Yeager wrote:
It´s subject to the operator using the data provided by other operators having performed the analyses (successfully) of the approach for the 2D approach to DA, as referenced in the GM.
I don’t understand how that can be the case – from a regulatory standpoint. But maybe that doesn’t matter. As you say, in the end it is a question of what you are comfortable with.
In my experience, on 3D approaches, it´s usually not the ceiling that surprises me, it´s the actual low visibility.
On that I believe we can fully agree. The issue is not really how low you can go before becoming visual, it what you can see once the visual segment begins.
Emir wrote:
I did few ILS approaches in real IMC to DH 200-ish ft with visibility ranging from 2 to 5 km and you’re surprisingly low when you pop out of the cloud. Thinking about doing non-precision approach to even 100 ft higher, I don’t feel like I’d do that
Perfect example of personal risk management, based on operational experience. This may change in one direction or the other with additional experience. The blokes at EASA formulating policies and procedures are only as good as the information they base themselves on. Pilot licenses comes with privileges and obligations. Nothing stops us from having our own (higher) limits, based on whatever seems right.
In my experience, on 3D approaches, it´s usually not the ceiling that surprises me, it´s the actual low visibility. So, come back here when you´ve done some 3D approaches in low vis RVR 550M and we´ll chat again. ;-)
One of the most common “mistakes” I see, even with experiences professional pilots, are where their eyes are pointing when looking out for the references before the minimum, and secondly, in multi pilot environments, having briefed and understood who´s looking in and who´s looks out from minimums +100. Who calls what. Anways, the SOP “should” theoretically (and often practically) handles that.
Interestingly on the approach that you mentioned the vis requirement is also less than that for the ILS! 900M RVR on a 2D approach, even with HIALS. Yikes.
Yeager wrote:
Exposure and experience dictates, or should, your personal (higher) minima´s.
I did few ILS approaches in real IMC to DH 200-ish ft with visibility ranging from 2 to 5 km and you’re surprisingly low 
when you pop out of the cloud. Thinking about doing non-precision approach to even 100 ft higher, I don’t feel like I’d do that.
Airborne_Again wrote:
Actually it can. EASA does state that “It cannot be expected that each operator is able to conduct similar safety assessments, and this is not necessary.”
That is not a blank statement.
It´s subject to the operator using the data provided by other operators having performed the analyses (successfully) of the approach for the 2D approach to DA, as referenced in the GM.
Airborne_Again wrote:
I don’t think this is pushing anything to the limit more than flying a regular ILS or LPV to minimums.
I think it is. With the 3D approach, as opposed to the 2D (eg. LOC only), you have approved precision vertical guidance and as an overall better operational protection from (lower RNP requirements during the approach to land phase) and are more likely to be arriving at the “correct” DA, than that of a less precise CDFA (2D, eg. LOC only) approach. No way that I would be as comfortable doing even, say, an autopilot coupled 2D approach vs. a manual uncoupled 3D approach to the same runway.
Additionally. One thing is what´s legally acceptable and another is what your personal perception of the operational equipment and environment actually is. Exposure and experience dictates, or should, your personal (higher) minima´s.
Yeager wrote:
Great blog – well done! I Great summery, thanks for sharing!
Thanks!
this is subject to the conditional compliance with the GM (analysis requirements), and of course this could include assessments already performed by other parties
So, without any specific assessment (self or by third party), the DA shall not be used without an addition to it (derived DA).
Actually it can. EASA does state that “It cannot be expected that each operator is able to conduct similar safety assessments, and this is not necessary.”
I wonder if many CAT or NCC operations actually push it to the limit, by using uncorrected DA with CDFA.
I don’t think this is pushing anything to the limit more than flying a regular ILS or LPV to minimums.
Airborne_Again wrote:
There is no reason to have any such addition to the DA. See my blog post here: https://www.aglarond.se/wordpress/add-on-to-the-da-of-a-cdfa/
Great blog – well done! I Great summery, thanks for sharing!
My remarks follows.
I would say that there are reasons why the regular Joe should us a derived DA, by adding eg. 50FT, to assure not descending below the MDA(H).
As your blog states. Some aviation authorities have questioned a sound justification, allowing for descend below the MDA(H), while using an uncorrected DA.
NCO.OP.111(a) “allows” for the brief descend below the DA (flown as CDFA), but this is subject to the conditional compliance with the GM (analysis requirements), and of course this could include assessments already performed by other parties. So, without any specific assessment (self or by third party), the DA shall not be used without an addition to it (derived DA). Note 1 on the Jepp chart sort highlight this awareness.
After reading your blog describing the rational behind allowing for an uncorrected DA, I would still adhere to adding 50ft, since I don´t know where to find details of any other “operator” having performed the required analyses as per your references. You can then call that my personal 2D minima.
Airborne_Again wrote:
That some operators choose to have such an addition anyway is a different matter.
I wonder if many CAT or NCC operations actually push it to the limit, by using uncorrected DA with CDFA. Clearly this depends on the regularity of airport usage and and low weather statistics. I don´t know of any, but I´m limited in my general insight of operators. Certainly the CAT and NCC operations I´ve been with, all have had the addition of 50ft or 60ft in for operational use.
Yeager wrote:
The LOC only, when flown as CDFA, should be used with an operators addition to the DA (commonly 50 FT additive) and you get a derived DA+50FT (in reality you DA is now 50 feet higher than depicted as DA for the LOC only approach).
There is no reason to have any such addition to the DA. See my blog post here: https://www.aglarond.se/wordpress/add-on-to-the-da-of-a-cdfa/
That some operators choose to have such an addition anyway is a different matter.
Emir wrote:
and how LOC (GS out) approach has almost same or lower minima than ILS
When comparing the ILS DA with the LOC (DA/MDA(H)) with the same 2.5% missed app.clb. gradient:
The ILS approach with the “higher” DA allows for pilot decision to continue or go around AT the depicted DA, and allows (by design) for a further altitude loss (below the DA) before entering the missed approach climb segment.
The LOC only approach will be flown either as CDFA with derived DA or with a hard MDA(H) (level off = not descending below)
The LOC only, when flown as CDFA, should be used with an operators addition to the DA (commonly 50 FT additive) and you get a derived DA+50FT (in reality you DA is now 50 feet higher than depicted as DA for the LOC only approach). Looking at the aircraft approach cat A your derived DA on this approach should be 1510+50FT=1560FT(which similar to the ILS approach allows for an altitude loss before entering the missed approach climb segment).
In other words, the ILS minima (cat A) is 1534FT vs LOC only minima (cat A) derived DA is 1560FT = higher LOC minima than ILS. This is for a CDFA approach type.
If you feel like pushing it to the limit, you could skip the CDFA and dip down after 3.9NM SG to the MDA of 1510FT and continue to the defined MaP at 0.7NM SG. This approach would not allow for any descend below 1510FT (as your using and MDA). It´s a theoretical consideration, I´d be hard pressed to consider it.
The Jepp chart (11-1) has a note 1 regarding operators using LOC DA instead of MDA.
If you look in the Operators Manual (OM) part B, of the operator where you´re doing your Saab 340 Type Rating, you should find a Reference Table showing the DA addition(s) for 2D approaches or some other Operators Procedure for 2D (LOC etc.) approaches. Find below attached an example of an operators reference table.
Have fun.
