MDA for CONSTANT DESCENT NPA

[411A]

Enjoy your iphone.

My First Officer has one, as does the Flight Engineer.
They stare at them endlessly, with seemingly poor results.
When push came to shove, up in Russia, they couldn't even call out, nil signal....however, my trusty Nokia worked just fine...with AT&T worldwide roaming.

So, a pox on the iphone.

[extreme P]

Question remains, have you ever done a CDA approach?

[411A]

Question remains, have you ever done a CDA approach?

Yes, at one airline.
Didn't think much of 'em, either.
Dive/drive works far better.
Of course, if you're not skilled, better stick with CDA.

[extreme P]

Dive/drive works far better.

Why is that?

[BOAC]

Dragging this lurching vessel back to a CDA - do we have a definitive, logical explanation from 'them's what regulates' as to whether or not the 'old' MDA is to be re-calculated (raised?) to derive a DA and if so by whom? Is it now accepted that it was an unnecessary restriction to forbid descent below such? Do the readers here consider the matter has been adequately addressed in terms of ensuring that the change is clearly presented and everyone understands? Any ATC procedure folk to comment?

I hesitate to mention 'D&D' but obviously there is no need for any recalculation of MDA there, only the mandated increase under EU-OPS in minimum RVR for such. This leads to further confusion - can a D&D now use the new DA? Will this DA be 'safe' for terrain clearance when, unless there are further restrictions, strictly speaking there would be nothing stopping a death-defying D&D 'dive' from FAF straight down to the 'new' DA several miles out? Will we have to retain 2 sets of figures on Jepps etc?

[rudderrudderrat]

Hi BOAC,

can a D&D now use the new DA

- I don't think so.

I've only seen DA published on NPA charts with published Lateral & Vertical guidance. If there is no Vertical guidance then a MDA is published.

The only reason we are allowed to sink below the DA during the GA, is because we'll be on profile. The D&D aircraft will be further away from the runway when it reaches it's MDA and will be closer to the obstacles which are considered.

[411A]

Why is that?

If you are truly interested (rather than being argumentative) my reasons are aptly described in post number 28.
All that is necessary is to actually read and understand.

With regards to dive/drive, Harry Truman said it best...'can't stand the heat, stay out of the kitchen.'
The 'new' way seems to be CDA, however....being quite a lot older, and have successfully used dive/drive over many years, we stick with what we do best, the old fashioned way.
And, what's more, the concerned regulatory authority has no objections whatsoever.

[Spooky 2]

This is pretty easy to understand if you leave the flamming and insults out of it.

In the US, the FAA will allow you to treat the MDA as a DA if your training provides for VNAV approaches in lieu of the the dive and drive method of descent. Some here want argue that the D&D is better, or in some cases they just feel more comfortable with it. So be it. That not witstanding there volumes of data that show the VNAV or IAN approach is superior in every way to the D&D method. You can argue along with all the insults, but the data will still prove your wrong on this topic.

If on the other hand your not approved for VNAV along with using the MDA as a DA, then you will continue to use the MDA as your final descent altitude. I believe that the OpsSpec for this is B036, but don't bet the farm on that.

As others have noted the additional 50' was imposed on the operator so that they would not descnd below the MDA on a go around. In the case of Boeing the 50' is applied to Boeing aircraft from the 737 to the 787. No differences within the fleets.

[rudderrudderrat]

Hi 411A

being quite a lot older, and have successfully used dive/drive over many years

I bet you're not older than me! I'm now using CDA NPA with FMS (FMGS) generated vertical profile - something my dear old TriStar couldn't do. If your FMS could provide an accurate VNAV profile - I bet you'd use it too. It's PFM (well almost).

However, if you can't do VNAV approaches I can see the advantage of the extra time you'd have at MDA up to your MAP, and the brilliantly clever DLC giving instantaneous change in VS.

Horses for Courses.

Regards
Last Memory items for 2nd Eng Failure.

[411A]

However, if you can't do VNAV approaches I can see the advantage of the extra time you'd have at MDA up to your MAP, and the brilliantly clever DLC giving instantaneous change in VS.

Exactly....you've got the message.

[beerdrinker]

I fear I have to reply (not as a young first officer but a 20K+ hours ex Check Airman on two types of wide bodies) to 411A's dated opinions on Dive & Drive.

It was considered many moons ago to be a potentially dangerous manoeuvre by Aviation Authorities around the world for a number of reasons including the fact that it encouraged dirty dives towards the threshold and deep landings.

Most MAP's are very close to the runway threshold. If you do a Dive and Drive approach you dive to around 500ft agl (typical NPA MDA) and then drive towards the MAP peering out of the window for a sight of the runway. You see it and and dive towards the runway, with a potentially dangerous rate of descent, risk landing deep and running out of runway.

Modern thinking is for a stabilised approach from 1000 ft agl. There is no way an approach is stabilised when one makes a power on. approach flap, level flight at 500 ft agl, sees the runway, then makes a sudden power rduction to get the dive started, select landing flap, and dive for the runway and then have to apply power to stabilise the approach, before actually going into the flare, power reduction and land.

The CDA, aided by timing and /or distances brings one down to MDA from where, if the runway is in sight, the constant (safe) rate of descent can be continued down to a landing in correct area of the runway.

The CDA either in modern aircraft with VNAV help automaticaly or manually, or older aircraft with basic instruments is the safer way to fly NPAs and that has also been recgnised by the FAA.

BD

[Spooky 2]

Well said Beerdrinker. The D&D cannot hold a candle safety wise to a well executed VNAV type approach whether it be coupled or handflown. The record books are full of accident reports utilizing the D&D methods. I realize for various reasons some would choose the D&D over the more stabilized VNAV concept, be it their particular equipment or other issues but one cannot argue with the safety, economy and overall sucess of the VNAV/IAN approach concept.

[rudderrudderrat]

Hi 411A I've left a PM.

Most MAP's are very close to the runway threshold. If you do a Dive and Drive approach you dive to around 500ft agl (typical NPA MDA) and then drive towards the MAP peering out of the window for a sight of the runway. You see it and and dive towards the runway, with a potentially dangerous rate of descent, risk landing deep and running out of runway.

What's the difference if your stop watch timed CDA NPA leaves you slightly higher than the ideal profile so you only see the runway at your DA (MDA + 50?) just before your MAP?

I would suggest that both crews should GA from that position.

[FE Hoppy]

I think you will find that your charts have the extra height built in to the MDA. You just don't realise what you are doing.

you cannot fly a "precision like" CDA to the old MDA and then go around. You must descend below MDA in that case and this is not allowed.

I would suggest comparing your company minimum on one of these approaches with a standard MDA from a company who dive and drive.

[Spooky 2]

FE Hoppy, I can only speak to the Jepp plates, but if there is a DA posted in lieu of an MDA, that's what the operator is approved for REGARDLESS of their OpsSpecs. If on the otherhand there is an MDA and the operator has the "OpsSpecs approvals" that opertor can use the MDA as a DA and use that value. IF, the opertor does not have the approval, they must add the 50' to the MDA and use that new value. That 50' is not shown anywhere in the Minimums block and it's simply an operators specific limitation.

That may be what you just wrote, but for some reason I did not understand it that way.

[411A]

If you do a Dive and Drive approach you dive to around 500ft agl (typical NPA MDA) and then drive towards the MAP peering out of the window for a sight of the runway. You see it and and dive towards the runway, with a potentially dangerous rate of descent, risk landing deep and running out of runway.

In actual fact, this is totally not in agreement with our ops.
We start an 800 ft/min descent at the final fix (and if landing straight in, select landing flaps, which includes DLC, as noted before by another poster), level off at MDA and look for the runway.
If it is not in sight until close in, we don't 'dive' for said runway, we don't land long, we go missed approach.
However, if the runway is in sight at a reasonable distance, a normal descent is commenced toward the runway.
Quite simple actually, IF you know what you are doing.

Clearly many here don't, therefore I would suggest that they stick to CDA.

In the L1011 however, it works like a charm.
No problems whatsoever.

[Meikleour]

Beerdrinker:
As a contemporary of you I applaud your efforts here but 411A has never knowingly admitted to changing his mind. in over 7,000 posts!! That says it all really.

[galaxy flyer]

I cannot resist posting, sorry. Why when given the choice between having an ILS-like presentation thru, LNAV/VNAV (or LPV) approach with a charted DA, would any professional pilot choose a "dive and drive" NPA? The minimums are the same, if you follow the "dive and drive" technique to a visual descent point, the distance from runway when the decision has to be made, is the same. There is no reason not to use the simpler and safer approach method, other than an attachment to old ways.

Flying the F-100C down final at 185 KIAS, with a 3" MM-3 AI and raw data, was challenging and made for a fast crosscheck, is that a valuable skill anymore? NO. It is the 21st Century, use the stuff that is proven safer and more reliable.

GF

[777AV8R]

'Beer' and 'Galaxy' have come as close as anyone to explaining this thread. I too have 20K+ and am an active checkpilot on the B777. I too have flown the L1011. Time to move on.

My memory isn't 'long enough' to remember when the concept of CDAs came into being, but this isn't something new. In view of a number of disasters and incidents having to do with loss of situational awareness to name only one; industry, technical safety groups, regulators, manufacturers, and training organizations put forth the idea of CDAs. Eventually, Jepp notified users through a Briefing Bulletin, that it would begin publishing charts to include recommended 'Distance/Altitude' on its charts to aid in establishing CDA approaches. These strips would only be published on approaches that could provide adequate obstruction clearance to approximate a 3 degree slope. Furthermore; the 'strips' would closely approximate a glidepath of 3 degrees to the MDA. This was pre-VNAV days. I flew these approaches into Geneva and practiced them regularly and they worked well. (both L1011 and 777 in '97-'98)
I was fortunate to be invited to a Boeing checkpilot meeting in the spring of 2001. We talked of stabilized approaches and then we talked of VNAV approaches in specific. We were informed that Jepp would begin to 'code' all approaches so that VNAV could be used on all non-precision/GPS approaches and that the philosophy was to allow the flight to descend continuously in a stabilized energy condition to the MDA which would closely approximate the Visual Descent Point. All of the VNAV approaches were designed to use full automation but the flight crew could still use the FD in VNAV mode, all the way down to MDA. In fact, it is a fun maneuver to manually fly the VNAV 'all the way down' and watch the PAPI...always 2 white-2 red. Note that I talked of stabilized energy conditions earlier. On a stabilized CDA approach, we have near constant energy conditions all the way to MDA and if conditions permit, through to the beginning of flare, where energy changes.
If conditions at MDA do not permit a landing, only one change of state is required from the CDA and that is of nicely entering TOGA and the energy state changes to go-around.
When practicing a CDA either in VNAV or using FPA or VS using the briefing strip dialogue, the result is usually the same: The aircraft is always stabilized throughout the approach and the runway (conditions permitting) will appear exactly where it should be: at the MDA and the PAPI will be in the correct slope.
Derived Decision Altitudes (DDAs) came about as a result of these approaches NOT being thought of as precision approaches and that the maneuvers weren't as accurate as an ILS approach, thus a 50 ft drop-out cushion was allowed for pilot or autopilot 'dropout'. After years of operational proof, it has been found that the VNAV approaches are almost as good as their ILS companions and some regulators will allow for a CDA DH because the accuracy has been so good. In fact, there has been some talk that we will see VNAV approaches down to 200 ft. minimums.
As far as providing documentation on the 50 ft. DDA, the information has crept through training manuals and company operation manuals and has always been a briefing item during sim training and checks. Boeing's philosophy was that they have wanted to see a VNAV approach that was good to a 200 (h) minimum.

The fact is that CDA approaches, without a doubt is the safest method of performing a non-precision approach to minimums for reasons that I previously stated. Times have changed and most good pilots have changed with it.

[BOAC]

777 - thanks for the useful insight. Do I deduce from your post that the 'new' CDA DA is primarily intended for VNAV ops? Does that imply that the V/S type of CDA may well retain the buffer?