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MDA + 50

Old 25th Oct 2017, 17:22
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MDA + 50

Flew with Flag operator who costumized NPA plates resulting in MDA renamed DA, with no change in the actual numeric value. ie. MDA 400’= DA 400’

Why are some operators required to add 50 feet when others will cross state MDA before executing a missed approach?
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Old 25th Oct 2017, 18:20
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It is regulator's requirement. All may not have it.
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Old 25th Oct 2017, 18:56
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Already discussed here http://www.pprune.org/questions/6008...-minimums.html
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Old 25th Oct 2017, 19:25
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no one crosses the MDA and then goes missed, what are you talking about?

You have to figure your momentary descent so when you go missed, you dont go below the MDA...it is a glass ceiling...Chances are, your momentary descent is more than 50 feet, so when you have an MDA, you have to calc your minima so you dont bust the MDA.

I would be very curious which operator has the MDA and DA at the same altitude.

MDA can NEVER be the same as DA.
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Old 25th Oct 2017, 20:10
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Just so I'm not confused...wouldn't it be a glass floor?
I also wouldn't be surprised at some of the arbitrary decisions made by flat ops inspectors/regulators at various CAA's around the world. Many of them have very little experience. What kind of person are they going to attract paying civil service salaries?
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Old 26th Oct 2017, 00:03
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Several VERY large operators in EU did they homework and assesment, at the end deciding that for CDFA (!) the MDA needs no add-on and momentary dip below the value poses no geometrical risk.
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Old 26th Oct 2017, 09:06
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There are some countries in which the aviation authority has made it mandatory to add 50'. There it leaves no choice.
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Old 26th Oct 2017, 10:12
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Several VERY large operators in EU did they homework and assessment, at the end deciding that for CDFA (!) the MDA needs no add-on and momentary dip below the value poses no geometrical risk.
That is exactly what our lot did, used to add 50ft but after this process the (UK) CAA have authorised us to operate using MDA as a DA.
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Old 26th Oct 2017, 10:59
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In reality this regulation is merely pedantic. By breaching 50+ you compromise a regulation but not safety. Even if you add 50ft. a lazily executed GA will loose more height. But rules are rules, take it with a pinch of salt if you have to.
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Old 26th Oct 2017, 11:41
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JEP 15-A1 31 JUL 15 BRIEFING BULLETIN

NEW POLICY CONCERNING THE GLOBAL APPLICATION OF
AERODROME OPERATING MINIMUMS (AOM) q$i

The label “Standard” on current IAPs indicates the AOM are according to EU-OPS. This label will also apply to
the new Jeppesen AOM as predicated on the ICAO AWOM.
DESCENT LIMIT LABELS (DA vs MDA)
When a State defines a Descent Limit value as either a DA or an MDA, Jeppesen will depict the label(s) as such.
Where a State does not define a Descent Limit label, Jeppesen will depict a combined label as DA/MDA. The
combined label will be used to accommodate operators who may choose or may be required to use the CDFA
flight technique.
Where Jeppesen applies a combined DA/MDA label, a note will be added to indicate that a height loss adjustment
value must be added to the charted Descent Limit Value.

HEIGHT LOSS ADJUSTMENT NOTES – APPLICABLE TO
CDFA & DA(H) MANEUVER
Wherever a State authority has clearly prescribed, provided, or otherwise specified that a Non-Precision IAP
may be flown using the CDFA flight technique, and the corresponding Descent Limit value may be flown as if it
were a DA(H), Jeppesen will assume the State-provided DA(H) value includes a Height Loss Adjustment.
IMPORTANT NOTE: Jeppesen will not add any Height Loss Adjustment to any charted DA(H) or MDA(H)
Descent Limit values unless specified by the State.
IMPORTANT NOTE: When using the CDFA flight technique and using a DA(H) in lieu of MDA(H), operators
must determine and apply an appropriate Height Loss Adjustment applicable to the aircraft, landing
configuration and/or operating requirements.
As described in the previous section covering instances where a State authority might authorize the use of
the CDFA flight technique and a DA(H) maneuver, but it cannot be determined if the State has incorporated a
Height Loss Adjustment or not, the following Ball Notes will be applied to the Descent Limit values on applicable
Non-Precision IAP approach charts.
• Anote will be added to the Straight-In landing minimums: “Use of DA(H) in lieu of MDA(H) requires height
loss adjustment.”
Some States may prescribe specific DA(H) Height Loss Adjustment procedures for use when Non-Precision
IAPs are flown using CDFA and DA(H) techniques. These situations will be noted accordingly.
• Anote will be added to the Straight-In landing minimums referencing any State-provided Height Loss Adjustment
value when using CDFA technique and DA(H) maneuver.
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Old 26th Oct 2017, 11:46
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As if Jeppesen had not done enough damage with their first bulletin 5 years ago.

Let's keep in mind what they say is their explanation of what they print in their own commercial product. Not a regulation, not required procedure - especially "has to be added".
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Old 26th Oct 2017, 15:30
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Anyone,

Didn’t the FAA have an Ops Spec for commercial operators to use the MDA as a DA without adjustment IF the underlying OIS (1:34, IIRC) had been done and found clear?
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Old 27th Oct 2017, 21:49
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Yes. OpSpec C077, I think.
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Old 30th Oct 2017, 21:59
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Didn’t the FAA have an Ops Spec for commercial operators to use the MDA as a DA without adjustment IF the underlying OIS (1:34, IIRC) had been done and found clear?
How would you know that looking at an approach plate? So you think that an operator is going to do an obstacle assessment?

The DA has the 50' momentary descent, and the MDA does not.

The 50' mom descent can be a bit of a real challenge, given that you are on final, go to DA, then decide to GA...how many seconds the decision process, seconds to push TOGA, and seconds for the ac to respond on idle thrust....just how far has a heavy descended in that scenario?

The DA/MDA has been calculated not only by obstacles in the approach, but obstacles in the missed.

There are many parameters, but as soon as you start allowing guesses, it will keep getting lower and lower....

Last edited by underfire; 30th Oct 2017 at 22:15.
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Old 30th Oct 2017, 22:55
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Originally Posted by underfire
How would you know that looking at an approach plate? So you think that an operator is going to do an obstacle assessment?
Operators are already doing obstacle assessments as part of their take-off performance. Presumably the operator or a contractor would do the work required to check whether they can use the MDA as a DA or not and then publish that information to the pilots in their manuals. If it was me it would be an all or nothing thing. If the homework shows that all company destinations and alternates can use MDA as a DA then allow it, otherwise disallow it for everywhere.
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Old 30th Oct 2017, 23:32
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Really...what dream world are you living in?

What operators are doing obstacle assessments for DEP? Are they simply using the DEP minimum profiles that assure clearance? These DEP profiles along the DEP procedures are related to a missed approach?

Ahhhh..or a contractor, so you are talking about tailored/custom procedures....

Do those same contractors provide a custom DA based on obstacles in the missed...or do you assume they use the obstacle surfaces defined for DEP?

Reading this thread, it appears that some drivers have no idea what a DA or MDA means...
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Old 31st Oct 2017, 04:42
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Operators have to assess obstacles for engine out take-off performance. Whether they do it themselves or have a contractor do it is up to them. Where I work it is done by our performance department. Given that this already happens, it is not a stretch to expect them to do something similar for DA/MDA assessments if they wish to comply with the FAA notice. We just add 50', but I see no reason to poo poo the idea that other companies might do the homework necessary to use an MDA as a DA if they decide it is worth it.
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Old 31st Oct 2017, 07:45
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We have a CAA-approved policy to use MDA as a DA but only if using CDFA. We went through a long period of confusion where sometimes we added 50’, sometimes we didn’t but after some solid technical work the Authority supported our safety case.

From a practical POV, there is a considerable difference between following a NDB needle on a dive’n’drive and a stable RNAV approach on a RNP-capable aircraft with GNSS, EGPWS, etc. All our planes are equipped for the latter.

Looking at recent incidents (Air Canada springs to mind) it’s what you do *after* MDA/DA that seems to be more of an issue. A prompt go-around does the trick whether it’s MDA or MDA+50’...
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Old 31st Oct 2017, 09:12
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The confusion came when I saw airfield charts where some had DA some had MDA. The authority decided to KISS and add 50' on all NPA approaches: if indeed that was their reasoning. Given the allowable baro-altimeter error it doesn't seem a critical issue, more a technical one.
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Old 1st Nov 2017, 08:23
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Underfire:

MDA can NEVER be the same as DA.
Wrong. "Operators conducting approaches authorised by OpSpec C073 may use MDA as a DA"

Re: OpSpec C073 VNAV IAPs Using MDA as a DA/H; AC 120-108 CDFAs.

Also:

So you think that an operator is going to do an obstacle assessment?
Yes. Read AC 120-91 Airport Obstacle Analysis, and ICAO Annex 6 5.2.8 and ATT C. Part 121 and 135 operators have to do this becaaue it is the law. There must be a reason why you don't know any of this....
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