Hi All.
I'm trying to get some more understanding of how a pilot determines if they have the legal visibility min on an approach. both for controlled and non controlled airfields.
I have an instructor saying that I should work out, before I fly, what to expect to see at the destination airport. EG if an ILS min is 250ft and 0.8km vis, then what lights will I see at that height? They said, I should be looking at the distance from the threshold, for that min height and then calculating what lights I will see, based on the distance between lights and the planes distance from the threshold.
If I'm approaching an uncontrolled airfield, with an RNP or other aid, then I use the distance between the runway edge lighting, listed in ERSA, to calculate what number of lights I will see, at the min altitude, to determine if the required vis is met.
Another instructor has said, this is too much airline thinking and another that says all I need to see is the PAPI's for non precision approached and at least 1 light for precision approaches. I can't find any AIP, or other reference for this statement.
Any help on if this is necessary and how to do it?
There surely should be a little room for discretion. Doing an ILS or vnav into a busy controlled aerodrome and you decide to do a missed approach with visibility of 1000m. That's longer than the entire runway at most country aerodromes. The tower would be unimpressed...
That's what I would have thought. Maybe the instructor telling me all this, was just trying to get me to think.
The guy in the linked article below put its this way. You're the only one who knows what they saw, so don't dob yourself in, so to speak, if an inspector questions you.
Hello,
I think you have to determining legal visibility for approaches involves anticipating what lights will be visible at specified minimums, using approach lighting system specifications and distances from the runway threshold. For uncontrolled airfields, visibility is calculated based on the number of visible runway edge lights at minimum descent altitude from sources like ERSA.
