Govt pilot complains of the lack of accuracy of the AWOS system.

Attributes
ACN	288653
Time
Date	199411
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : hef
State Reference	VA
Altitude	agl bound lower : 500 agl bound upper : 500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : hef tower : cha
Operator	other
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	other : unknown
Flight Phase	climbout : initial climbout : takeoff ground other : taxi
Flight Plan	None
Person 1
Affiliation	government other
Function	flight crew : single pilot
Qualification	pilot : cfi pilot : instrument pilot : commercial
Experience	flight time last 90 days : 25 flight time total : 2675 flight time type : 25
ASRS Report	288653
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	inflight encounter : weather other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

The flight was for takeoff and landing practice. The AWOS at manassas, va, was reporting 1900 ft overcast and 10 mi visibility. The AWOS was checked just prior to taking the active runway. Once airborne, it was obvious that the WX was not equal to the AWOS report. The actual WX was approximately 1200 ft overcast and 4 mi visibility. Caution should be taken when using AWOS reports. Recognize their limitations and possibility of errors.

Original NASA ASRS Text

Title: GOVT PLT COMPLAINS OF THE LACK OF ACCURACY OF THE AWOS SYS.

Narrative: THE FLT WAS FOR TKOF AND LNDG PRACTICE. THE AWOS AT MANASSAS, VA, WAS RPTING 1900 FT OVCST AND 10 MI VISIBILITY. THE AWOS WAS CHKED JUST PRIOR TO TAKING THE ACTIVE RWY. ONCE AIRBORNE, IT WAS OBVIOUS THAT THE WX WAS NOT EQUAL TO THE AWOS RPT. THE ACTUAL WX WAS APPROX 1200 FT OVCST AND 4 MI VISIBILITY. CAUTION SHOULD BE TAKEN WHEN USING AWOS RPTS. RECOGNIZE THEIR LIMITATIONS AND POSSIBILITY OF ERRORS.

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.