Narrative:

I am an air traffic controller at peoria, il, and I've worked with ASOS for over 8 months now. ASOS is what gives you WX information instead of human observers at many airports. As far as measuring cloud hts, ASOS has a very accurate ceilometer. It falls short in trying to determine different types of layers. Very often it classifies a scattered layer as broken or vice versa. It is a mystery how it comes up with the remark 'scattered variable broken,' but it does so regularly. When that layer is 3000 ft or less, ASOS generates a lot of special observations, which results in us spending a lot of time recording ATIS messages instead of separating airplanes. Often it will miss a cloud layer entirely if it is not directly above the sensor. This should not be a problem as human observers are contracted to augment the ASOS WX reports. However, the contractor seem unwilling to change anything ASOS puts out, probably because of their desire to avoid paperwork. Visibility seems to be a real problem area. The reported visibility is pretty accurate when the WX is nice, but when visibility is marginal, ASOS is apt to be incorrect a significant part of the time. I can recall an instance when it reported the visibility below minimums (when we could see farther than the tower), forcing a commuter aircraft carrying passenger to circle in freezing conditions. I realize the visibility from the tower might differ from the visibility on the surface (and we do our best to forward correct information to the contractor), but discrepancies seem to happen more often than they should. Another problem comes up when there is a thunderstorm. ASOS cannot determine its location and movement, and the contractor seems unwilling to include this information in the WX report. This information seems to be very important to many pilots as they often ask about it. When it comes to wind information, ASOS might have the edge over equipment we have in the tower. Our equipment retains gust information for just 2 mins. I don't know how long ASOS retains gust information, but the standard is 10 mins. The equipment ASOS uses to measure altimeter setting seems very accurate. However, the remarks 'pressure rising rapidly' or 'pressure falling rapidly' appear with alarming regularity when there is little, if any, movement in barometric pressure. Now, as a taxpayer, I applaud any effort on the part of the federal government to save money. But as a member of the flying public, I don't think we should be applying a cost/benefit ratio to safety. Maybe the FAA should be using ASOS to augment human observers instead of using human observers to augment ASOS.

Google
 

Original NASA ASRS Text

Title: CTLR ALLEGES THE ASOS HAS A PROB DETERMINING DIFFERENT TYPES OF CLOUD LAYERS, OFTEN REVERSING THE SCATTERED AND BROKEN LAYERS. VISIBILITY RPTING IS PRETTY ACCURATE EXCEPT WHEN VISIBILITY IS MARGINAL. ASOS CANNOT DETERMINE LOCATION AND MOVEMENT OF A TSTM.

Narrative: I AM AN AIR TFC CTLR AT PEORIA, IL, AND I'VE WORKED WITH ASOS FOR OVER 8 MONTHS NOW. ASOS IS WHAT GIVES YOU WX INFO INSTEAD OF HUMAN OBSERVERS AT MANY ARPTS. AS FAR AS MEASURING CLOUD HTS, ASOS HAS A VERY ACCURATE CEILOMETER. IT FALLS SHORT IN TRYING TO DETERMINE DIFFERENT TYPES OF LAYERS. VERY OFTEN IT CLASSIFIES A SCATTERED LAYER AS BROKEN OR VICE VERSA. IT IS A MYSTERY HOW IT COMES UP WITH THE REMARK 'SCATTERED VARIABLE BROKEN,' BUT IT DOES SO REGULARLY. WHEN THAT LAYER IS 3000 FT OR LESS, ASOS GENERATES A LOT OF SPECIAL OBSERVATIONS, WHICH RESULTS IN US SPENDING A LOT OF TIME RECORDING ATIS MESSAGES INSTEAD OF SEPARATING AIRPLANES. OFTEN IT WILL MISS A CLOUD LAYER ENTIRELY IF IT IS NOT DIRECTLY ABOVE THE SENSOR. THIS SHOULD NOT BE A PROB AS HUMAN OBSERVERS ARE CONTRACTED TO AUGMENT THE ASOS WX RPTS. HOWEVER, THE CONTRACTOR SEEM UNWILLING TO CHANGE ANYTHING ASOS PUTS OUT, PROBABLY BECAUSE OF THEIR DESIRE TO AVOID PAPERWORK. VISIBILITY SEEMS TO BE A REAL PROB AREA. THE RPTED VISIBILITY IS PRETTY ACCURATE WHEN THE WX IS NICE, BUT WHEN VISIBILITY IS MARGINAL, ASOS IS APT TO BE INCORRECT A SIGNIFICANT PART OF THE TIME. I CAN RECALL AN INSTANCE WHEN IT RPTED THE VISIBILITY BELOW MINIMUMS (WHEN WE COULD SEE FARTHER THAN THE TWR), FORCING A COMMUTER ACFT CARRYING PAX TO CIRCLE IN FREEZING CONDITIONS. I REALIZE THE VISIBILITY FROM THE TWR MIGHT DIFFER FROM THE VISIBILITY ON THE SURFACE (AND WE DO OUR BEST TO FORWARD CORRECT INFO TO THE CONTRACTOR), BUT DISCREPANCIES SEEM TO HAPPEN MORE OFTEN THAN THEY SHOULD. ANOTHER PROB COMES UP WHEN THERE IS A TSTM. ASOS CANNOT DETERMINE ITS LOCATION AND MOVEMENT, AND THE CONTRACTOR SEEMS UNWILLING TO INCLUDE THIS INFO IN THE WX RPT. THIS INFO SEEMS TO BE VERY IMPORTANT TO MANY PLTS AS THEY OFTEN ASK ABOUT IT. WHEN IT COMES TO WIND INFO, ASOS MIGHT HAVE THE EDGE OVER EQUIP WE HAVE IN THE TWR. OUR EQUIP RETAINS GUST INFO FOR JUST 2 MINS. I DON'T KNOW HOW LONG ASOS RETAINS GUST INFO, BUT THE STANDARD IS 10 MINS. THE EQUIP ASOS USES TO MEASURE ALTIMETER SETTING SEEMS VERY ACCURATE. HOWEVER, THE REMARKS 'PRESSURE RISING RAPIDLY' OR 'PRESSURE FALLING RAPIDLY' APPEAR WITH ALARMING REGULARITY WHEN THERE IS LITTLE, IF ANY, MOVEMENT IN BAROMETRIC PRESSURE. NOW, AS A TAXPAYER, I APPLAUD ANY EFFORT ON THE PART OF THE FEDERAL GOV TO SAVE MONEY. BUT AS A MEMBER OF THE FLYING PUBLIC, I DON'T THINK WE SHOULD BE APPLYING A COST/BENEFIT RATIO TO SAFETY. MAYBE THE FAA SHOULD BE USING ASOS TO AUGMENT HUMAN OBSERVERS INSTEAD OF USING HUMAN OBSERVERS TO AUGMENT ASOS.

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.