MDA

[dartman2]

Apologies if this has been discussed before.

Does anybody out there believe that it is permissible to go below MDA when not visual and conducting a missed approach from a NPA?

I am aware that many operators add an amount (around 50') to the published MDA and treat it as a DH. In this case the aircraft will not go below the actual MDA.

I am also aware of at least one operator that states in its ops manual that you can initiate the missed approach at MDA. This clearly results in the aircraft going below it.

Just to clarify this question relates only to a "traditional" NPA not a LNAV/VNAV approach with a DA published.

An authoritative reference showing the acceptability of this practice would be appreciated.

[zonnair]

A traditional NPA (some of them still have that option) has a step down procedure. In this case you level off and continue to the MAP, where you decide to go around or not. In this case you would not loose ALT, so you won't go below your MDA. With these CDAs of nowadays it gives you the possibility to shoot a NPA faster, easier and with less noise. Only problem is, that you will not level of towards the MAP. When you initiate the go around you will indeed go below the MDA.

As it stands for MINIMUM DECENT ALT, you can not bust it unless you continue with the approach. The 50' is a safe buffer.

[fireflybob]

When you initiate the go around you will indeed go below the MDA.

Well you shouldn't! The aircraft "allowance" (in the case of a continuous descent approach) should be added to the MDA - if not visual at this altitude then you go around.

If you procedures are such that you intend to fly level to the MAP you also should not descend below MDA without the required visual reference.

This has previously been extensively discussed on Pprune - suggest you do a search!

[zonnair]

That's why the 50' bobby. Read before you reply!

[fireflybob]

zonnair, yes apologies - you did say that - it's all down to semantics - have a great day.

Believe the a/c allowance depends on a/c type also.

[Lord Spandex Masher]

A recent change has allowed operators to remove, or not add, the 50' buffer if carrying out a continuous decent final approach on a NPA.

[Checkboard]

I have flown for airlines that didn't specify 50' addition for a constant descent approach.

The MDA is the MDA, and the tolerance specified was +100', and -0' ... it was left up to the pilot's skill to meet that tolerance, rather than specify any particular figure.

[despegue]

MDA on NPA's is slowly being replaced by DA at a lot of EASA member-state airports, sometimes resulting in slightly higher minima's.

In some cases, 50' makes the difference of becoming visual or doing a G/A. This is why I am not a fan of VNAV NPA approaches combined with an MDA in marginal weather. Use the V/S and put the MDA in the MCP. Keep slightly low in order to ensure level flight at the Decision Point. (Decision Point is the point where on a normal ILS, you would end up at minima considering a standard glide angle of 3°). If no contact, go around. (and NO there is NO requirement to fly level up to the MDA, this is a big misunderstanding by some collegues).
HOWEVER, and this I must emphasise: FOLLOW your COMPANY SOP. This is a personal note and in my present company VNAV NPA's are not done.

[Colin Oskopi]

MDA means Minimum Descent Altitude. You cannot descend below this altitude unless adequate visual reference is achieved.

DA means Decision Altitude. This is the altitude that the decision is made to go around. You will descend slightly below this altitude in a go around.

In my company, when conducting a NPA there is an auto call-out of "Hundred above" when there is 100 feet to go to the MDA. We count to two seconds and if not visual, push the thrust levers forward and go around. From the call of "Hundred above" and two seconds thereafter, we ensure that at no time we descend below the MDA.

[BOAC]

Keep slightly low in order to ensure level flight at the Decision Point. (Decision Point is the point where on a normal ILS, you would end up at minima considering a standard glide angle of 3°). If no contact, go around. (and NO there is NO requirement to fly level up to the MDA,- ?? Can you clarify what you are saying??

[FlightPathOBN]

On charts, the movement is towards MDA for non-precision approaches, DA for precision approaches.

You have to add your momentary descent to the MDA to get your DA.

When you initiate the go around you will indeed go below the MDA.

No you do not, never....

[Denti]

Actually MDA is the "old fashioned" way and there is a movement towards DA for all approaches including NPAs. As far as i know it is even a requirement in EASA-land to convert to DA for NPAs.

[FlightPathOBN]

If you note the Jeppeson charts, many have just recently been converted to an MDA. ICAO RNP 9905 uses MDA, while FAA 8260.52 uses a DA.
It is not due to precision, but multi-variant performance considerations. With RNP baro-vnav, the approach can be anywhere from 2.5 to 3.1 degrees on a 3 degree approach, hence an MDA...

RNP transition to GBAS final, uses of course, a DA.

[airbus757]

When conducting approach other than ILS, there is no need to add 50ft to MDA as long as a CDA is being used. This is relatively new proc at my current company. We were doing it 15 years ago at my previous company.

7

[FlightPathOBN]

What do you mean there is no need to add 50 ft to MDA?

If the MDA is 650, what is your DA min?

[airbus757]

With an approach MDA of 650 we set 650. This means that the A/C will dip below MDA if a missed approach is flown.

7

[FlightPathOBN]

That is completely wrong. You can not go below the MDA on a missed approach.

SKYbrary - Minimum Descent Altitude/Height (http://www.skybrary.aero/index.php/Minimum_Descent_Altitude/Height)

[airbus757]

I assure you that it is sop at our airline. It is in black and white in our OMA.

7

[FlightPathOBN]

Sorry to hear about that, but you are violating the rules of you descend below the MDA on the missed approach.
You have no assurance of obstacle/terrain clearances.

[Lord Spandex Masher]

Nope, they're not. EU-OPS says so.

A fairly recent change, like us, allows it only if your are carrying out a CDFA. The actual plates show a DA(H) as opposed to MDA(H).

[hawker750]

FlightPath is correct ,not allowed below MDA. If the chart has been constructed to show a DA then it should have an allowance so as not to go below MDA in the event of a GA

[FlightPathOBN]

The plates shows DA if it is a precision approach. Non-precision approach shows MDA. DA assumes a 50 foot momentary descent, if yours is greater, than you must adjust your min.

If the plate shows MDA, you cannot go below that for a missed approach.

[airbus757]

I am 100% confident that we are not breaking the rules. This is clearly laid out in our SOP. I work for one of the largest airlines in the world and am sure that such a policy would not exist if there was any doubt as to its legality.

In fact we do have assurance of obstacle/terrain clearance in the same way we have clearance when conducting ILS approaches.

I can see that you and others here are highly qualified and have much to offer to the community. I respect you. Please extend me the same courtesy.

We are not violating the rules. The combined total experience in our airline is somewhere on the area of 42,000,000 flight hours. Trust me we have the issue covered.

[FlightPathOBN]

I am just as equally certain that you cannot go below the MDA on a missed approach.

This is a very common misconception regarding MDA.

Why have an MDA if you can go below it?

[Lord Spandex Masher]

That's the point. Our, specific, charts show all NPA's with a DA(H).

So, therefore, we do not need to add 50' to the nonexistant MDA(H)


Para (b)(2). The use of the MDH as a DH is introduced as a consequence of the prohibition of level flight at MDH (or multiple step-downs during non-precision approaches) when using the CDFA technique.

[FlightPathOBN]

That is not the point, this was the post I was responding to...

With an approach MDA of 650 we set 650. This means that the A/C will dip below MDA if a missed approach is flown.

MDA not DA

[Lord Spandex Masher]

Keep up at the back!

CDFA has been mandated by EU-OPS and, therefore, the requirement for an MDA has been removed.

If you can't or don't currently fly a CDFA there is, I believe, a three year transition period but at the end of that time you will be expected to use CDFAs on every NPA. That will remove your requirement for an MDA and you will be flying to a DA(H).

It's not an MDA anymore, it is a DA. It doesn't matter if you go below it carrying out a go around.

Have you heard of "Lower Than Standard" and "Other Than CAT 2" approach ops? That means that I can fly an ILS to a minima below the conventional limit. That means I can fly a CAT 1 ILS in 400m RVR instead of 550m. But I suppose it's wrong to do that too.

It's all part of EU OPS Subpart E. Have a look!

[FlightPathOBN]

I design procedures, including RNP to GBAS finals that have no minimums.

Of course there are DA approaches, but what happens if there is no ILS? Its an MDA approach.

The question was specific to MDA, not DA, and I gave a specific answer.

[Lord Spandex Masher]

If there's no ILS you fly a NPA with a CDFA to a DA.

Whether that DA is now the old MDA or the old MDA+50' depends on how the minima is derived, not my department but...every NPA that I do, daily, has used the old MDA figure as a DA, in accordance with current regulations.

[fireflybob]

Think I'll divert - this is getting too complicated for mortals like me!

[FlightPathOBN]

If you used the MDA as a DA, then it was wrong. If the MDA stated 650, and you used 650 as the DA for a NPA, it was wrong.

Also, currently ICAO 9905 RNP procedures are non-precision,
and the RNP procedures use CDA to an MDA...

[Lord Spandex Masher]

Sorry OBN but that is simply not the case.

From the horses mouth - Subpart E:

Para (b)(2). The use of the MDH as a DH is introduced as a consequence of the prohibition of level flight at MDH (or multiple step-downs during non-precision approaches) when using the CDFA technique.

[FlightPathOBN]

Perhaps rather than cut/paste a quite, you should go to the document.

The ref you make is an explanation of the terminology where MDH as a DH is used. (note introduced)This was to harmonize with the FAA and now DA is DH....
However, this is the MDH and DH, which is in the process of being transitioned to. This MDH/DH is a DA, but it is NOT the MDA.

The DA or DH take into account the momentary descent for the CAT aircraft, MDA does not.

page 254/57
SUBPART E
ALL WEATHER OPERATIONS
OPS 1.430
Aerodrome operating minima — General


note in the minima Tables...

Note 7: The MDH mentioned in Table 4a, 4b, 4c and 4d refers to the initial calculation of MDH. When selecting the associated RVR, there is no need to take account of a rounding up to the nearest ten feet, which may be done for operational purposes, e.g. conversion to MDA.



http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:254:0001:0238:EN:PDF

[FlightPathOBN]

JAA document NPA-OPS 41

While this is paraphrasing, this MDA vs DA is of concern....

The application of the CDFA technique requires all NPA operations, to be flown with a decision altitude/height (DA/H). When determining the applicable DA/H, the operator must take account of the missed approach point (MAPt) and the minimum descent altitude/height (MDA/H). While it is quite clear that a missed approach must be initiated not later than at the MAPt, the question of MDA/H is a different matter. Quite a few operators use MDA/H as the DA/H with no height add-on; in fact this is the case with a majority of the largest European operators. This modus operandi has raised concern that the unavoidable height loss below the MDA/H during a go-around might introduce a safety risk, even if the height loss can be minimised by the use of appropriate operational procedures (call-outs, high degree of on-speed/on-path discipline, training)


The matter of using the MDA/H as a DA/H is progressing in the ICAO OCP and OPSP. Until there exists a final result of the work in ICAO, it must be left to the discretion of each Authority to make decisions on the matter. Since the benefits of the CDFA technique are generally acknowledged, the decision is typically whether to require an add-on to the MDA/H to ensure that the height loss does not lead to flight below the related MDA/H during a go-around, based on formal or other reasons.


http://www.jaa.nl/publications/npas/NPA-OPS%2041.pdf

[Lord Spandex Masher]

OBN, that document you quote from is over four years old. However, Subpart E has now incorporated some of the proposals.

You seem to have conveniently missed this bit.

Issues related to DA/H and MDA/H
The application of the CDFA technique requires all NPA operations, to be flown with a decision altitude/height (DA/H). When determining the applicable DA/H, the operator must take account of the missed approach point (MAPt) and the minimum descent altitude/height (MDA/H).

While it is quite clear that a missed approach must be initiated not later than at the MAPt, the question of MDA/H is a different matter. Quite a few operators use MDA/H as the DA/H with no height add-on; in fact this is the case with a majority of the largest European operators. This modus operandi has raised concern that the unavoidable height loss below the MDA/H during a go-around might introduce a safety risk, even if the height loss can be minimised by the use of appropriate operational procedures (call-outs, high degree of on-speed/on-path discipline, training). In order to evaluate the safety of the use of MDA/H as DA/H, the AWOSG has compared the obstacle protection for this type of approach with the obstacle protection for ‘traditionally’ flown non-precision approaches as well as with the protection for approaches with vertical guidance (APV) using the criteria contained within ICAO PANS OPS.

The AWOSG is convinced that using the MDA/H as a DA/H offers adequate obstacle protection.

Another comparison between the CDFA technique and the ‘traditionally’ flown non-precision approaches indicates that the latter involve several safety traps,
such as:
• Early descent with a prolonged flight close to obstacles;
• Multiple step-downs possibly inside the FAF;
• An approach which is, by definition, destabilised;
• Temptation to make a late and steep descent from MDA/H towards the threshold;
• Risk of descending early from the MDA/H;

While there are no records of accidents related to the use of the CDFA technique during approach operations, there are several accidents attributable to the risks listed above.

That is what has been implemented and that is how we operate, perfectly safely and legally. In fact they have proved that CDFA using MDA as a DA is safer than the traditional NPA even with the 50' buffer!

The DA(H) figure is derived from the OCA(H) for the associated procedure plus any buffer decided by the operator or the authority. MDA(H) is the lowest altitude (height) for the level portion of an approach flown using the traditional dive-and-drive technique, not the CDFA technique. Use of MDA(H) would undermine the philosophy of the CDFA

Use of the CDFA technique is considered as a significant safety improvement. (Ref to ALARP). It is also important to note that the NPA does not suggest anything that is not already in widespread use by European operators

[FlightPathOBN]

The "4 year old document" is where your quote Para (b)(2). The use of the MDH as a DH is introduced as a consequence of the prohibition of level flight at MDH (or multiple step-downs during non-precision approaches) when using the CDFA technique.came from.


I agree that it has been incorporated, in ways that you may not understand. I also understand that the calculations associated with determination of MDH have been revised to account for momentary descent given the propensity for "Quite a few operators use MDA/H as the DA/H with no height add-on; in fact this is the case with a majority of the largest European operators."

"The DA(H) figure is derived from the OCA(H) for the associated procedure plus any buffer decided by the operator or the authority. MDA(H) is the lowest altitude (height) for the level portion of an approach flown using the traditional dive-and-drive technique, not the CDFA technique. Use of MDA(H) would undermine the philosophy of the CDFA"

Just how do you think we calculate Obstacle Clearance?

And I will let you guess...."plus any buffer decided by the operator or the authority." what that buffer is.

dont worry, we have you covered...

check out this thread...http://www.pprune.org/tech-log/457743-missed-approach-climb-gradient-question-3.html#post6597656

[Lord Spandex Masher]

Actually you're wrong, my quote came from the EU OPS document which is currently in use, right now, based on the proposals in the document that you quoted from.

MDA(H) is the lowest altitude (height) for the level portion of an approach flown using the traditional dive-and-drive technique

We do not fly level, we use CDFA.

I know I'm repeating myself, again but what don't you understand about this?
The AWOSG is convinced that using the MDA/H as a DA/H offers adequate obstacle protection.
Use of the CDFA technique is considered as a significant safety improvement.

My operator and the authority that I operate under do not require us to add on a buffer.

For example, at an airport I used to frequent.

VOR/DME approach with an MDA of 530'. We used to have a DA of 580', 50' buffer you see.

We now operate the very same approach, completely legally, to a DA of 530' using a CDFA.

I have yet to be charged with flying illegally or dangerously. Even though I once flew that approach to that minima with a CAA inspector on the jumpseat.

End of story.

[FlightPathOBN]

I understand the issues completely, and may have designed many of the procedures you may be using.

As noted, even if the AWOSG is convinced using the MDA without a momentary descent is okay....
Unfortunately, the criteria and procedure design parameters do not support this. (if there is an event, good luck, as I am sure that when your operation decided to use the MDA as a DA, you did a re-evaluation of the terrain and obstacles to support this decision)
Precision and non-precision approaches have a base terrain and obstacle evaluation, that assume the controlling obstacle, add the ROC, and that is how the MDA is calculated, but what you fail to realize, is that the areas that are evaluated are very small considering the procedures.
http://operationsbasednavigation.com/wordpress/wp-content/uploads/2011/07/P773dsurf.jpg

note the area of analysis for the missed on this approach...

I look at it this way...the minimums are the bare minimum to where the procedure would be illegal...
if I designed the procedure that didnt meet the minimums, it would be illegal per the criteria, and not approved...
would you want the procedures designed to not meet the minimums? they are after all MINIMUMS...one can always be more than the minimum...but less?

So basically, you are stating that you just dont care what the basis for that MDA was, you feel that you can drive below that altitude at your leisure.

There are many places in the world where I would NOT suggest trying this.

[alphacentauri]

LSM, just because it is legal does not make it safe. Most regulators in the world at the moment are struggling to have the experience to make informed decisions on such matters. We have been watching the European proposition to convert MDA's to DA's for a while now, and to be honest I don't agree with it.

So I'll leave the decision on this up to you. PANS-OPS says that in the final approach segment I must give you 246ft of obstacle clearance. The MDA is derived by giving you at least 246ft of obstacle clearance from all obstacles. If you convert the MDA to DA with no additional allowances then basically you have (246ft - height loss) clearance from obstacles. For a CAT D aircraft height loss is 161ft (PANS-OPS published height loss) As you can see adding 50ft to a minima to turn it into a DA doesn't seem quite adequate does it??

a) If you want 246ft clearance from obstacles (IAW PANS-OPS) I strongly suggest you don't descend below MDA.

b) If you are happy with down to 85ft of obstacle clearance, then punch on through the MDA at hearts content.

Which one do you think is right?

But do all the procedure designers in the world a favour....if you choose option (b), and the DA was simply converted from an MDA, when you hit something, don't point the finger at us and accuse us of not protecting you.

Sorry if this seems harsh, but there are alot of people running around at the moment claiming to know what they are talking about. When there is smoking hole in the ground, they all dissappear.

[MD83FO]

Our Part A states that 50' must be added to the MDA to account for the height loss in a go around on a CDF NPA. And it is referenced as OPS 1.430 2

Unless of course it is a baro-VNAV where we use the charted DA

[airbus757]

alphacentauri

You could argue the same point with an ILS approach. Work those same numbers with a Cat II.

[alphacentauri]

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?

[airbus757]

Its not the the airplane touching the runway that i worry about. It is when you hit something else that it becomes a problem.

[FlightPathOBN]

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.

[cosmo kramer]

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. :ouch:

[cosmo kramer]

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.

[FlightPathOBN]

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...

[galaxy flyer]

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.

[cosmo kramer]

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.

[airbus757]

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.

[Mad (Flt) Scientist]

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.

[galaxy flyer]

Cosmo,

Didn't say the FAA could, it is true only in the US

[ggofpac]

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 ! :O

[FlightPathOBN]

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]

[atpcliff]

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.

[vilas]

In many countries the DCA has made mandatory to add 50ft.

[flarepilot]

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.

[AerocatS2A]

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.

[BOAC]

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.:eek:

[RetiredF4]

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?

[fantom]

Franzl, they are just kids playing now. No proper knowledge at all.

[flarepilot]

aerocat and boac

I simply meant the following: sometimes the dive and drive technique allows you to see the runway and maneuver around clouds that might otherwise be in the way of a constant descent.

if there is a cloud at the mda in the exact place that the constant descent leads you to, then you don't get in.

if you get to the mda early and DO NOT LEAVE THE MDA until it is safe to do so, you might observe the runway and a way to it that the constant descent would not allow you to see.

I DO NOT, say again, DO NOT advocate leaving the MDA until the runway can be safely made. But the harsh reality of non precision approaches simply means the clouds have to be out of the way...flexibility, crew coordination, precise understanding of the particular approach, airport environment and the like all are part of the equation.

and for the record I do not steepen an approach to a runway if the runway is seen ''too late''.
I also remind you all that circling or non straight in approaches also have an MDA and even with the restrictions airlines now impose of basic vfr to circle, observations at MDA on the early side (or basic vfr equiv for certain airline ops ) aid in the approach.


oh, and just in case...sometimes, in odd situations, a non precision apch may get you in while an ILS leaves you in the cloud for the same runway...

[AerocatS2A]

Understand what you're saying, though the point of a constant descent approach is to hit the MDA on profile (ie 2w/2r on PAPI), so if you can't get in off the CDA because there is cloud on profile at the MDA then you shouldn't be getting in off the dive and drive either if, as you say, you are not leaving the MDA below or above profile.

oh, and just in case...sometimes, in odd situations, a non precision apch may get you in while an ILS leaves you in the cloud for the same runway...

Not in our company it wouldn't, unless the ILS is not aligned with the runway. The final 400 feet we have to be stable including being on runway centerline. Cloud on the ILS at the DA would mean cloud on the final approach of the NPA as well.

[flarepilot]

we have some exceptions to your company's rule.

lining up on final at at least one airport here requires maneuvering at low altitude.

[Capn Bloggs]

so if you can't get in off the CDA because there is cloud on profile at the MDA then you shouldn't be getting in off the dive and drive either if, as you say, you are not leaving the MDA below or above profile.

Not quite. If on a close-to 3° profile with cloud at MDA + 20 on a CDA, you will almost always be forced into a Go Around, whereas you could be level at the MDA for a mile before and get in because you are just under the cloud, especially if the vis is OK. All you do is maintain altitude until flying into the PAPI and then descend.

Given the number of times this scenario is actually encountered, CDAs are better. No worries about bumping into/off/thru limiting steps.

[flarepilot]

thanks capn blogg

originally, these approaches were called, ''cloud breaking approaches''

I also recall at one time, apchs were based on visibility and ceiling...now of course most are just visibility.

[flarepilot]

oh, by the way...some ILS approaches have higher mins than some localizer only for the same runway...interesting huh?

[aterpster]

flarepilot:

oh, by the way...some ILS approaches have higher mins than some localizer only for the same runway...interesting huh?

TERPs 101. The visibility for the ILS must be geometrically valid from DA to the threshold. Not so for NPA minimums.

[Capn Bloggs]

oh, by the way...some ILS approaches have higher mins than some localizer only for the same runway...interesting huh?
I'm interested! Please post one or tell us what approach it is so we can look on Airnav.

[roulishollandais]

Europe once again shows its anarchist face against UNO/ICAO system. They contest the laws, the logic, the reality of the ground's and obstacles' limits. Please don't fly out of Europe and don't transport not European passengers. (But once again what is "Europe" and which "Europe" - ICAO European region, European Union of 28 sovereign Countries, Eurozone, Benelux, Geographic zone from Atlantic to Oural? ?) Watch Europe's crazy history ! Aviation safety and travel freedom needs to have only one system based on international worldwide treaties in ICAO. Millions People died during worldwide Wars to get SUCH FREEDOM in a SAFE world.

Constant descend angle method once again shows its ideologic agressive and limited private conception.

Dive and drive method respects the actual ground's shape irregularities and is building approach procedures at minimum price with minimum descend (and not decision) altitude. Dive and drive concepts are build on experience of pilots, not on insurance rates and off-shor Banksters connected to Kings and Queens European Countries. Dive and drive method respects operational mathematical analysis rules where TWO sorts of parameters - and not only ONE - are used differently : 1. variables who state Limitations ("constraints"), and 2. adjustables variables who increase performance, wealth, optimization. In the approach design the first are mandatory couples distance/altitude (true altitude not baro dependant indicated altitude or angle), the latter are used to verify the path (tables in NPA) but are not mandatory.

I would like to refer too to the existence of the 15% rule of obstacle clearance in NPA procedures design : The captain of the F-GGED crash flew it (220 kts, 3300 FT/mn) but could not see he had to stop at 3660 FT until the FAF ar 7 NM DME to STR VOR, as the AF/ATLAS chart did not show the FAF position where altitude is mandatory. Appearant "Constant" descend angle method just ignores it.... as it decides to ignore MDA is ground- minimal.

[roulishollandais]

@ RetiredF4
I'm shocked too!

[flarepilot]

capn blogg

check out KRNO, reno,nv usa...both ILS 34L and LOC DME 34L

look under cat a and b...loc dme has lower vis req than ILS

[safetypee]

Although not a direct comparison, an old NPA to Zurich 29 had visibility minima where it was impossible to see the runway at 'MDA' when on the approach path.
The then procedure design assumed level flight to MAP, from which if the runway was seen resulted in a 6 deg flight path.
Unfortunately it took a tragic CFIT accident to alert the authorities to this and change the procedure, and ultimately to install an ILS.
IIRC this accident also strengthen the case for EU CDA regulation and procedure review by ICAO; perhaps other authorities have yet to learn, adopt CDA, or implement the MDA concept.

[Tourist]

roulishollandais

"Millions People died during worldwide Wars to get SUCH FREEDOM in a SAFE world."

I was not aware that WW1+2 were about the right to fly NPAs in a certain way.

Thank you for enhancing my education.

[Capn Bloggs]

check out KRNO, reno,nv usa...both ILS 34L and LOC DME 34L

look under cat a and b...loc dme has lower vis req than ILS
Fascinating. Thanks. :ok:

[OK465]

http://155.178.201.160/d-tpp/1309/00346I16R.PDF

http://155.178.201.160/d-tpp/1309/00346L16R.PDF

Lower mins, both ceiling & viz, for all cats, ABCD + additional E on the LOC, both straight-in and circling, versus the ILS.

Why would anyone fly the ILS in preference other than to avoid reading the note about glider activity? Long live the NPA. :)

There is an LPV with even lower mins ceiling wise, lower viz than LOC for CD, higher viz than LOC for AB.

Go figure.

http://155.178.201.160/d-tpp/1309/00346RX16R.PDF

[BOAC]

I assume it is the different slope that raises the minima although that is a mighty jump to 7SM! I guess it must be the 6361' or 6219' that does for the ILS. Why put in a 3.1 ILS??

[OK465]

True the LOC is 3.49 VDA to 55' TCH....but both the ILS & LPV are 3.10 degrees to a 63' TCH??

Identical slope & TCH and the LPV gets you ~1200' lower mins than ILS.

Terps 102? :)

[BOAC]

Ah - didn't look at the LPV plate.....................yes, strange. Interesting too that the ILS does not refer to the MALSR, but since it appears little more than a 'cloudbreak'..........................

[flarepilot]

dear capnblogg

you are welcome...and thanks for the civil conversation...so many say things are not so.

I grew up flying in nutty mountainous / special airports all over the USA...go figure.

Reno, Lake Tahoe , Truckee...all mountainous with unique stuff

unique stuff back east too.

all i'm saying is that whenever anyone says NO...well, you have exceptions somewhere.

and I could tell you stories about ...well, that would just garner someone calling me a liar and i'd rather be a flyer than a liar.

folks, you can also check certain notes about papi not being useable more than six miles out due to terrain...and I mean TERRAIN.

[Desert185]

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).

[AerocatS2A]

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.

[Desert185]

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.

[flarepilot]

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.

[roulishollandais]

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??? .:E Stabilizing the approach in short final is fine on airliners but the intermediate and final approach must manage TRANSIENT regimes.

[Desert185]

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

[Capn Bloggs]

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:

[RetiredF4]

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/thumb/101020-1.jpg/800px-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 (http://www.icao.int/APAC/Meetings/2013_APRAST3/6%20-%20CFIT%203CASA%20AC%20008A%20CDFA%20Final.pdf)

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).

[Capn Bloggs]

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.

[RetiredF4]

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.

[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.

[Capn Bloggs]

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.

[Lord Spandex Masher]

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.

[BOAC]

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

[Desert185]

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.

:yuk: :)

[Capn Bloggs]

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.

[flarepilot]

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.

[AerocatS2A]

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.

https://lh4.googleusercontent.com/-zhJkKnJrapw/Uh6TKZl1IfI/AAAAAAAAAT8/nA-rzYm3neY/w396-h611-no/Screen+Shot+2013-08-29+at+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.

[Capn Bloggs]

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]

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.

[AerocatS2A]

Ah, the bunch that still fly the quadrapuff have something against using the charted profile, I'd assumed you guys in the faster twin-jet had inherited the same reluctance to change.

[BizJetJock]

lowering the nose to commence the descent (bunt)

Hmm, where I grew up a bunt was specifically lowering the nose with sufficient vigour to produce negative g - not sure my pax would appreciate that!!:O

[Capn Bloggs]

I'd assumed you guys in the faster twin-jet had inherited the same reluctance to change.
If it ain't broke, don't f... with it!:)

[AerocatS2A]

This is so confusing....could this not be done from level flight at any altitude?

....say for example, the MDA.
Sure, but get it wrong from the MDA and you have to go around, get it wrong from 30,000+ feet and you've got 29,000+ feet to fix it ;). Not to mention that it goes against the philosophy of a stabilised approach.

[roulishollandais]

You are not allowed to descend more than 15% to have a constant margin to be protected from obsracles
What is wrong with the step by step schematic is that occasionaly (tired pilot, error, etc.) the pilot may think he is allowed to pass D10.0 aswell at 3000' or 2000', D7.0 aswell at 2000' or 1300'. The red line is the real bottom step by step path. BUT it is possible that the pilot descending the CDA does the same fatal mistake... So charts' drawers would not draw square steps but figure the 15% slopes with the distances. So the confusion is no more possible. The confusing grey zone exist already in the official documents about approach path design.
. (I did a mistake calculating the average position where you cross the CDA path at MDA 490' : The distance to AD is 2.0 NM and not 2.8 NM. Please correct.)

http://i1166.photobucket.com/albums/q601/femmes_pilotes/NPAjeppessen15_zpsea6c9005.png

[AerocatS2A]

The presence or otherwise of a depiction of a 15% descent slope to each step makes no difference to my point. If you remember, you said I cannot claim to only use a constant descent method without any dive and drive, I showed exactly how I fly an approach using constant descent and no dive and drive.

[Capn Bloggs]

the pilot may think he is allowed to pass D10.0 aswell at 3000' or 2000', D7.0 aswell at 2000' or 1300'.
That anybody could confuse the grey "no go" zones is a bit of a concern.

Putting the dive and drive on that chart shows how complex D and D really is. That is the beauty of the chart; start at 10DME at 3000ft, dial in/set up a 3° slope and miss every limiting step on the way down. But most importantly of all, you can check your progress down final before you get to any limiting step. In any case, just get on and stay on the Distance/Altitude table and you will 1/miss every limiting step and 2/arrive at the MDA/DDA 2W/2R on the PAPI.

BUT it is possible that the pilot descending the CDA does the same fatal mistake...
No. Follow the Distance/altitude table until on the PAPI and you will not run into anything. Simple.

[roulishollandais]

@ AerocatS2A
When experienced pilots are crashing after many many correct NPA approaches, are these approaches step by step or CDA, we have to ask us which wrong idea came in their mind that last flight. It is a problem of pedagogy, of didactic of failure. "Errare humanum est " is the norm, and someone think that replacing human by robots is the solution. But "Errare humanum est" works for automation, systems or SOP designers too. We just changed the reason of the crash. We have then to try to do a walk of empathy beside the thaughts of the person who failed that day. It is the main work of the agencies enquiring and elaborating recommendations not always connected to the day's accident.
We are searching which stimulus or lack of stimulus suggested the crew that action that day . Descending step by step with an altimeter and a DME seems one of the easiest task wanted from pilots. But we know sometimes they failed to achieve it. It is one reason to imagine the CDA "surfing" on the top edge of the steps. And we see they still decided to descend hundred feet under that line (last one Birmingham,AL). WHY? HOW?
I examined many times the AF chart in the Ste Odile crash before I understood how the FAF missing induced the idea that D7,3660' lost the state of mandatory. It got just numbers to eventually help. But that day was not like another day (you know any flight is different) and they descended the 15% slope toward 1440' and crashed at 2620' as their knowing of the bottom of the aproach was wrong. One of the expert said me he ignored the 15% limitation rule and no more came to the trial.. Today the status of CDA is still increased with RNAV or GPS approaches and the grey zone appeared in the books. The charts tried to figure together the CDA and the step by step informations. But the square grey zone is dangerous letting the possibility of confusing the bottom position.
Surely AerocatS2A your seem to have a strong use of your correct method help adequate training. In our times where beancounters consider training is too expensive many pilots are not so clear as you.Andpilots are not enough taught about the 15% slope, its beginning distance and finishing distance and that is confusing in the mind in the unconscious gey zone of the brain. Then these grey square zones may confuse the tired brain not help.

[roulishollandais]

BUT it is possible that the pilot descending the CDA does the same fatal mistake...

No. Follow the Distance/altitude table until on the PAPI and you will not run into anything. Simple. Yes! SIMPLE! But they did NOT and crashed (unless altimeter mistake and other founding of the Enquiry).
WHY? HOW?

[AerocatS2A]

Yes! SIMPLE! But they did NOT and crashed (unless altimeter mistake and other founding of the Enquiry).
WHY? HOW?
Well for starters the American charts don't appear to have a distance/altitude profile of the type displayed on the Adelaide chart, so unless they made up their own profile they did not have anything to get on and stay on.

I'm not really sure what is confusing about the grey zones, they are areas you are not permitted to fly. As far as being taught about the 15%, I must say I didn't know about it, but I don't need to know about it as my approach descents are all somewhere around 5%. In fact the descent rate required to break 15% would have to be up over 2000 fpm so I don't see that it is relevant.

[Capn Bloggs]

When experienced pilots are crashing after many many correct NPA approaches, are these approaches step by step or CDA,
Let's not get carried away. What pilots have crashed doing a CDA using the chart type/technique that Aeroscat has posted?

Andpilots are not enough taught about the 15% slope, its beginning distance and finishing distance and that is confusing in the mind in the unconscious gey zone of the brain.
Perhaps that is the problem. As far as I am concerned, the 15% slope stuff is totally irrelevant. I have never ever done D and D and I suspect that that is the problem (not your problem but those who use D and D).

A brain-reset is required; remove all concepts of D and D and 15% and start with a clean slate. :ok:

[underfire]

What is the reference for 15% slope for obstacle clearance?

The ROC is based on segments.
Typical ROC values for en route procedure segments, 1000 feet (2000 over designated mountainous terrain);
for initial segments, 1000 feet;
and 500 feet for intermediate segments.

At the FAF, you have a ROC of 500 feet and it tapers to 200 feet minimum.

These ROC's are nothing along the lines of 15%, with FAS ROC being on the order of 1:40 to GPA.

I see little reason to D & D on the YPAD procedure, in fact I would persuade against this, knowing how the database for man-made obstacles is managed worldwide.

[roulishollandais]

What is the reference for 15% slope for obstacle clearance? These rules are from the most respected rules around the world, aswell civilian as military. The mandatory rules are, Country by Country, codified on the base of that document [PDF] ICAO Doc 8168 - Vol 2 - PANS OPS Approach ... - Code7700 code7700.com/.../icao_doc_8168_vol2.p... Aircraft Operations. This edition incorporates all amendments approved by the Council prior to 3 October ...

The French Civilian document is published by SIA (Service de l' Information Aeronautique) depending of DGAC in the document known as PRO-MIN. (The two pages are non updated extracts)

http://i1166.photobucket.com/albums/q601/femmes_pilotes/neutralisationdesobstaclesVOR-DMEtextenew_zpse3d73c0c.jpg

http://i1166.photobucket.com/albums/q601/femmes_pilotes/neutralisationdesobstaclesVOR-DMEshemanew_zpsaa401818.jpg

[roulishollandais]

That is about how the most important danger of the step by step happens in a bad taught or tired brain happens.
Typical virtual exemple : The pilot at D11 to AD of our (for virtual pilots only) Adeleide's VOR 05 map projects himself to D10 which is 3000' protected but according the square grey zone, seems to be protected at 2000' and then decides to start descending to 2000' to descend more continuasly, and crashes on obstacle a 2700' before beeing at D10 to AD.

Any good formation of NPA gives opportuitty to the student to get aware of that (only) NPA risk.

That risk exists too with no grey zone, only the fix points if the pilot is ignorant of the 15% rule in a bad working brain. It does not need much flight time to learn that for ever, but MUST be well taught and is not enough/well taught.

To improve the NPA about that risk, tables of computed couples [Distance,ALTITUDE] have been edited on the approach charts, keeping fix points limitation. The pilots learned too to reckon themselves such couples and correct pitch and power if you are a liitle in advance or late. Tables are never mandatory. Points are (and the hiden unknown, not taught 15% rule) are mandatory.

The risk continues to exist of confusion with the CDA profile when the brain is little working due to fatigue, bad training, etc. And then you have Birmingham and other crashes after descending under the steps /fix or MDA altitude.

If you draw the 15% slope and learn the pilots the 15% rule the risk of confusion not more exists! Magic! :ok:

Didactic problems are the true "human factor".

[underfire]

roulish,

The 15% is on track, ie horizontal obstacle clearance,
not on slope, which is vertical obstacle clearance.

The 15% is not vertical obstacle clearance as referenced in post about the D & D profile.

[roulishollandais]

@underfire
It had a look on the two pages, it is unclear.
Which is the number of the post you refered to ? If it is vertical and horizontal the D number are different, but otherwise it is the same.
Thank you for verifying.

[underfire]

Obstacle assessment areas for procedure design are different than obstacle clearance areas.

http://i41.tinypic.com/110aqmh.jpg

[roulishollandais]

@underfire

I am glad you help to do these rules clear and taught to pilots.

Unless you are at A you may have an obstacle at 15%.

Your picture referes to an isolated obstacle, whose rules are not the same that for a mountain.

I had been in trouble about your vertical and horizontal, but your formulation was not clear. For the moment I stay with my first version.

http://i1166.photobucket.com/albums/q601/femmes_pilotes/MDAunderfireA15110aqmh_zps1767f2f5.jpg

[underfire]

This is to verify/validate the location and altitude of the fix.

Note the straight steps at the fix locations, not a 15% taper:

http://i41.tinypic.com/2crveao.jpg

OCS surface straight lines, hence the confusion:

http://i40.tinypic.com/2ntfceb.jpg

[7478ti]

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).



When using minima based on this appendix in conjunction with a DA(H), flightcrew procedures for timely initiation of a go-around and anticipated altitude loss below the DA(H) during the momentary transition to a go-around are assumed to be the same as those specified for ILS, MLS, or GLS. The procedures used may be as specified by the operator or by the aircraft manufacturer, as applicable.



When using minima based on this appendix in conjunction with an MDA(H), it is recognized that the missed approach path following a stabilised approach may momentarily descend below MDA(H) while initiating the missed approach. 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.

[roulishollandais]

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.

[RetiredF4]

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/media/Notice/N%208900.183.pdf

[underfire]

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.

[underfire]

going below the DA during a go around from minimum

Really? (just think about that statement) :ugh:

[beech35]

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.

[underfire]

John,

Like I said..think about it.

going below the DA during a go around from minimum

[Pugilistic Animus]

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

[7478ti]

@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.

[RetiredF4]

@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.

[BOAC]

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.

[underfire]

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.

[EGPFlyer]

I'm sure the use of the word 'minimums' was because that's what the aircraft says when you reach DA.

[LeadSled]

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.

[Capn Bloggs]

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?

[LeadSled]

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!!

[Capn Bloggs]

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.

[LeadSled]

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.

[LeadSled]

‘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.

[roulishollandais]

[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.