MDA for CONSTANT DESCENT NPA
 

I know this has been industry-wide practice now for a long time, but can anyone quote me either ICAO or Jeppesen reference to the requirement to add 50 feet to the published MDA for a NPA when flying the now-standard constant descent angle approach technique, to allow for the height loss on a go-around on say a category C airplane?.Also any decent paper on this subject written by ICAO or other professional source explaining the logic behind this practice (for training purposes).Many thanks Pete.

Now standard, with whom?
At our mob, we still dive and drive....works good, lasts a long time (properly applied, of course).:rolleyes:

Standard in Europe 411.....

Pete, it's in our ops manual and charts (we have company charts from LH Systems)

PT6

My understanding is that one may not descend below the MDA , without visual reference ; therefore the habit of adding 50 feet for a Cat C aircraft will hopefully ensure that in the event of a Go Around , initiated at the 50 foot point , the a/c will not go below MDA ( and you will not fail your check ).
With a DH , the missed approach must be INITIATED at or before the DH and a subsequent sag below DH is acceptable.

pp - we've had this discussion recently here! Have a look here. Note the link to the Jepp info. There is more bedtime reading here As '737jock' says, there is now the option in EU-OPS anyway of establishing a DA for an NPA which will not cause the a/c to descend below a safe obstacle clearance during a g/a. It will be company specific in the OM and some may take a while to change. Note the 'divers and drivers' are required to increase min RVR for their approaches.

As 'backofthedrag' says the whole definition of 'MDA' was that you could not go below it in a g/a and hence the (various) additions for different a/c in different OMs (50' in my lifetime). MDA was an abbreviation for Minimum DESCENT altitude ( not DECISION). Obviously a change to a 'real' DA will need a review of the figures used. It will certainly make like easier at the sharp end.

I believe implementation of the new system has to be sometime in 2011.

Like many things 'European' it is riddled with scope for confusion!

Surely the "add-on" depends on the a/c type? On the B737-200/300 it was 35 ft (defined I believe somewhere in the AFM). For CAT A types we used 10 ft and then also added the max pressure error correction of 50ft, the latter also specified in the AFM.

My company does not add this 50' to an MDA. In some cases, and these are the cases where the weather is on the limit, during this 50' you will see the rwy and a G/A is not necessary. If not, there is still enough margin to safely execute the G/A. I had already tons of NPA's where this was the case.

So you're saying that you initiate a G/A AT MDA and knowingly go below MDA because there is "enough saftey margin"?

The DDA is required for CANPA.

- see what I mean about confusion. As written there that company is operating illegally. A minimum is a minimum!

I realise this will cause an uproar, but realistically 50 feet is going to make stuff-all difference in terms of flight safety in a go-around from an MDA on a non-precision approach. The lowest MDA I know of is probably around 350 feet and if for decades the normal published MDA has been used from where a go-around is commenced (whether dive and drive or a constant angle descent) I doubt if there are hundreds of aircraft spread over the countryside simply because they went below a MDA by 50 feet on an instrument go-around. Isn't it all really a storm in a tea cup? Having said that I realise there is a question of legality.

The MDA has been designed decennia ago when aircraft were still driven by props. In these times, you descended to MDA and kept that altitude until visual or at the MAP nowadays, nearly all companies do a CDA. based on the DME/altitude readings on the profile. it is therefore considered that an MDA is in fact a DA.
As previously mentioned, the DA and MDA will be the same in the new procedures. No need to add this 50'.
Operating illegally?! Don't make me laugh! Our OM is approved by a major EASA state and my company is well known for its good standards.

Dive and drive is stone-age. Is "your mob" the "fly it like a 200 mob?"

LNAV/VNAV or CANPA is much more stable/safer way to go. Drive and drive "not applied properly" = GPWS warning now and then.

Hi despegue,

What aircraft are you operating?

If you are using dive and drive to MDA then you must have commenced the level off before so that you didn't sink below MDA. (at MDA + 50 say?)

We can't satisfy the stable approach criteria with the level segment below 500 feet AGL so we must use a continuous descent profile.

Even LNAV/VNAV is old now, the newfangled thing for boeings is IAN. Everything is flown with identical procedures and indications, be it ILS, GLS, or any kind of NPA.

That said we do not add 50ft to the MDA, however we have to initiate the go around latest 50 feet above an MDA, if a DA is used instead no added safety margin is needed. Sadly the 50' above an MDA thing is put into a small note that is very easy to miss, simply bad presentation in our present manuals.

Thanks
 

PT6 and BOAC, thanks kindly for that info.I know most operators have the procedure in their ops manuals also AFM has the actual 'aircraft allowance' but where else is this CANPA information published.Sorry im currently working somewhere I cant access a Jeppesen manual, and my current employer has never heard of this stuff (dont laugh), perhaps 411A is the DFO here, and has banned any discussion of the dreaded "constant descent NPA", cheers Pete.

Hi, guys I understand diference exist on a DA and MDA but I never see in a paper those 50 feet that you are talking about, and the initial post is asking about a reference to find these matter.
toby

Yup, and it suits this stone age guy just fine, thank you.:rolleyes:

Illegally...nonsense. They don't add 50 feet, and apparently don't descend below MDA without visual reference.
We do exactly the same at our mob.
50 feet is for the uninformed.
Or those that can't fly level at MDA.

- read his post again? - and in others? Yes - he could well descend below M Descent A without visual reference. I cannot see how you arrive at your conclusion!

Not to mention flying level at low altitude... breaking out and diving for the runway = unstable approach...

When we have the tools to do it better why do it the old way?

Not an issue for my company as if the airport does not have an ILS we have a company RNP approach with CAT 1 like minimums...

PT6A

BOAC has it right in post #7, the links are all good information and 'dive and drive' (as it's commonly known) will be a thing of the past in a few years (or maybe decade where 411A works) except for circling approaches.

FAA currently requires 50' to be added to any CANPA MDA UNLESS the OPERATOR has been granted permission to use the published MDA without adding 50'.

For dive and drive everyone uses the published MDA - no 50' additive.

For CANPA everyone adds 50' to the published MDA unless special permission has been received from FAA to delete the 50'. (It's said FAA was initially concerned that the newfangled CANPA would be so unfamiliar to crew they might become confused and not respect the "absolute floor" of the MDA as they were long accustomed to doing for dive and drive approaches:))

BUT, if an individual operator has trained it's pilots to FAA satisfaction, then that carrier MAY receive permission from the FAA to delete the 50' additive. Then you get to use the published MDA the same as someone who does the now frowned upon (except for circle approaches) dive and drive. Only your flight department will know if your operation has been granted permission by the FAA to delete the 50'.

For pilots flying under FAA rules the answer is in the column you select on the Jepp approach chart . Some airports have both a LNAV column with MDA and a LNAV/VNAV column with a DA. If you are using the column with MDA minimums AND you are using CANPA, and you don't have permission from the FAA to delete the 50'; - you WILL add 50' to the published MDA.

If you're using the column with DA minimums you fly to the DA.

That's for FAA. The links in post #7 explain what the rest of the world does.

We don't 'dive' toward any runway, we apply normal descent techniques to the runway.
In addition, we often circle at 600 feet (the lowest we can go with our heavy jet) and you simply cannot apply CANPA for these ops.
In fact, this was mentioned earlier, here...
It would therefore appear that the fine art of circling and/or actually finding the runway during non-precision approaches is lost on the younger crowd...and many of the older crowd as well, who have apparently lost their skill somewhere along the line.
All this is in line with the general lack of hand flying/handling skills that we often see today.

Not exactly...
 

The CDA (Constant Descent Approach) is the result of technology...the ability to select a prescribed descent angle. It is a huge advantage for pilots when executing non-precision approaches....especially in large aircraft.

Some authorities allow the CDA to the MDA, without allowing for inertia; some do not. FAA is a case of an authority who does not. My old company required adding 50 feet to the MDA to allow for a go-around without busting the MDA. Other agencies, other airlines may have different SOPs.

411A....you can hand-fly this type of approach, or you can couple it. My old company's SOP required the autopilot....but that was our SOP. But, I ask you, what's the difference of flying a rate-of-descent or descent angle?

Fly safe,

PantLoad

Changes in ground speed are automatically accounted for.

MDA for CONSTANT DESCENT NPA
 

Hi folks,

when reaching DA we make a decision. After a decision for a G/A it is physicaly imposible to go without descending below DA. That is allowed! The allowed hight loss depends on the A/C category.

To descent below a MDA is not yet allowed. That´s what I know. So I add 50 ft as well.

But: meanwhile you can find some Jepessen NPA charts with a DA published not a MDA!!!

I can´t find any rule within the EU OPS that allows a descent below such a published DA for a NPA.

Doe´s anybody know where we can find such a rule?

We do both at our mob, as the situation dictates.
The idea is to have the longest possible time to find the runway, and thereafter land, using normal rates of descent whilst doing so.
I can appreciate why some airlines use CDA, especially larger ones with possibly quite junior First Offciers, however...we have experienced F/O's with good experience on type (L1011) and therefore can indeed fly level at the MDA and/or circle at the MDA, and actually land at destination, rather than diverting.
All it takes is practise.
I suspect the real reason why airlines today do not use dive/drive (and/or circling) is it takes training time and this equates to proper funding...so the easy way out is CDA
Therefore, all the diatribe about CDA being somehow 'safer' is nonsense.
It is only safer for those that do not know how to do otherwise...properly.

In my airline the SOP for CDA is to fly it on automatics, set the MCP ALT to the MDA rounded up to the nearest hundred feet, not to get extra margin but since you only can set the MCP ALT in hundreds. Hence the MDA is not busted and the desicion is made already on the ALT ACQ (737NG) mode change. If not visual then, wait for the ALT HLD and then execute the go-around. Obviously this has the effect that some approaches could have lead to successful landings instead of G/As, when the weather is right down to the minima. Not saying this is the way to do it, just saying they way it is done...

Hi 411A

Would you consider it "safer" to fly an ILS by ignoring the glide path and diving to the "LOC only MDA", fly level to your MAP and then Land?

The dear old TriStar is still my favourite of all I've flown. CAT IIIB 75m No DH in the 1970s - PFM.

But if our modern NAV FMS is able to generate a pseudo "glide path" for our NPA (VNAV, FINAL APP or whatever it's called) as vertical guidance then we can use the published DA on the procedure. If we can't generate vertical guidance (LNAV, NAV only) then we use MDA limits. (+ 50 for us)

If said glidepath was OTS, dive/drive would be my option.
As it is with many older pilots...Lockheed manufactured a fine airplane that was far ahead of anyone else.
A true gentlemens airplane.
Indeed....PFM.

TCASfail - I went to a lot of trouble to provide you with that information. Please read it! The 'rules' are there for you to see.:mad:

Horses and water?

PS It would be nice if all this obfuscation about 'dive and drive' was left for a different thread since it has nothing to do with the topic!

Well...
 

I've done both the 'dive 'n drive' and the CDA.....most of my flying career was dive 'n drive. Both work fine. Of course, dive 'n drive was the only option on my own airplane....back when I owned one.

But, the past few years of my flying I did CDA. I prefer it, without question, to the dive 'n drive procedure.

Just my opinion....

But, the original topic...we did add 50 feet to the MDA and made it sort of a DH...i.e. we flew it like a precision approach. Works great.

rudderrudderrat....yes, you are quite correct. Thanks for adding that.
This is the beauty of the technology.

Personally, I loved hand-flying the approaches. (Not SOP.....but, I did it in VMC.) With the precision the Bus allows, you can really fly a nice approach using Selected Guidance and 'The Bird'. 411A....brings tears to the eyes of us old guys.

Fly safe,

PantLoad

I think 411A is being slightly disingenuous to the younger crowd...unless he has already pointed out that thanks to the marvelous feature incorporated in the 1011 known as DLC (Direct Lift Control), he can make the vertical navigation changes with little change in pitch attitude once landing flaps are set...he doesn't really "dive", he "sedately sinks" and then drives. It is the Cadillac, and always will be.

The fifty foot addition likely has more to do with the approach design criteria. In many cases, the authorities may not have the data to substantiate the missed approach obstacle clearance requirements if the missed approach climb begins at an altitude below the MDA. It is not that it can't be done; just that they have not done it. I note that my current employer adds fifty feet to any non-ILS approach flown with either constant rate or constant angle procedures, unless it has a published VNAV DA. I imagine that some authorities may have different interpretations.

When I look at the confusion generated by the introduction of constant angle, VNAV procedures, I often wonder if more error potential has been introduced than was removed. Nonetheless, the dive and drive technique has a poor history worldwide with respect to CFIT. I also imagine that a VNAV coupled constant angle approach will lead to far fewer misses over time, simply because the captain will be satisfied that the airplane is in a position to land more often than with earlier techniques.

In any event, as I often remarked to trainee pilots years ago, the term "non-precision" in non-precision approach refers to the accuracy of the signal in space...not to your flying technique...whichever one you choose, in this case.

Just had a peek at my trusty Boeing 737-300 FCTM and at page 5.33 is says "set the MDA (H) using the baro minimums selector...if required to use MDA (H) for the approach minimum altitude, the barometric minimums selector should be set at MDA + 50 feet to ensure that if a missed approach is initiated, descent below MDA(H) does not occur during the missed approach.

So for Pistol Pete - I guess if your ops people say they have never heard of this 50 feet addition it maybe they either haven't read the advice in their Boeing FCTM or they ignore it. Could be their local culture of course. Of course they may be operating another type where the automatics are so advanced, the 50 feet additive is not a factor?

No Published DA requires the height loss derived decision altitude which adds 50' to the MDA. If it is published LNAV/VNAV, it has a DA so no DDA required.

Coincidentally dealing with these issues right now with my Air Taxi company, here in the US so it's FAA rules. APV approval not a problem, LNAV/VNAV should not be an issue for us either, but the DDA would be new to our type of operations so I'll let you know how it goes if anyone is interested.

The pilots most likely to bend metal (or worse) today are guys like yourself who claim all their "Chuck Yeager-lke" flying skills are better than technology and avionics available. Like Ice-man said, guys like you are "dangerous". I'm sure the Korean Air 747 captain who hit Nimitz Hill in Guam back in late 90's on non-precision approach doing dive and drive was very comfortable in his hand flying/handling skills and was a big fan of doing the dive and drive if "handled properly'. Dive and drive worked out great for them until they hit Nimitiz Hill and killed everyone when it was not "handled properly."

There are plenty of other examples in aviation history of dive and drive NP approaches resulting in fatal accidents. A constant descent approach, either VNAV or other derived constant angle approach is so much more stable and yes SAFER. I can't find anywhere where such an approach in itself has resulted in an accident. I can find plenty where your favored dive and drive has resulted in accidents.

I am sure your are a great stick, but shouldn't procedures be in place for us average Joe's?

Give it up man. Get an Iphone too :)

Why....
 

Why we make personal attacks against people here....our fellow airmen...is beyond me.


PantLoad

As a long time contributor to PPRuNe, in my view it is from those that simply do not have the skills necessary to complete the task, therefore attack those that do.:}

Early in the year but that has to go down as a front runner for funniest post of 2010.

CDA is better than dive and drive in every regard. If anybody has info regarding a crash from a CDA approach please post now.

411A, have you ever done a CDA approach? L1011 may have been the best newfangled flying machine ever built but the relentless march of technology cannot be slowed. Enjoy your iphone.

As far as I know, there is no ICAO or Jepp reference-- it is up to what your company works out with your regulator.

At my present employer we add a 50' buffer to the MDA for protection during the go around maneuver (since the aircraft will continue descending a few feet from momentum).

However, my previous employer did not add the buffer. When I asked about it, they replied that they had discussed the issue with the regulator and it was felt that it was not necessary-- given that the location that the aircraft would reach the MDA was in the location which it would normally have continued the descent (close to the runway, with sufficient terrain clearance). I was satisfied with that explanation.