopping stabilized approach with GO A ROUND or level the flight until the next fix distance at that height?? ? So you cannot claim to only use that method without using Dive&drive technic, and not training Dive&drive NPA getting out of practice of Dive&Drive??? .:E Stabilizing the approach in short final is fine on airliners but the intermediate and final approach must manage TRANSIENT regimes.

What about a steam gauge jet airliner without VNAV? Dive and drive is the only option without some vague, pilot created method of CDA.

Aussie jet operators have been doing it since the early 80s (with a DME, of course). Work out a 3 x profile and down you go, miss all the steps no problem. Pop out just a tad below the VASI at the MDA. :ok:

Enlighten me, please. I can understand, that the adding of 50 feet is not required in the sense of a hard figure for all aircraft and all configurations, thus using the judgement of the crew how much feet they need to add in their situation or what kind of procedure they may use for go around to make sure they stay at or above MDA. If you are saying, that the MDA doesn´t need to be treated as hard altitude anymore, then please explain with reference to the definition below.

How do you make sure, that flying a CDA you are not descending through the MDA / MDH on the go around, if the visual references are not established when reaching MDA / MDH?


Some reference here: NON-PRECISION INSTRUMENT APPROACH USING CONTINUOUS
DESCENT FINAL APPROACH (CDFA) TECHNIQUES

Retired F4, there are other official documents around from EU land that address the MDA + 50 ft technique used during CDFAs; sorry but I can't put my finger on them.

That reference you quoted is the biggest load of nonsense I have read on CDFAs. Pointing the aeroplane toward the ground at 632ft/min (120KIAS) (in it's example) and hoping that 1/ you'll miss the steps and 2/you won't be 4 whites or reds on the PAPI when you pop out of the cloud is guesswork at best. It also doesn't cover how you magically arrange to be at 5.9DME already on descent so you don't have to compensate for the bunt for the final approach.

Unless you have VNAV, the only surefire way of doing CDFAs is to use a profile which should be printed on the chart. The aeroplane will then be assured of missing all the steps and be positioned correctly on the slope, not excessively high or low.

Capn Bloggs
 

The posting of the reference is not intended to lecture about how a CDA has to be done, i just used it concerning the MDA, and the last reference is directly from the ICAO website dated November 2012.

I still wait on a serious reference, where it says exactly the oposite, that you may drop below the MDA on CDA approach without having the required visual references.

Desert185 and Capn Bloggs posts give me significant concern. 185 claims to have been around long enough to know and Bloggs .is either spinning a yarn or inadequately trained. Heaven help both with FMC failure.

I don't think anybody is suggesting that you drop below the MDA on a CDA. Some authorities (including my own) have allowed CDAs to be flown with a "Derived Decision Altitude" of MDA+50. Provided you commence the GA at the DDA, it is considered that your obligations with regard to MDA are met.

The Pakistanis are onto it:
http://www.caapakistan.com.pk/format1/ASC%20016.pdf

BOAC, you should think outside the square a little. The world doesn't revolve around GMT+0.

In my last lot we could fly NDB and VOR overlay approaches to the minima on the chart, treating it as a DA, if we flew a CDFA, which in fact was mandated anyway.

That minima in most cases was the 'old' MDA and in a few cases was the 'old' MDA plus a bit but I guess the new minima was derived differently.

I can't give you a reference for it (wouldn't know where to look and can't be bothered) although it was, without doubt, written in the Ops manual and, therefore, approved by the authorities.

Capn Bloggs - I apologise -I mis-read your posts. Where did the 120kts, 'the bunt for the final approach' and 5.9D come from?

BOAC:
:yuk: :)

From the link Retired put up.

Re bunt, while the document goes into incredibly detailed lengths to calculate, to the nearest foot/min, the required descent rate, it abjectly fails to address how you compensate for the fact that the final descent will probably be started from level flight. The action lowering the nose to commence the descent (bunt) will put you at least 100ft high straight off, with no idea how high you subsequently are until you either clip a step or find yourself with 4 whites at the DDA.

Re your quip about FMC failure, it should be plainly obvious to an ace like you that the distance/altitude profile technique does not require any such wizardy. You just push a bit, pull a bit using your VSI to stay on the required profile.

thanks for teaching me something...BUNT means to lower the nose

wow...flying since before jimmy carter was president...how did I survive without knowing that one?

non precision approaches are really quite easy...descend to the MDA prior to the MAP (that's the missed approach point)...look for the runway, etc and either go visually to the runway or go around.


too much thinking can cause a crash.

No, it doesn't have to.

Look, here is how I fly an NPA. This is in a very steam driven four engined jet with no VNAV and no vertical guidance from the FMC, I can't even select a specific VS, it is easiest to hand-fly NPAs in this machine for that reason. I'll use the Adelaide VOR approach to RW05 as an example.

Note how the approach chart has a handy altitude/DME distance scale between the plan view and profile view? It effectively starts at 10nm and gives you an altitude every mile that puts you on a 3º slope to the touchdown zone and stays above all of the steps. This is the meat of this CDA approach, stay on that profile and you will have 2reds/2whites on the PAPI at the minima (or close enough to make it work from there.)

You could work out your own profile if the chart didn't provide it or you wanted easier numbers to work with.

https://lh4.googleusercontent.com/-z...9.45.06+AM.png

Now, I look at that profile and I say, for a gross error check, that after leaving 3000 feet at 10 DME and noting the limiting step at 7 DME, if I am about 3 x DME - 100 feet I am close enough to the profile. If I can I will follow the profile as written with support from the PNF but if we can't check it exactly at some point I know that 3 x DME - 100 is safe and will leave me in a good position at the MDA.

So the maths from 3000'/10 DME is already done for me. Now I have to work out how to get to 3000'/10 DME. Assuming tracking via LUNGA, I can see it is about 5 NM of arc and another 2.5 NM to the 3000/10 point. You lose a mile or two cutting the corner in the turn so I'll call it 6 track miles between LUNGA and 3000/10, at a TAS of 180 knots that will take 2 minutes. If I use a comfortable 700 fpm descent between LUNGA and 3000/10 I can see that I need to hit LUNGA at 4400 feet. I then work back from 4400'/LUNGA to find a top of descent point and make an allowance for slowing down. Note that I haven't worked out a profile for every mile around the arc or anything, that part isn't critical. It doesn't matter if I'm a little high or low at LUNGA and it doesn't matter if I'm not at exactly 3700' commencing the turn to final, what matters is that I hit the 3000'/10 point accurately and that I cross LUNGA at an altitude that allows me to hit that 3000'/10 point accurately. Something between 4000 and 5000 at LUNGA will work fine.

Now all I have to do is fly the aeroplane to hit the numbers on the approach.

I commence descent at the appropriate time and monitor the enroute descent, adjusting as necessary to hit LUNGA at about 4500 feet / 180 knots / flap 18. Descend on the arc at 700 fpm and continue slowing to 160 knots turning final. Adjusting the descent rate as required so I hit 10 DME at 3000', I continue configuring the aircraft and flying the profile aiming to be stable by 1000' at the latest.

Throughout the final approach the PNF will, workload permitting, monitor the profile and call any deviations, they will also provide the next target. E.g., "9 miles 100 high, 8 miles 2400." I will also be monitoring the profile and adjusting the vertical speed to be as close to the alt/dist profile as I can be. If I can't read the profile for some reason then I will use the 3 x DME - 100 approximate profile that I'd worked out earlier.

As a target vertical speed for the final approach I'll just use ground speed * 5 + 50. At 140 knots that gives me a VS of 750 fpm which is very close to what the chart says on the lower left.

This is the way I've flown NPAs in piston engined twins, turbo-props, and jets. It works in any aeroplane whether it has VNAV or not and doesn't involve destabilising the approach at every limiting step!

Now there are lots of ways to skin a cat, and that is only one way. I'm pretty sure Capt Bloggs would have some different ideas. For one I suspect he works for a company that likes you to work out and write down your own profile. I don't see the point and would rather use the profile on the chart. If my eyes get too old to read it, I'll re write the same profile in nice big letters. But overall, the intent is the same, fly a constant angle descent throughout the approach that keeps you above all altitude restrictions and spits you out the bottom on profile.

My pleasure. Happy to be of service to our American aviator brethren.

And too little can also cause a crash. The number of CFITs during CDFAs would be? The number of CFITs during Dives and Drive (not much thinking required) would be?