I deleted the first question after it was answered
Why? I'm left scratching my head when people do this. Not trying to bust your balls here, but doing that removes whatever your first question was from hte forum. Now, if somone else was wondering the same thing, they'll have to ask the same question, instead of being able to read the thread.
Anyway, about your question on wx andthe FAF. You've pretty much got your answer, but let me add a little that may make it clearer, and will help you later when sorting out other regulatory questions.
You ask:
where in the regs does it say you can continue the approach if the visiblity drops after you cross the FAF
That's the wrong question, regulations very rarely tell you what you
may do, they almost always tell you what you
may not do. In the instances where a regulation tells you you may do something it is almost always because some other regulation would otherwise prohibiit it.
You
should be asking:
where in the regulations does it say that you cannot continue past the FAF, unless the visibility is above minimums.
Then the answer is easy; nowhere. You said yourself that you've examined 91.175 with a microscope. You couldn't find anything, other then hte requirement to have flight visibility above the minimums in order to descend below MDA/DH , so if there isn't a requirement to have minimum vis before proceeding past the faf, then it's perfectly legal to do so.
Do you see the difference between wondering where it says you *can* do something and wondering where it says you *can't* do something?
Anyway, under part 91, you don't need any visibillity to begin or continue an approach, except for continuing bleow MDA/DH. It is perfectly legal to begin an approach and continue the approach right down to MDA/DH with visibility reported zero. It's legal, because there's nothing in part 91 which prohibits it. (it would be in 91.175 if it existed)
Now a couple of things to further clarify. In order to descend below MDA/DH, you must have the minimum
flight visibility. It's important to understand that it's
flight visibility, and flight visibility can only be determined by the pilot. I have included an FAA Chief Counsel interpretation below which addresses the issue of flight visibility vs reported visibility. Note also that it says Flight Visivbility takes precedence over RVR.
Now, so far the discussion has been for Part 91 only. Thngs are a bit different if you are flying under Part 121 or Part 135 (although ultimately the answer is the same)
Under part 135 you may not begin an approach unless the required weather minimums are reported, 135.225(a)
And under Part 121 you may not proceed past the FAF unless the visibility is reported above the minimum visibility 121.651(b)
However, under both 121 and 135, you are allowed to continue if you are already inside the FAF and a new report shows the vis below minimums. 121.651(c) and 135.225(c)
Ok, this is an example of what I mentioned earlier. 135.225(c) and 121.651(c) tell you that you
may do something, but that is only because that action is prohibited elsewhere (in 135.225(a) and 121.651(b) respectively)
Hope that this helps, and that you aren't just more deeply confused.
FAA Legal Interpretation:
March 10, 1986
Mr. Larry K. Johnson
Dear Mr. Johnson:
This is in response to your letter of February 6 requesting an interpretation of Federal Aviation Regulation (FAR) Part 91, Section 91.116.
Specifically, you request clarification of the term "flight visibility" in connection with the requirement in FAR 91.116(c) that an aircraft not be operated below a published decision height or minimum descent altitude if the flight visibility is less than the visibility prescribed in the standard instrument approach procedure being used. The question arises as to whether descent below the DH or MDA can be made when the runway visual range (RVR) is reported at less than the published minimum RVR for the approach but the flight visibility is greater than that minimum.
The flight visibility is controlling. If the flight visibility exceeds the published minimum for the approach, than the pilot may proceed as long as the other requirements of paragraph 91.116(c) are met regardless of the reported RVR. The National Transportation Safety Board (NTSB) has upheld this interpretation in several enforcement cases. However, the pilot's judgment of flight visibility is not necessarily conclusive if there is a question as to the actual flight visibility conditions at the time of the approach. Reported visibility and other evidence of record may be considered by the Federal Aviation Administration and the NTSB in determining the actual flight visibility.
Enforcement action would be taken only in those cases in which the pilot could not reasonably conclude that flight visibility was at or above approach minimums, but the pilot nevertheless proceeded to land or descent below DH or MDA.
Sincerely, David L. Bennett
Manager, Airspace and Air Traffic Law Branch
Regulations and Enforcement Division
