Tech Log The very best in practical technical discussion on the web

MDA

Old 24th Aug 2013, 22:27
  #81 (permalink)  
 
Join Date: Mar 2008
Location: Western USA
Posts: 556
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).
Desert185 is offline  
Old 25th Aug 2013, 12:23
  #82 (permalink)  
 
Join Date: Jan 2004
Location: Here and there
Posts: 2,741
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.
AerocatS2A is offline  
Old 25th Aug 2013, 14:26
  #83 (permalink)  
 
Join Date: Mar 2008
Location: Western USA
Posts: 556
OK465:
I also believe it was initially requested by one specific operator, but I don't know for sure what its status is now since it's not public. It's been awhile.
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.
Desert185 is offline  
Old 28th Aug 2013, 00:36
  #84 (permalink)  
 
Join Date: Aug 2013
Location: chicago
Posts: 359
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.
flarepilot is offline  
Old 28th Aug 2013, 07:24
  #85 (permalink)  
 
Join Date: Jun 2011
Location: france
Posts: 756
Originally Posted by AerocatS2A
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.
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??? . Stabilizing the approach in short final is fine on airliners but the intermediate and final approach must manage TRANSIENT regimes.

Last edited by Jetdriver; 28th Aug 2013 at 08:36.
roulishollandais is offline  
Old 28th Aug 2013, 11:53
  #86 (permalink)  
 
Join Date: Mar 2008
Location: Western USA
Posts: 556
What about a steam gauge jet airliner without VNAV? Dive and drive is the only option without some vague, pilot created method of CDA.
Desert185 is offline  
Old 28th Aug 2013, 12:22
  #87 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,746
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.
Capn Bloggs is offline  
Old 28th Aug 2013, 13:04
  #88 (permalink)  
 
Join Date: Jun 2009
Location: Germany
Age: 66
Posts: 782
john_smith
Do you understand why we are no longer required to add 50' to the MDA to create an artificial DA?
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.

Definition
The Minimum Descent Altitude (MDA) or Minimum Descent Height (MDH) is a specified altitude or height in a Non-Precision Approach or Circling Approach below which descent must not be made without the required visual reference. (ICAO Anex 6)
Note 1. MDA is referenced to mean sea level and MDH is referenced to the aerodrome elevation or to the threshold elevation if that is more than 2 m (7 ft) below the aerodrome elevation. An MDH for a circling approach is referenced to the aerodrome elevation.
Note 2. The required visual reference means that section of the visual aids or of the approach area which should have been in view for sufficient time for the pilot to have made an assessment of the aircraft position and rate of change of position, in relation to the desired flight path. In the case of a circling approach the required visual reference is the runway environment.
Note 3. For convenience when both expressions are used they may be written in the form “minimum descent altitude/height” and abbreviated “MDA/H”.

http://www.skybrary.aero/images/thum...x-101020-1.jpg

An MDA/H differs from a DA/H in that the aircraft must be flown in such a way that it does not descend below the MDA/H unless the required visual reference has been established. Typically, an aircraft will continue at the MDA/H until a pre-calculated missed approach point is reached; if the required visual reference is not established by that point a Missed Approach will be flown.
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


Decision Approaching MDA.
Flying the publishedVDA will have the aircraft intersect the plane established by the MDA at a point before the MAP. Approaching the MDA, the pilot has two choices:
continue the descent to land with required visualreferences, or
execute a missed approach, not allowing the aircraft to descend below the MDA. (See Annex, Figure 1B- ApproachExampleUsing ContinuousDescent Final Approach).

Last edited by RetiredF4; 28th Aug 2013 at 13:24.
RetiredF4 is offline  
Old 28th Aug 2013, 13:36
  #89 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,746
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 is offline  
Old 28th Aug 2013, 13:45
  #90 (permalink)  
 
Join Date: Jun 2009
Location: Germany
Age: 66
Posts: 782
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.

Last edited by RetiredF4; 28th Aug 2013 at 13:47.
RetiredF4 is offline  
Old 28th Aug 2013, 13:47
  #91 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,584
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.
BOAC is offline  
Old 28th Aug 2013, 13:59
  #92 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,746
Originally Posted by RetiredF4
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.
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.
Capn Bloggs is offline  
Old 28th Aug 2013, 13:59
  #93 (permalink)  
 
Join Date: Sep 2010
Location: England
Posts: 1,955
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.
Lord Spandex Masher is offline  
Old 28th Aug 2013, 14:39
  #94 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,584
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 is offline  
Old 28th Aug 2013, 21:05
  #95 (permalink)  
 
Join Date: Mar 2008
Location: Western USA
Posts: 556
BOAC:
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.
Desert185 is offline  
Old 28th Aug 2013, 23:33
  #96 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,746
Originally Posted by BOAC
Where did the 120kts, 'the bunt for the final approach' and 5.9D come from?
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.
Capn Bloggs is offline  
Old 29th Aug 2013, 01:13
  #97 (permalink)  
 
Join Date: Aug 2013
Location: chicago
Posts: 359
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.
flarepilot is offline  
Old 29th Aug 2013, 01:29
  #98 (permalink)  
 
Join Date: Jan 2004
Location: Here and there
Posts: 2,741
Originally Posted by roulishollandais
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??? . Stabilizing the approach in short final is fine on airliners but the intermediate and final approach must manage TRANSIENT regimes.
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.



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.
AerocatS2A is offline  
Old 29th Aug 2013, 01:47
  #99 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,746
thanks for teaching me something...BUNT means to lower the nose
My pleasure. Happy to be of service to our American aviator brethren.

too much thinking can cause a crash.
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?
Capn Bloggs is offline  
Old 29th Aug 2013, 02:20
  #100 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,746
Originally Posted by Aeroscat
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.
Not at all. We were doing this before the distance/Altitude profiles were introduced into the Australian AIP some years ago.

I now use the charted table (if the VNAV is "not available" ) although it is easier to anticipate whole 100s of feet, especially on the tape altimeter.

The only problem with the charted table is it normally only starts at the MSA, so you have the problem I alluded to above; that of getting the aeroplane into a descent prior to, so that you're not pushing the nose over at the start of the profile. I use 300ft/nm back from the start of the table to get organised.
Capn Bloggs is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.