Landing in mist - Minimums respected?

Well its quite complex so I do understand they leave it up to the operator. I believe LIDO is customizable to the operators needs (its what I’ve heard, I never used LIDO myself), also Navblue is customizable to the operators needs, we had our departure procedure in case of engine failure directly on our departure plates for example, maybe there is also an option to have the minima adjusted to the operators needs but it will probably cost money.

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There is more to it obviously, in Europe the eAIP charts only show the OCA/H. If you compare the eAIP charts with the Navblue and Jeppesen charts you can see that the OCA/H are directly copied for precision and for non-precision approach. For precision approach the OCA/H DOES include a height loss correction whereas the non-precision approach OCA/H does not.

Traditionally non-precision approaches where flown non-CDFA (Continuous Descent Final Approach) where you would descent to the MDA/H, level off and fly to the Missed-approach point which is a DME distance, beacon or marker, then decide to either go-around or continue for landing, like this:

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The industry has moved away from non-CDFA approaches and non-precision approaches are therefore flown as CDFA nowadays without level-off, it didn’t make sense anyway to level-off with a big jet and fly level at a few hundred feet and then try to land if runway was insight at the missed-approach point. Note that there is no guarantee that the aircraft is even in a position to land at the MAPt, just see where the missed-approach point is located in the above approach (runway threshold), no way you will be able to land safely when runway is insight at the threshold at 740 ft above ground :joy: :joy: :joy:.

So even before non-CDFAs were largely abandoned most operators already flew a 3 degree glidepath to the MDA + height loss correction or MAPt whichever occurs first and then performed a go-around. Its also not exactly in line with the “stabilized” approach concept either to level of your large jet at a few hundred feet and fly level, then cut the power and continue descent. Some non-CDFAs still exist today, for example procedures based on only one beacon and no DME often have a non-CDFA design (there isn’t really another way), nowadays most planes can fly RNP approaches of course so its not often flown operationally. We are not even allowed to fly a non-precision approach non-CDFA (company procedure).

The same approach now looks like this:

Sorry for the long essay, but the point I’m trying to make is that the way OCA/H were determined for non-precision approaches (as a MDA/H without height-loss correction) did make sense in the past but with the abandonment of non-CDFA approaches it doesn’t make sense anymore and unless the state publishes a OCA/H including heigh-loss correction for non-precision approaches, companies like Navblue and Jeppesen just copy the OCA/H and leave it up to the operator. Which doesn’t explain why Jeppesen calls it a DA/H, that just stupid for the lack of a better word and causes a lot of confusion amongst pilots.

Contrary to what I said before, APV approaches do seem to have a heigh-loss correction added to the OCA/H and therefore can be used as DA/H directly. So only for non-precision approaches (VOR / NDB / LNAV / LP) this height-loss correction needs to be applied if not applied by the state. For APV (Approach with Vertical Guidance such as LNAV / VNAV and LPV) and precision approaches (ILS, MLS, GLS) this is already included:

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Haha. Thanks for the extensive info. It’s interesting, especially since I want to fly as close to reality as possible.

I have not focused on missed approach procedures yet so I currently have no other option then to land, no matter what :smiley: But it’s good to know the rules, even when you break them.

Hi. Also from my side. Thank you so much for the details and the explanation. Very nice.

One question to the second picture from the top, which explains OCA, DA, MDA etc. - the left portion for precision approach is clear. The right side I struggle with as it suggests that the Lower Limit / Margin can actually be below MDA (but above OCA). I thought that MDA is not to be exceeded and therefore the DA includes a margin to account for aircraft performance, downdrafts etc? Or does my confusion stem from that Jeopesen sets MDA equal to OCA?

Thanks in advance.

The lower limit is defined by the system minima I believe, for example I came across an ILS chart form the AIP which showed an OCA of 170 ft for an ILS approach which is below the ILS CAT I lower limit of 200 ft.

Ah so the Lower Limit as depicted above doesn’t have anything to do with the DA (for non precision approach), which needs to be above MDA. And the DA is determined by aircrew / company policy depending on performance, wind shear etc. ?

What confused me that the box Lower Limit seems to suggest Aircraft Performance as factors of consideration when determining this Lower Limit, which according to the drawing can be below (and not above) MDA.

Well it has something to do with it, the OCA/H does take into account obstacles in an area of which the size depends on the accuracy of the approach + a margin + height loss in case of precision approach and all the other factors but it does not take into account the lower limit of the approach aid, for example 200 ft for a CAT I ILS, 100 ft for a CAT II ILS, so if there are no obstacles the OCA/H can be very low, the DA or MDA in such case is the higher of the OCA/H or system limit.

For example this ILS approach has a OCA/H of 170 ft above the threshold (CAT A):

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So the eventual minima (Navblue) becomes as below (not below 200 ft for a CAT I ILS), that is how three categories end up with the same minima all of a sudden:

You can see that Navblue (Jeppesen same same) takes the system minima or OCA/H, whichever is higher and thus does not go below 200 ft above threshold for a CAT I ILS. Also note that the minima for the LOC + DME approach is exactly copied over, this is a non-precision approach so there is no height-loss correction in the OCA/H, therefore to use this as a DA/H you need to add a height-loss correction. As you can see, Navblue does not specify what kind of minima (DA or MDA) these are, I assume to prevent confusion, Jeppesen would call everything DA/H (except circling minima).

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