Reporter did not recognize ground fog at night and canceled IFR and went IMC on short final.

Attributes
ACN	285657
Time
Date	199409
Day	Wed
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : mmi
State Reference	TN
Altitude	agl bound lower : 200 agl bound upper : 400
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : bna
Operator	common carrier : air taxi
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 135
Flight Phase	landing : missed approach landing other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 4300 flight time type : 250
ASRS Report	285657
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	inflight encounter : weather inflight encounter : vfr in imc non adherence : clearance
Independent Detector	other other : unspecified cockpit
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

The WX was severe clear, 20 mi visibility. I had the beacon in sight (pre dawn), AWOS reporting 200 ft overcast visibility 1/2 mi. I was talking to bna approach. Everywhere within 75 NM was clear, visibility unrestr. With the beacon in sight at 15 mi, I also had the REIL and the runway lights. I thought for sure the AWOS machine had gone nutty. I canceled IFR, proceeded to the field VFR. Overflew the field. There was a thin layer of haze over the airport. I had been airborne almost 7 hours 15 mins and was tired but was absolutely sure the AWOS was mistaken the field good VFR. Downwind to base aok, final approach all was ok, everything still in sight. Then all went black, all visual contact lost. Back on instruments for a second at 300- 400 ft AGL. Lights in sight but very hazy. I initiated a go around with loss of all VMC on climb for 200 ft or so. Then VMC 20 mi visibility and airport environment in sight. I notified bna that I would proceed northeast 15 mi to mnv VFR and advised them of what happened. He remarked 'you were cleared VFR approach.' later that morning a man at mnv advised me 'in the fall airport a is clear, 10 mi down airport B socked in zero zero. The mountain airports can be tricky.' from now on I will heed the AWOS tape no matter what it looks like from the air during night operations.

Original NASA ASRS Text

Title: RPTR DID NOT RECOGNIZE GND FOG AT NIGHT AND CANCELED IFR AND WENT IMC ON SHORT FINAL.

Narrative: THE WX WAS SEVERE CLR, 20 MI VISIBILITY. I HAD THE BEACON IN SIGHT (PRE DAWN), AWOS RPTING 200 FT OVCST VISIBILITY 1/2 MI. I WAS TALKING TO BNA APCH. EVERYWHERE WITHIN 75 NM WAS CLR, VISIBILITY UNRESTR. WITH THE BEACON IN SIGHT AT 15 MI, I ALSO HAD THE REIL AND THE RWY LIGHTS. I THOUGHT FOR SURE THE AWOS MACHINE HAD GONE NUTTY. I CANCELED IFR, PROCEEDED TO THE FIELD VFR. OVERFLEW THE FIELD. THERE WAS A THIN LAYER OF HAZE OVER THE ARPT. I HAD BEEN AIRBORNE ALMOST 7 HRS 15 MINS AND WAS TIRED BUT WAS ABSOLUTELY SURE THE AWOS WAS MISTAKEN THE FIELD GOOD VFR. DOWNWIND TO BASE AOK, FINAL APCH ALL WAS OK, EVERYTHING STILL IN SIGHT. THEN ALL WENT BLACK, ALL VISUAL CONTACT LOST. BACK ON INSTS FOR A SECOND AT 300- 400 FT AGL. LIGHTS IN SIGHT BUT VERY HAZY. I INITIATED A GAR WITH LOSS OF ALL VMC ON CLB FOR 200 FT OR SO. THEN VMC 20 MI VISIBILITY AND ARPT ENVIRONMENT IN SIGHT. I NOTIFIED BNA THAT I WOULD PROCEED NE 15 MI TO MNV VFR AND ADVISED THEM OF WHAT HAPPENED. HE REMARKED 'YOU WERE CLRED VFR APCH.' LATER THAT MORNING A MAN AT MNV ADVISED ME 'IN THE FALL ARPT A IS CLR, 10 MI DOWN ARPT B SOCKED IN ZERO ZERO. THE MOUNTAIN ARPTS CAN BE TRICKY.' FROM NOW ON I WILL HEED THE AWOS TAPE NO MATTER WHAT IT LOOKS LIKE FROM THE AIR DURING NIGHT OPS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.