Scenario 1: Pilot is under IFR and descends as allowed to a lower altitude placing him in VMC. It's hazy but visibility is 4-5 miles by his determination and he's well under the base by the required 500 feet. He has good ground contact as he flies over the airport on the outbound leg of his VOR approach. He contacts the TRACON or ARTCC as appropriate and request a visual approach for the airport. However, the AWOS for his intended field is reporting less than VFR on visibility only. The sky is clear. The controller sees this and reasonably refuses to authorize the visual approach as it's him also on the line here. The pilot may cancel IFR and continue to the airport under VFR provided he does indeed observe the VFR minimums required. He's perfectly legal to do so.
No, he's not. 14 CFR 91.155(d)(1) requires GROUND visibility of at least 3 statute miles, and 14 CFR 1.1 clearly defines who can determine ground visibility, and it ain't the pilot.
Scenario 2: The sky is clear but visibility is hanging around 4-5 miles. A pilot is approaching from nearby airport. He sees the lower visibility but determines it's high enough for him to safely land and does so. By the way, he has no radio so no weather information is received from an AWOS. He's also perfectly legal.
No, he's not either, and for the same reason.
So... Where in the following is it indicated the source of the the data must be an ASOS, AWOS or ATIS? That seems to be the assumption here.
It doesn't say ASOS, AWOS, or ATIS. It says "as reported by the United States National Weather Service or an accredited observer." See the definitions of flight and ground visibility from 14 CFR 1.1 that I posted earlier.
It can be strictly pilot observation.
No, it can't.
Is the controller going to refuse to allow the pilot to cancel IFR? I doubt it.
No. But as soon as the pilot cancels IFR, he assumes responsibility for maintaining VFR minimums, and if he lands, he has busted 91.155(d)(1).
The now VFR pilot may descend and take a look-see just as the following pilot can.
He can take a look-see all day long, but as soon as he enters the pattern or wheels hit the ground, it's a bust.
Is the NORDO VFR pilot going to call ahead? Even if he did, perhaps the temperature decreased the spread so visibility decreased while en route. It's not illegal for him to look at the circumstance and determine one, if it's legal; two, if it's safe; three, is it within his personal minimums?
It is illegal. If you disagree, show me where lack of radios exempts you from 91.155.
As for how to tell - Someone mentioned the ASOS turning on the beacon automatically. I know that is what the tower does at the home drome when the field goes IFR.
BTW, I've also had this situation happen at a class C, and the same rules apply. I had taken off from RYV and I could see the field, and the runway, from over 20 miles away. But, fog was rolling in and had covered the ASOS after I listened to ATIS (and they were cutting a new ATIS while I called Approach). Approach said "The field just went IFR, say intentions." I reported that I had the field in sight, but the controller again stated "The field is IFR." So I requested a pop-up clearance and shot the ILS. On final, Tower advised "RVR 2400, rollout 6000." I was in clear air the whole way down.
Now I realize that controller did me a favor.