What are reasonable visibility minima for daytime approach to, and take-off from, an IFR runway whose complete lighting system (approach lights and runway lights) is inoperative? I’m trying to decide beforehand, the threshold below which I will rather go to the (more expensive) alternate. I’ll have to decide before going there depending on latest forecast, so that I’m not stuck there after landing :)
The context is LKVO.
One end has an ILS approach with a 150ft OCA, meaning a 200ft DH (system minima), so on the GS I should be at the DH at 1165m from the threshold, so taking some buffer above that should be workable? The same value looks OK as take-off minima, it is significantly more than my ground run or TODR (take-off distance required, to 50ft) or ASD (accelerate-stop distance ). Unless the legal minimum is higher? If I understand the GM4 NCO.OP.110 tables 2 and 3A correctly, the legal minimum is 1200m.
The other end has an LPV approach with 300ft OCA/DH, which gives 1750m, so again rounding that up to maybe 2000m is reasonable? The legal minimum seems to be 1400 m, which looks like I won’t see the runway at DH…
I don’t know the legal position (other than what it says on the Jepp plate) but a departure below 400m vis gets progressively more and more “interesting”, and 200m gets really quite interesting, with the picture being almost unchanging except for the ASI slowly moving and then at say 70kt you pull back and everything disappears and an instant transition to the AI is crucial.
In the US, with a DH of 200, the minimum visibility is 0.5 SM.which is 805 meters. When the ALS is OOS, the visibility requirement increases to 0.75 SM or 1207 meters. The distance at DH to the threshold is 1164 meters if I did my math correctly. At 300 ft DH, the distance to the runway increases to 1746 meters, so one would need to have at least this visibility to expect to be able to see the runway at DH.
The whole thing is based on the common sense approach that you need to see the runway environment at the point you make the decision to land or go around. In the case of CAT1 ILS or LPV this will be the approach light system. A CAT3A approach has no need of an approach light system as at the 50 ft DH the approach lights are behind you and all you will see is the runway lights.
With the CAT3B no DH landing you might get a glimpse at the runway centreline lighting as you tightly grip the seat cushion.
@lionel I’d read it as you continue approach below DH if you see runway, or runway marking, or etc., but the legal min RVR is 1400. Even if you use the formula in PART NCO, Table 3.A: CAT I, APV, NPA (aeroplanes, Minimum and maximum applicable RVR/CMV (lower and upper cut-off limits)) specifically says for ILS, MLS, GLS, PAR, GNSS/SBAS, GNSS/VNAV that Legal MAX is 1500m, if I read it correctly.
I’m not sure if most people missed the point of the question (being what are the “reasonable” or “sensible” minima; are those higher than the legal ones?), or if everybody is implicitly saying that the legal minima are reasonable and sensible (or, at least, they are not too low).
A_and_C wrote:
The whole thing is based on the common sense approach that you need to see the runway environment at the point you make the decision to land or go around.
A_and_C wrote:
In the case of CAT1 ILS or LPV this will be the approach light system.
This thread is explicitly about the ALS being inoperative. Implicitly (I forgot to mention it), about light GA, so CAT2 / CAT3 are out of scope of the discussion :)
lionel wrote:
One end has an ILS approach with a 150ft OCA, meaning a 200ft DH (system minima), so on the GS I should be at the DH at 1165m from the threshold, so taking some buffer above that should be workable?
I remember the GS leads to the touchdown zone which is 300m into the runway, so actually the threshold is 300m closer. The legal minimum seems not so bad.
lionel wrote:
The same value looks OK as take-off minima
I would not worry at all about the take off regarding the lighting. In my experience if you can see the runway center line you are fine without any lights. If you need the center line lights (not available on all IFR runways) you are probably down to 200m or so and in real trouble to even find the right runway. So I would just use the legal minimum.
Sebastian_G wrote:
I remember the GS leads to the touchdown zone which is 300m into the runway, so actually the threshold is 300m closer. The legal minimum seems not so bad.
Good point. I had not thought of that. Thanks.
lionel wrote:
I’m not sure if most people missed the point of the question (being what are the “reasonable” or “sensible” minima; are those higher than the legal ones?), or if everybody is implicitly saying that the legal minima are reasonable and sensible (or, at least, they are not too low).
Your comment reveals a major flaw with the way that we use AOM.
The atmosphere is not homogeneous. Comparing the reported RVR with the minimum from table 2 is not a deterministic calculation. It is a diagnostic, that comes with both false negatives and false positives, that was set to reduce the probability of a go around at that minimum RVR to 5% or below. If the RVR is in a sensible ballpark, I would fly the approach with the expectation that I might need to go around. FWIW, I don’t believe that Guidance Material to NCO.OP.110 establishes “legal minima”. Unless the state establishes minima for LKVO, you can pick your own sensible RVR above 550 m.
By contrast, for fuel planning purposes, I wouldn’t rely on completing that approach with a forecast vis less than about 2000 m, perhaps more.
bookworm wrote:
I don’t believe that Guidance Material to NCO.OP.110 establishes “legal minima”.
@bookworm, am I right that you are somewhat responsible for changing that?
I noticed that one of the changes in NPA 2020-02 is that approach visibility minima will be AMC, which to the GA pilot definitely constitutes “legal minima”, unless you produce an AltMoC and have it approved.
So, while those minima may not be binding as of now, they will, in all probability, be law in a few months?
