Originally Posted by
cougar
From the references above, flight visibility is not approach visibility. On approaches with a DA/DH, where a decision is being made, once established on the final segment, the approach may be continued even when the reported WX vis is below the published approach mins. Once at DA/DH(or MDA), as long as any approach lights are in sight the approach may continue. At 100' the lighting listed in 91.175 (c) must be in sight.
As a rule we would teach, at MDA/DA any lights, at 100' must see colored lights to continue.
I agree with this above with the exception of RVR for air carriers. Most air carriers have ops specs that specifically state "TDZ RVR is controlling (if available)" meaning that even though the "flight visibility" may very well be met when you arrive at DA/DH, because the RVR is below what the FAA determines to be safe, you may not continue (or even start the approach if not yet beyond the FAF/FA Point).
GA/Part 91 world, flight visibility = visibility out the window and nobody knows that except the pilots. As someone stated before, if SFC Vis and/or RVR are both WAY below the min flight vis required, you may have a hard time defending your decision to continue during an enforcement action but according to the letter or the law, it is legal IF you actually had the min flight vis. Unfortunately, when it comes to this type of "gray area", it's not 100% what was legal to the T, but more about what you can prove / defend / justify when brought in to a hearing during a possible enforcement action. A good general rule for pilots... C.Y.A. and don't be stupid.
Common Example: If the runway is 10,000 ft long and the departure end (where the visibility sensor is) is <1/4 SM and you have the approach end in sight 10 miles out where a fog bank, quite literally, splits the runway (Oregon coast during the spring and fall!!!)... I'd say you're fine.