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MDA

Old 27th Jul 2011, 12:13
  #41 (permalink)  
 
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alphacentauri

You could argue the same point with an ILS approach. Work those same numbers with a Cat II.
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Old 27th Jul 2011, 13:27
  #42 (permalink)  
 
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Yes, but the concept of protection on an ILS is different than for an NPA. There is no such thing as a minimum obstacle clearance for an ILS, rather a set of surfaces to which obstacles are not allowed to penetrate. If they do penetrate then you derive a DA from the penetration. This is where lack of understanding from a procedure design point of view is leading people to the false conception that an MDA can be used as a DA, they are two totally different concepts, based around two different types of approach design criteria

If you go around on a CAT II, especially below 161ft it is widely accepted that your wheels may touch the ground. Would you like to do that off an NPA to an aerodrome with no HIALS?
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Old 27th Jul 2011, 14:34
  #43 (permalink)  
 
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Its not the the airplane touching the runway that i worry about. It is when you hit something else that it becomes a problem.
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Old 27th Jul 2011, 15:06
  #44 (permalink)  
 
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Alpha,

Well stated, this coupled with the condition of most State's obstacle databases...

I am wondering what 757 is using for vertical guidance? If it is baro-vnav, lower temperatures will get you down to a 2.5 degree GPA , thats 260 feet low at the FAF, and you dont even know it.
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Old 27th Jul 2011, 15:18
  #45 (permalink)  
 
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That's the whole concept of an ILS - that is so precise that you will not hit anything but the runway.

Hence, the reason that you have to make a go around is that you don't have visual reference to make the flare and the roll out. With CAT2/3 ground equipment, it's so precise that it's acceptable that that you touch the runway during the go around as well.

Assuming of course you made a stabilized approach and made the go around due lack of contact. Making a go around at CAT2 min with full scale deflections is maybe not such a good idea.
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Old 27th Jul 2011, 15:32
  #46 (permalink)  
 
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Here is Boeing take on the matter by the way:

When specifically authorize by the appropriate regulatory authority, approaches may be flown to the following minima:
• a published VNAV DA(H)
a published MDA(H) used as a decision altitude.
When either of the above minima are not specifically authorized, use the MDA(H) specified for the instrument procedure.

Note: If using an MDA(H), initiating a missed approach approximately 50 feet above MDA(H) may be necessary to avoid descending below the MDA(H) during the missed approach, if required for the procedure or by the regulatory authority.
So where do I see on my chart if the appropriate regulatory authority allows, me to descend below MDA(H) or not??
For my part this is only if the minimum is listed as a DA on the chart.
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Old 27th Jul 2011, 15:37
  #47 (permalink)  
 
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The ILS is assumed to have a 200 foot ROC....that is the surface we use for obstacle penetration, the 34:1 surface is the visual surface for obstacles...
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Old 27th Jul 2011, 16:05
  #48 (permalink)  
 
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Cosmo

In the FAA, authorization to use DAs is a OpSpec under HBAT 99-08, so it won't be on a chart, but the company manual. This probably has been updated, but FAA authorizations are based on it. And, it must be a commercial operator under FAR 121, 125, or 135.
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Old 27th Jul 2011, 16:28
  #49 (permalink)  
 
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GF,
I am in Europe. But for the sake of the argument, let's take USA. You fly from Miami to somewhere in Bogota. How can the FAA allow you to go below minimum during a go around in another country?

The same for EU, all fine and well within EU OPS states, but what about when I fly to e.g. the middle east?

There is a big world outside US and EU.
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Old 27th Jul 2011, 21:51
  #50 (permalink)  
 
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That's the whole concept of an ILS - that is so precise that you will not hit anything but the runway.

Not true. A Cat II ILS requires a visual segment to ensure you are at the runway. For the more precise CAT III B with no DH is one of the options.

It is possible that the A/C will miss the landing area when doing CAT II hence the requirement for a visual segment.
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Old 27th Jul 2011, 22:09
  #51 (permalink)  
 
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Even when it is precise (or accurate, which would be more useful ) there is also the issue of reliability, which with the lower systems requirements for the less accurate options also leads to a need for pilot involvement.
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Old 28th Jul 2011, 00:17
  #52 (permalink)  
 
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Cosmo,

Didn't say the FAA could, it is true only in the US
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Old 18th Aug 2011, 03:50
  #53 (permalink)  
 
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I'm lost

Think I'll divert - this is getting too complicated for mortals like me!
Fireflybob...i'll join you...its really too complicated now..

Go Around Flaps !
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Old 18th Aug 2011, 16:57
  #54 (permalink)  
 
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This was posted by JimL over in the rotorheads forum, but is very applicable here...

Safety Reminder Message from Eurocontrol (dtd. 03/02/2010):


SYNOPSIS

 EUROCONTROL has been advised of concerns about the use of Decision Altitude/Height (DA(H)) instead of Minimum Descent Altitude (MDA(H)) as the aerodrome operating minima (AOM) on some non-precision approach charts produced by Jeppesen for countries applying “EU Ops”. This has become a source of confusion and has implications for aircraft operators.

ANALYSIS

 Commission Regulation EC 859/2008 dated 20 August 2008, EU Ops 1.430(d) 2 (applicable from 16 July 2011) states that “all non-precision approaches shall be flown using the continuous descent final approaches (CDFA) technique”.

 EU Ops, 1.435.9 defines CDFA as, “A specific technique for flying the final-approach segment of a non-precision instrument approach procedure as a continuous descent, without level-off from an altitude/height at or above the Final Approach Fix altitude/height to a point approximately 15m (50ft) above the landing runway threshold or the point where the flare manoeuvre should begin for the type of aircraft shown”. Moreover, Appendix 1 (New) to OPS 1.430, states that, “the missed approach, after an approach has been flown using the CDFA technique, shall be executed when reaching the decision altitude (height…”.

Note: Additional CDFA guidance material is currently under preparation.

 Jeppesen only publish DA(H) on CDFA-based, non-precision approaches where the equivalent national AIP minima is shown as an OCA(H). Where national AIP minima is shown as a MDA(H) or for non-CDFA-based, non-precision approaches, Jeppesen continues to publish MDA(H).

 ICAO PANS OPS definitions:

 Minimum Descent Altitude/Height (MDA(H)): “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”.

 Decision Altitude/Height (DA(H)): “a specified altitude/height in a precision approach or approach with vertical guidance at which a missed approach must be initiated if the required visual reference to continue the approach has not been established”.

 Obstacle Clearance Altitude/Height (OCA(H)): “The lowest altitude or the lowest height above the elevation of the relevant runway threshold or the aerodrome elevation as applicable, used in establishing compliance with appropriate obstacle clearance criteria”.

 The DA(H) value shown on the Jeppesen charts is at least equal to the published national AIP OCA(H)) minima for a non-precision approach. Importantly, however, the DA(H) published on the Jeppesen charts does not include any add-on to account for any height loss during the initiation of a missed approach. This is not mentioned directly on the charts, but it is described in the Jeppesen Briefing Bulletin JEP 08-D and in the legend pages to the Jeppesen Airway Manual.

 EU Ops 1.430 (a)1 states that, “an operator shall establish, for each aerodrome planned to be used, aerodrome operating minima…”

YOUR ATTENTION IS REQUIRED

 Aircraft operators are invited to:

 Note the issue above specifically with a review of the need to consider the requirement for an add-on factor to account for height loss at missed approach initiation.

 Share their operational experiences.

 It is critical to flight safety that pilots brief the DA(H) or MDA(H) (as appropriate) so that there is no ambiguity as to what minimums are being used irrespective of the type of approach being flown.

FURTHER READING

 Commission Regulation EC 589/2008 (EU Ops) dated 20 August 2008. SKYbrary - EU-OPS

 ICAO Doc - 8168 PANS OPS

 Jeppesen Airway Manual

 Jeppesen Briefing Bulletin JEP 08-D - 26 Sep 08 at http://www.jeppesen.com/main/corpora...b_jep_08_D.pdf

 Draft Implementing Rule for Air Operations of Community Operators (EASA NPA 2009-02B) (CDFA Guidance pages 155-165). EASA - European Aviation Safety Agency

For more information contact, EUROCONTROL Safety Alerts Coordinator, Richard Lawrence at: [email protected]urocontrol.int
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Old 21st Aug 2013, 23:28
  #55 (permalink)  
 
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I am reading this thread as a result of studying non-precision approach practices, because of the UPS BHM accident in Aug, 2013, where they hit obstacles after descending visually below the MDA to attempt to land.

Any my US -121 airline, for a non-precision approach (which we normally fly a CDMA), if there is a published glidepath on the approach chart (jeppesen) and a published glidepath in our FMS database, we are to set the MDA as the DA. Consequently, when going around we will go below the MDA.

If there is NOT a published glidepath, then we must add 50' to the MDA, which should keep up as above the MDA if we go around.
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Old 22nd Aug 2013, 03:57
  #56 (permalink)  
 
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In many countries the DCA has made mandatory to add 50ft.
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Old 22nd Aug 2013, 04:16
  #57 (permalink)  
 
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we always round up to the next 100 for the mda. mainly for the altitude alerter once we leave the mda with a visual on the runway the alerter is set to missed approach alt

and while the constant rate of descent is preferred, we sometimes use the so called dive and drive if we want to get in.
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Old 22nd Aug 2013, 10:30
  #58 (permalink)  
 
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Are there ever times when you DON'T want to get in? What's the point of flying an approach differently depending on whether you really want to get in or not? Shouldn't you fly the approaches the same way every time? After all they are not there for fun, if you are doing the approach you presumably would like to land off it.
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Old 22nd Aug 2013, 11:19
  #59 (permalink)  
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we sometimes use the so called dive and drive if we want to get in
- I think, Aerocat, we should draw a discrete veil over that post.
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Old 22nd Aug 2013, 19:21
  #60 (permalink)  
 
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Gentleman, i'm shocked.
Has the house of flight safety declined to a wh*re house, where everybody is doing what suits himself?

The definition of an MDA / MDH has not changed, not as far as i know, how come it is handled differently than before?
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