BE36 pilot had inaccurate WX reported by automated ASOS system.

Attributes
ACN	488938
Time
Date	200010
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : pln.airport
State Reference	MI
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Weather Elements	other
Light	Night
Aircraft 1
Controlling Facilities	artcc : zmp.artcc tower : bos.tower
Operator	general aviation : personal
Make Model Name	Bonanza 36
Operating Under FAR Part	Part 91
Flight Phase	climbout : initial ground : taxi ground : takeoff roll
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : cfi pilot : atp pilot : multi engine
Experience	flight time last 90 days : 30 flight time total : 6000 flight time type : 30
ASRS Report	488938
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	inflight encounter : weather inflight encounter other other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact none taken : anomaly accepted
Supplementary
Problem Areas	Weather FAA
Primary Problem	FAA

Narrative:

At about XA00 I canceled an IFR flight plan 7 mi southwest of pellston airport, and landed VFR. After staying long enough to call lan FSS and file an IFR flight plan, I taxied out and departed VFR and picked up my IFR clearance with ZMP. On departure, I noticed a scattered layer of clouds over the northeast corner of the airport. Later I contacted the FSS and checked the ASOS reports. Around this time the ASOS was reporting 400 ft scattered. 9 mins later, it was reporting 400 ft broken. This leaves the possibility that a pilot could be in class east airspace VFR one min and when the ASOS goes from scattered to broken the pilot could be in class east airspace with no IFR clearance. It would be helpful at these type airports if the ASOS were broadcast on a local frequency. It has been my experience that automated WX observation system can be grossly inaccurate. Other pilots I have talked to and some FSS personnel have spoken with have had the same experience with these system.

Original NASA ASRS Text

Title: BE36 PLT HAD INACCURATE WX RPTED BY AUTOMATED ASOS SYS.

Narrative: AT ABOUT XA00 I CANCELED AN IFR FLT PLAN 7 MI SW OF PELLSTON ARPT, AND LANDED VFR. AFTER STAYING LONG ENOUGH TO CALL LAN FSS AND FILE AN IFR FLT PLAN, I TAXIED OUT AND DEPARTED VFR AND PICKED UP MY IFR CLRNC WITH ZMP. ON DEP, I NOTICED A SCATTERED LAYER OF CLOUDS OVER THE NE CORNER OF THE ARPT. LATER I CONTACTED THE FSS AND CHKED THE ASOS RPTS. AROUND THIS TIME THE ASOS WAS RPTING 400 FT SCATTERED. 9 MINS LATER, IT WAS RPTING 400 FT BROKEN. THIS LEAVES THE POSSIBILITY THAT A PLT COULD BE IN CLASS E AIRSPACE VFR ONE MIN AND WHEN THE ASOS GOES FROM SCATTERED TO BROKEN THE PLT COULD BE IN CLASS E AIRSPACE WITH NO IFR CLRNC. IT WOULD BE HELPFUL AT THESE TYPE ARPTS IF THE ASOS WERE BROADCAST ON A LCL FREQ. IT HAS BEEN MY EXPERIENCE THAT AUTOMATED WX OBSERVATION SYS CAN BE GROSSLY INACCURATE. OTHER PLTS I HAVE TALKED TO AND SOME FSS PERSONNEL HAVE SPOKEN WITH HAVE HAD THE SAME EXPERIENCE WITH THESE SYS.

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.