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MDA

Old 8th Sep 2013, 09:37
  #121 (permalink)  
 
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Why using DA = MDA + 50 Ft

Originally Posted by Tom Imrich
This momentary and slight descent below MDA(H) during the transition to a missed approach is considered acceptable and is assumed to typically result in a displacement below MDA(H) of 50 ft. or less.
Adding 50 Ft to MDA to get DA is quite logic : The ILS path passes the threshold at 50 Ft assumed to allow the flare and a #Vs=0 on the ground during a kiss..

PA and NPA have not the same logic, using respectively OCS and OCH, and respectively stats and margin MFO (x mountain coefficient € [1,2]).

ILS and LSO conducted approach are true constant descend.

But CDA surfing on the top of the steps of NPA is a mixed (if not bastard) solution and adding 50 Ft to MDA to build DA is not excessive. The MFO under a CDA is not absolute but derivated.

Despite it is not the law, it is the state of art as rewritten by ALAR themselve in their golden rules : Know where you are ; Know where you should be and ; Know where the terrain and obstacles are.
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Old 8th Sep 2013, 15:39
  #122 (permalink)  
 
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Tom Imrich
While authority views on this still may vary globally, and operator's policies still widely vary, and notwithstanding obsolete criteria still in TERPS and Pans-Ops, from a scientific and safety perspective, the issue of the potential minor momentary descent slightly below MDA(H) during a properly executed G/A is completely irrelevant. Both the FAA/JAA/Industry AWO HWG recognized this now over two decades ago (e.g., Theo Van de Ven's RLD paper) as well as even FAA's signed AC120-29A, which acknowledged this situation with language such as:
“Go-Around” Transition To A Missed ApproachWhen Using a DA(H) or MDA(H).
I did a search, and was not successfull to raise some substance to your quoted message.

Instead i found AC120-108 dated 01/20/2012, which seems to be newer than your reference.

http://code7700.com/pdfs/ac_120-108_cdfa.pdf

And it contains following quote, which looks quite reasonable.

f. Derived Decision Altitude (DDA). Pilots must not descend below the MDA when executing a missed approach from a CDFA. Operators should instruct their pilots to initiate the go-around at an altitude above the MDA (sometimes referred to as a DDA) to ensure the aircraft does not descend below the published MDA. Operators conducting approaches authorized by operations specification (OpSpec) C073, IFR Approach Procedures Using Vertical Navigation (VNAV), may use MDA as a DA.
Would you please explain?

Edit: Here is the mentioned specification (OpSpec) C073
http://www.faa.gov/documentLibrary/m...208900.183.pdf

Last edited by RetiredF4; 8th Sep 2013 at 17:15.
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Old 8th Sep 2013, 15:48
  #123 (permalink)  
 
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Tom,

Incorrect. There is no assumption that you can descend below the MDA on GA.
50 feet is a figure used in the criteria as a baseline, it is up to the crew to decide if the aircraft can meet the requirements for the real-time conditions.

Momentary descent is how far the aircraft descends down the flightpath, and is based on several factors.
Crew decides to go around.
Crew initiates go around
aircraft responds to go around, and
aircraft begins to climb.

The criteria is based on this timeframe taking 7 seconds, with pilot reaction time to initiate of 2 seconds.

If the engines are at approach idle, this adventure may take longer, or many other real-time factors.
With a chart showing an MDA or even a DA, the above must be understood, as there are many aircraft that will loose more than 50 feet in this timeframe.
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Old 9th Sep 2013, 01:42
  #124 (permalink)  
 
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going below the DA during a go around from minimum
Really? (just think about that statement)
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Old 9th Sep 2013, 22:44
  #125 (permalink)  
 
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The point is that a significant proportion of NPAs are no longer constructed with an MDA. Rather, they are constructed with a DA in the same manner as a precision approach. The likelihood of going below the DA during a go around from minimum is accounted for in the drawing of the procedure.
Not in the NPA TERPS which are designed with a MDA, there is no consideration for a DA. They are adapted to be used for approved operators to use a DA in lieu of the MDA if the approach visual segment meets additional criteria, for example the same runway is served by an ILS. Of course you would fly the ILS if it was in service. Jeppesen adds this information to its charts as an added value. My main point is that on NPA procedures, TERPS does not evaluate the suitability for use of a DA in lieu of an MDA, it is a separate after the fact evaluation performed as a value add product by Jeppesen.
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Old 10th Sep 2013, 00:54
  #126 (permalink)  
 
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John,

Like I said..think about it.

going below the DA during a go around from minimum
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Old 10th Sep 2013, 01:03
  #127 (permalink)  
 
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With dive and drive you don't go below MDA because of the level flight segment. While aimind for a VDP it is possible to dip below DA on a CDA
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Old 10th Sep 2013, 04:12
  #128 (permalink)  
 
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Underfire widely misses the mark

@underfire. You are incorrect, and are at least decades behind both global criteria evolution for VNAV, as well as being inconsistent with many air carrier operator policies for using VNAV globally, who by the way entirely safely use a DA in place of an MDA on a wide variety of "Non-ILS (non xLS) approaches types. This entire subject was beaten to death decades ago in the FAA/JAA/Industry AWO HWG, ...and those discussions even led to substantially revised criteria. Only flawed provisions in some authorities outdated criteria (who perhaps do not understand either FOSA or risk analysis) still (unnecessarily) force an additive of 50 ft when using a DA in lieu of an MDA. As to "beech35"'s concern, this entire subject has nothing to do with what a commercial chart manufacturer may or may not analyze, or publish. Typically commercial chart providers publish whatever the state specifies, or that which the operator asks them to publish, as based on an approved Op-Spec or equivalent.
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Old 10th Sep 2013, 07:21
  #129 (permalink)  
 
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@Tom Immrich

Do you agree ( as i'm sur that you know) that not all MDA 's of the multitudes of approaches can be converted to an DA without adding some aircraft performance dependent safety margin, and that not all operators are qualified to do so and not all air transport aircraft are equipped to do so.?
Some people here (and i'm afraid to say you as well) are making others believe that anybody in any airplane at any place can use the MDA of an NPA approach as an DA and thus being allowed to drop below the DA on go around, when commencing this NPA approach doing a CDA and thus behaviour being wise and legal.

It would be wiser in the sense of safety to publish the provisions to be made and the regulations implemented as well as the prerequisites the aircraft, the approach and the operator has to fullfill to make the use of the MDA as a DA not only legal but also wise in the sense of safety.
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Old 10th Sep 2013, 13:46
  #130 (permalink)  
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Originally Posted by John Smith
I'm at a loss as to what you think your point is.
- you are not alone.

RF4 - yes, I'm getting the same message, undoing years of understanding.
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Old 10th Sep 2013, 15:42
  #131 (permalink)  
 
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you said "going below the DA during a go around from minimum"
okay, when I said think about it, here is what I meant. How do you go below the DA, during a go around from minimum? You are confusing DA with MDA...they are not the same.

There are many operators around the world that add 100 feet to the MDA for their decision point to go around. 50 feet is the minimum, not the maximum, you should certainly consider using more depending on conditions and your aircraft.

Even with a DA, the operator must understand that the momentary descent is 50 feet, and must adjust if they need more.

The MDA is a glass ceiling that you cannot bust if you plan to go around. It is up to the individual operator, using real time conditions, to determine what add to the MDA to successfully perform the go around without breaking the glass.

Last edited by underfire; 10th Sep 2013 at 15:46.
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Old 10th Sep 2013, 17:36
  #132 (permalink)  
 
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I'm sure the use of the word 'minimums' was because that's what the aircraft says when you reach DA.
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Old 12th Sep 2013, 00:39
  #133 (permalink)  
 
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Folks,
Australia always has to be different.
Here, the AIP requires the pilot to apply an aircraft specific position error correction to a published DA, or if the figure for the aeroplane is not known, add 50' to the DA ----- in addition/subtraction to any other corrections to the approach minima ---- low temperatures etc.

Unfortunately, CASA Flying Operations Inspector training is decades out of date, so, if an exercise is being conducted under FOI supervision, operators will add another 50' so that the aircraft never indicates an altitude below the DA during a missed approach.

Procedure design rules, as per current, are a complete mystery to said FOIs.

Last edited by LeadSled; 12th Sep 2013 at 00:41.
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Old 12th Sep 2013, 06:00
  #134 (permalink)  
 
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Originally Posted by Ledsled
Australia always has to be different.
You really do have a chip on your shoulder, don't you? How about sticking up for the fact that Australia was one of the first to introduce Distance/Altitude tables on it's NPA charts, drastically improving the safety of these types of approaches?
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Old 12th Sep 2013, 07:21
  #135 (permalink)  
 
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Bloggs,

Actually, if you were to be a little more accurate (if you even know), the Qantas I worked for introduced DME based NPA AND PA approach profiles on its company tailored Jepp. charts long before the tables, to which I assume you refer. I believe I can justly claim to have played a small part in that effort ---- right back to the late 1960s.

Jepp. also produced other specific charts to our specification to assist pilots monitoring radar vectors descent clearances in areas where there was a long history of scrap aluminium scattered around the local hills. A very comforting innovation.

Think Manila, Bali and Tehran, to name several that come to mind.

If you had the wit to understand, it is nothing to do with chips on shoulders, and everything to do with a well developed Australia propensity to re-invent the wheel, and wind up with said wheel having five corners.

For foreign crews operating in and out of Australia, just trying to understand all the ICAO differences listed for Australia in the Jepp WW Text (or whatever flight deck documentation they carry), all operationally meaningless from a safety point of view, are examples of "Australia does it differently". Why?? Because they can. ICAO harmonization, wots that???

The latest scandal is the "proposed" joint civil/military ATC system, a grand reinvention of the five sided wheel, AUD$50M spent over four years to get to the stage of calling for expressions of interest --- preliminary tenders. The initial proposal has been knocking around for about 15 years from the time of the first Ministerial level agreement. Glacial?? it only took five years or so to fight WWII !!!

Whether you like it or not (the statistics are clear), Australia does not have a very good safety record, and we should look at why, having discarded our "Made in Australia" rose coloured glasses.

Australian regulatory standards are a mess, perhaps even you understand that, the relevant Senate Standing Committee does, several ICAO and FAA audits have illustrated comprehensively Australia's problems.

The most telling commentary on the real FAA view (very undiplomatic) comes from diplomatic cables from the US Embassy in Canberra, thanks to Wiki-leaks.

Possibly even you can understand what a commercial disaster awaits the Qantas group and Virgin if Australia downgraded from Cat.1 ---- just for starters they have to drop all code shares with US carriers.

Given you long history of assertions generally justifying what I, and most of my foreign going peers, regard as totally unnecessary, it is a pity you apparently have little real experience outside Australia.

If you had such experience you might understand why Australia is out of step with the rest of the aviation world.

You might even ask yourself why near neighbors who previously used rules sets based on Australia aviation legislation have abandoned that format, and adopted the NZ approach. Even the new Canadian rules (and the old ones weren't bad) will look awfully like the NZ rules.

You might even ask yourself why Australia is out of the MRO business now, unless the Australian company has EASA and/or FAA certification, because Australian release certificates are no longer recognized as coming from a system with adequate standards.

I could go on and on, and it is nothing to do with chips on shoulders, and everything to do with the steady destruction of large segments of the Australian aviation industry ----- and the fundamental reason why this is happening, compared to, say, the relative robust health of the whole NZ aviation sector.

Open your eyes!!
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Old 12th Sep 2013, 07:44
  #136 (permalink)  
 
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Originally Posted by Leedsleed
Jepp WW Text
That would be similar to the the next to useless American 2000-odd page Australian Airway Manual that doesn't have change bars? No wonder your beloved foreign operators have trouble.

At least the Australian AIP has change bars to highlight changes.

You may rightfully take credit for the being part of the development of the Distance/Altitude table. But that wasn't my point. Publicly available Australian charts had it well before others.
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Old 12th Sep 2013, 14:59
  #137 (permalink)  
 
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next to useless American 2000-odd page Australian Airway Manual that doesn't have change bars?
Bloggs,
And what manual are you referring to, please?? Produced by who, and for whom??

No wonder your beloved foreign operators have trouble.
And what trouble would you be referring to??
Beloved hardly.
It is just that I recognise (as do so many others) that the US (not just "foreign) system produces the best air safety outcomes, within a system that is not tied in knots by every waking moment of a pilots life being governed by an increasingly vast and increasingly prescriptive "strict liability criminal offence" framework, that does not have anything to do with risk minimization, and the FAA system does it all without destroying business after business, with large slabs of the GA sector on the verge of collapse, as is the case in Australia.

Your all too typical Australian prejudices are showing.
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Old 12th Sep 2013, 23:18
  #138 (permalink)  
 
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‘Safer’ is a somewhat meaningless term.
OK465,
Well said, a meaningless term, a expression without dimension. An emotive term of no use to us, but a very effective term to get the attention of the public and politicians.

We can measure risk, and to use a hackneyed phrase, "if you can measure it, you can manage it".

The construction of the obstacle clearance envelopes in Doc. 8168, and the lower minima possible, compared with earlier PANS-OPS editions, all have a risk analysis foundation, not "safe or not safe" as a design criteria.

From the accident record, it is clear that dive and drive is a serious issue, so a constant descent path decreases the risk of a CFIT and has the bonus of being a stable approach, without question (although some probably will) much preferred in any aircraft, but particularly heavy transport aircraft.

There is no such thing as "safe", only risk minimization, in one form of analysis defining a range of risk levels, titled ALARP -- As Low As Reasonably Practical.
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Old 13th Sep 2013, 12:12
  #139 (permalink)  
 
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Piloting transient path

Originally Posted by LeadSled
[We can measure risk, and to use a hackneyed phrase, "if you can measure it, you can manage it".

The construction of the obstacle clearance envelopes in Doc. 8168, and the lower minima possible, compared with earlier PANS-OPS editions, all have a risk analysis foundation, not "safe or not safe" as a design criteria.

From the accident record, it is clear that dive and drive is a serious issue, so a constant descent path decreases the risk of a CFIT and has the bonus of being a stable approach, without question (although some probably will) much preferred in any aircraft, but particularly heavy transport aircraft.

There is no such thing as "safe", only risk minimization, in one form of analysis defining a range of risk levels, titled ALARP -- As Low As Reasonably Practical.
You cannot avoid that at some moment that natural, direct idea is popping up in the approaching pilot's mind : which will the minimum probable distance to the ground be the next minute.
D&D brings the immediate answer : margin x K€[1,2].

CDA does NOT bring an immediate answer.

It is a derivate data like these computing engineers like to put in their algorithms : SS position, autotrim position, etc because you decrease the time delays and the computer compute that very easily.

The pilot's brain gets able to do it too if you teach him TRANSIENT piloting with AEOBATICS. Hand flying gets brain flying.

If you do not train aerobatics>transient piloting the mind is late and far behind the system and the CDA path : the pilot is no more able to answer easily to that question : am I ground safe? The pilot is no more able to measure the risk, and he is going very stable and comfortabily to the death under the limit.
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