Huh? I've always been taught it's the pilot. As in *flight* visibility (ASOS is ground vis).
Anyone have an actual reference, either way?
Try this section for the flight visibility.
Section 91.155: Basic VFR weather minimums.
(a) Except as provided in paragraph (b) of this section and §91.157, no person may operate an aircraft under VFR when the
flight visibility is less, or at a distance from clouds that is less, than that prescribed for the corresponding altitude and class of airspace in the following table:
Airspace Flight visibility Distance from clouds
Class A Not Applicable Not Applicable.
Class B 3 statute miles Clear of Clouds.
Class C 3 statute miles 500 feet below.
1,000 feet above.
2,000 feet horizontal.
Class D 3 statute miles 500 feet below.
1,000 feet above.
2,000 feet horizontal.
Class E:
Less than 10,000 feet MSL 3 statute miles 500 feet below.
1,000 feet above.
2,000 feet horizontal
At or above 10,000 feet MSL 5 statute miles 1,000 feet below.
1,000 feet above.
1 statute mile horizontal.
Class G:
1,200 feet or less above the surface (regardless of MSL altitude)
Day, except as provided in §91.155(b) 1 statute mile Clear of clouds.
Night, except as provided in §91.155(b) 3 statute miles 500 feet below.
1,000 feet above.
2,000 feet horizontal.
More than 1,200 feet above the surface but less than 10,000 feet MSL
Day 1 statute mile 500 feet below.
1,000 feet above.
2,000 feet horizontal.
Night 3 statute miles 500 feet below.
1,000 feet above.
2,000 feet horizontal.
More than 1,200 feet above the surface and at or above 10,000 feet MSL 5 statute miles 1,000 feet below.
1,000 feet above.
1 statute mile horizontal.
Section 91.175: Takeoff and landing under IFR.
(a) Instrument approaches to civil airports. Unless otherwise authorized by the FAA, when it is necessary to use an instrument approach to a civil airport, each person operating an aircraft must use a standard instrument approach procedure prescribed in part 97 of this chapter for that airport. This paragraph does not apply to United States military aircraft.
(b) Authorized DA/DH or MDA. For the purpose of this section, when the approach procedure being used provides for and requires the use of a DA/DH or MDA, the authorized DA/DH or MDA is the highest of the following:
(1) The DA/DH or MDA prescribed by the approach procedure.
(2) The DA/DH or MDA prescribed for the pilot in command.
(3) The DA/DH or MDA appropriate for the aircraft equipment available and used during the approach.
(c) Operation below DA/ DH or MDA. Except as provided in paragraph (l) of this section, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—
(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;
(2) The
flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and
(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:
(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.
(ii) The threshold.
(iii) The threshold markings.
(iv) The threshold lights.
(v) The runway end identifier lights.
(vi) The visual approach slope indicator.
(vii) The touchdown zone or touchdown zone markings.
(viii) The touchdown zone lights.
(ix) The runway or runway markings.
(x) The runway lights.
(d) Landing. No pilot operating an aircraft, except a military aircraft of the United States, may land that aircraft when—
(1) For operations conducted under paragraph (l) of this section, the requirements of (l)(4) of this section are not met; or
(2) For all other part 91 operations and parts 121, 125, 129, and 135 operations, the
flight visibility is less than the visibility prescribed in the standard instrument approach procedure being used.
(e) Missed approach procedures. Each pilot operating an aircraft, except a military aircraft of the United States, shall immediately execute an appropriate missed approach procedure when either of the following conditions exist:
(1) Whenever operating an aircraft pursuant to paragraph (c) or (l) of this section and the requirements of that paragraph are not met at either of the following times:
(i) When the aircraft is being operated below MDA; or
(ii) Upon arrival at the missed approach point, including a DA/DH where a DA/DH is specified and its use is required, and at any time after that until touchdown.
(2) Whenever an identifiable part of the airport is not distinctly visible to the pilot during a circling maneuver at or above MDA, unless the inability to see an identifiable part of the airport results only from a normal bank of the aircraft during the circling approach.
