Simple answer to CDFA/MDA question please...

[WX Man]

I have trawled through the other thread about Jeppesen charts and CDFA/MDAs.
http://www.pprune.org/tech-log/441886-jeppesen-approach-charts-non-precision-da-4.html

And haven't really been able to deduce a simple answer to my query...

If a Jepp chart marks the minima for a non precision approach as "CDFA", do I still need to add my company's increment to it?

At the moment, we are told that we don't need to add the increment to minima that are marked down as "CDFA", but we do if it's marked down as "MDA(H)".

I don't believe that this is right, because in my previous company we were told that we had to add the increment to all non precision minima- whether it was marked down as CDFA or not.

I dunno... maybe the rules have changed. I've tried interpreting EU OPSspeak, without too much success. So a clear answer would be nice.

[BOAC]

Do you have a company Ops Manual? If so, what does it say? If nothing, do you have anyone in management or training to ask?

[bucks_raj]

AAI publishes OCA - Obstacle Clearance Altitude
Jeppesen Publishes MDA - Minimum Descent Altitude (OCA or More)
When the approach is flown as a CDFA the pilots needs to add an increment of "X" (To be appropriately computed by the company based upon the type of aircraft) to the MDA and create a new number

DDA - Derived Descision Alt -

During a go around the aircraft cannot go below MDA but can go below DDA

When ever on the chart you see MDA you need to add the increment factor to it but if the number published is DDA then you do not have to.

[Kak Klaxon]

Bucks please can you give me the Jepp reference for that or does your company have tailored charts that show DDA?

[bucks_raj]

My reply was IND/ME specific...

http://ww1.jeppesen.com/documents/aviation/notices-alerts/hubwatch/BriefingBullentins/abb_jep_08_D.pdf

http://www.theairlinepilots.com/forumarchive/quickref/euopsjeppesen.pdf

Two links which i could quickly lay my hands on.

Look for CDFA. In compliance with EUOPS even the NPA have DA published

The way to calculate DA wuld be OCA->MDA->DA

Again in an ILS the aircraft can go below the DA but the GA should have been initiated at or by DA but in an NPA the aircraft under no condition should go down below MDA . So incase the number published is MDA in that case you will have to add an Incremental to it to make it DDA or incase the NPA publishes DA the GA should be commenced at or before the DA.

The All Weather Operations circular in IND/ME necessitates the increment to be a minimum of 50ft but again it is opeartor/aircraft specific

In IND/ME jepp publishes MDA hence I am required to add the increment to the MDA Also the authority does not permit any NPA approach to be flown unless flown as CDFA hence any and all the minimums used by me for NPA are always MDA( From the chart ) + the increament = DDA.


Hope it helps

[Kak Klaxon]

Thanks Bucks, we are in agreement but some large UK based airlines don't add anything to CDFA minima and this is approved by the CAA ops inspectors via the operations manual. There must be some Eu Ops stuff allowing this but I have not been able to find a reference. I am sure someone will post it for us soon.

[WX Man]

That's interesting.

In my last company, we added 50ft to the minimums for a NPA, even if they were marked as "CDFA".

This was because, when we compared the same plate before the change (when the minima were marked as "MDA") and after it changed (marked as "CDFA") revealed that there was no difference in the number.

[buzzc152]

Coming back to this thread,

I've trawled through a bunch of docs and as far as I understand it approaches with vertical guidance (APV) - or more correctly called now I believe '3D approaches' (Lnav/Vnav, baro Vnav, Sbas etc) - are down to a DA.
Everything else ie nominal vertical profile or '2d approaches' (ndb, vor, loc, lnav etc) is down to an mda.

That being said, most Jepp NPA now publish a 'da/mda' regardless of the type. For instance if if look at any loc or ndb plate it gives a single figure which is called an da/mda.

Which is it then ? A da or mda ? We still add 50ft anyway but it would be nice to get a definite answer.

[buzzc152]

Can anyone give me an answer on the old da or mda question with regard to non precision app

I've trawled through a bunch of docs and as far as I understand it approaches with vertical guidance (APV) - or more correctly called now I believe '3D approaches' (Lnav/Vnav, baro Vnav, Sbas etc) - are down to a DA.
Everything else ie nominal vertical profile or '2d approaches' (ndb, vor, loc, lnav etc) is down to an mda.

However, most Jepp NPA publish a 'da/mda' regardless of the type of approach. For instance if if look at any loc or ndb plate it gives a single figure which is called an da/mda.

Which is it then ? A da or mda ? We still add 50ft anyway but it would be nice to get a definite answer.

[172_driver]

A few years ago anyone with an IR ticket knew the difference between DA and MDA.

Since then regulators, chart providers, OPS manuals have muddied the waters to incomprehensible levels. On the plates I can no longer tell what's hard altitudes and what's advisory 3 deg. altitudes anymore.

Bring back the old step-down profiles. The Boeing can still fly a nice continuous descent approach and I will know what's terrain safe and what's not.

[Skyjob]

Jeppesen publish a minima, your operation interpret any minima for non-precision approaches as MDA, precision approaches as DA. A chart with ILS and LOC require different minima types but the procedure is charted the same on the same chart.

The "new" approach types you refer to require "new" charts which then take into account the type of approach. They are labelled as such and should not be flown unless charted. Remember your operator could instruct you to fly using LNAV a NPA thus thereby enhancing the accuracy of the approach, but the approach type remains in such case the NPA.

Your Jeppesen charts can have LNAV/VNAV minima published which can be used as a DA subject to operator approval of these procedures to be flown.

Remember any NON-precision approach has an MDA which must never be flown through after initiation of a missed approach, whereas every precision approach (LNAV/VNAV but not LNAV) is associated with a DA at which you can go around and consequently can go below in that process.

In the absence of such "new" procedures, flying e.g. an NDB or VOR to MDA could be flown by the operator using an equivalent DA by using company standard procedures for adding a margin on top of the MDA to create a DA from which an MDA will not be breached, hence your company's adherence to +50ft for your aircraft type in your type of operation; other carriers have different additions to MDA.

[tom775257]

As far as I know, on a non-precision approach, if the procedure uses constant descent final approach (CDFA) and you have the ability to fly it as such rather than a dive and drive, and you have the correct plates/aviation authority approval, you can use the minima as a DA and thus dip slightly below during a G/A. Reason being you should be on a reasonably correct trajectory to land at that point anyway. In the UK the CAA need to approve the removal of the 50' addition to the minima on a non-precision approach - essentially you need to prove your pilots/aircraft can fly a CDFA with sufficient accuracy. At the airline I work for, we use the MDA/DA on a non-precision with CDFA without adding 50' after CAA approval.

This is from memory, might be utter rubbish.

[tom775257]

Skyjob<<Remember any NON-precision approach has an MDA which must never be flown through after initiation of a missed approach>>

Whilst I agree it used to be that way obviously, certainly under EASA that rule isn't there any more subject to some provisos. Whether it is sensible or not, well that is a different question.