Now that most of the pilot population has become comfy and cozy with the AWOS (automated weather observation system) method of providing surface weather reports, it's time to break the news. AWOS is on its way out.
That's right, the nation's federally operated network of 160-plus AWOS units will be on borrowed time — beginning August 1. That's the day that the National Weather Service expects to commission the first five of a next- generation automated observation system. The first sites will be located at Alamosa, Colorado, as well as the Concordia, Dodge City, Goodland, and Topeka, Kansas, airports.
It's called the automated surface observation system, or ASOS. Though ASOS may sound confusingly similar to AWOS and, as such, appears to be just another dollop of Federal Aviation Administration jargon overkill, it's still very important for us to understand the new system. That's because ASOS is the wave of the future, a future in which all the foot soldiers in the NWS's observation network are machines. You see, like AWOS, the human observer is on the way out, too.
For those of us who might not be up to speed on AWOS, never used it, or never bothered to learn about it in the first place, a review is in order.
AWOS uses fully automated sensors to give pilots almost-real-time surface observations. These sensors feed a computer, which processes the information, updates it every minute, and broadcasts it. Pilots receive this information over a discreet frequency assigned to each AWOS unit; the frequency is published on charts, in the government's _Airport/Facility Directory,_ _AOPA's Aviation USA,_ and in various other aviation publications. You simply dial in the frequency and listen. A synthesized voice dishes out the details in a mechanical monotone. (N.B.: Some AWOS broadcasts are on frequencies spaced at .25kHz intervals, and will not be accessible to pilots equipped with standard 720-channel receivers). AWOS information can also be provided over the voice channels of certain VOR stations or through telephone or personal-computer contacts.
What you hear depends on the type of AWOS unit you've tuned in. AWOS I units report altimeter settings, wind speed and direction, temperature, dew point, and, in some cases, density altitude. AWOS II does all the above, in addition to reporting visibility. AWOS III is the top of the line, adding cloud ceiling information.
AWOS was — and still is — a great idea. It gives fairly reliable weather information (especially altimeter settings) at airports that ordinarily wouldn't be able to provide it. For many airports, AWOS meant the first-ever weather observations.
For other airports, AWOS meant lower descent minimums on already existing instrument approaches. At about $15,000 (AWOS I) to about $40,000 (AWOS III) a pop, AWOS isn't exactly cheap — but it makes so much economic sense that many state governments have established their own AWOSs, outside the federal program.
Furthermore, AWOS is on duty 24 hours a day, doesn't ask for raises, and can't go on strike. So if AWOS is so great, how come it's on the skids?
First of all, bear in mind that AWOS was intended from the start to be an interim system — an FAA program that would eventually be superseded by a joint Department of Transportation/FAA/NWS/Department of Defense effort. That's the squeaky-clean, official version of the AWOS/ASOS story.
Another aspect of the story involves dark hints about the questionable accuracy of AWOS reports and the AWOS units' less than perfect service history. Some in the weather bureaucracy claim that many AWOS ceilometers (the instruments that measure cloud height) are calibrated incorrectly. Others say that the automated sensor technology is too immature to provide the kind of accuracy pilots require. Still others point to the problems of single-source maintenance and complain that it can take weeks for a technician to repair a faulty AWOS. The AWOS contractor — Qualimetrics, of Sacramento, California — currently is responsible for servicing most of the AWOS units. Some say its repairmen are spread too thin.
The NWS says that it has learned from the AWOS experience and promises that ASOS will give more observations, higher quality observations, more information, and better quality control. Let's hope so if ASOS is the future. Bear in mind that ASOS reports will eventually replace human observations as the SAs of the future; as such, they'll be fed into the computer algorithms that will generate terminal forecasts and other predictive information.
Here are just a few of the reasons why the NWS says ASOS will be an exemplary product:
ASOS will provide everything that AWOS III now provides, plus present weather information; i.e., the type and intensity of rain, snow, or freezing rain. Certain significant remarks will also be broadcast such as variable cloud height, variable visibility, precipitation beginning and ending times, rapid pressure changes, pressure change tendency, and wind shifts. ASOS also reports precipitation accumulation in hundredths of an inch.
Class II ASOS units, which will serve at the nation's busier, controlled fields, will have three pressure sensors. This gives an almost surefire guarantee of full-time, accurate altimeter settings. Class I ASOS units, which are allocated to less active airports, will have dual redundant pressure sensors — just like today's AWOS units.
The NWS says that there will be one ASOS maintenance expert for every 15 units. The goal is to fix the units quickly. Failed ASOSs at major airports should be fixed within 12 hours. At smaller airports, repair times should be between 24 and 36 hours.
When the system is fully implemented in 1995, a total of 868 ASOS units will be in the field. According to the NWS, this will double the density of the weather observation network and therefore improve forecast reliability.
If automated systems — be they AWOS or ASOS — have the advantage of providing current (both units provide updated information every minute) observations, free of human subjectivity, they also have a big drawback. Critics of automated observations are quick to point out that human observers are still needed for at least one special skill — like spotting that thunderstorm 2 miles west and making a beeline for the airport.
You see, the laser-beam ceilometers used in AWOS III and ASOS shoot pencil-thin beams of light to do their jobs. These beams go straight up from the installation site and strike a very, very, very small piece of sky. A monster cumulonimbus cloud, full of lightning and tornadoes, could be right next to the beam, and the AWOS or ASOS would go right on reporting clear skies — until the unit is blown into the creek.
Officials in the ASOS program emphasize that no staff reductions are planned for the immediate future so that where ASOS units coexist with NWS observing sites, an observer will be on hand to personally add that all- important "T" (thunderstorm) notation to an ASOS report. At controlled fields, tower personnel will be assigned this special duty.
Sure, the NWS plans to add lightning detection systems to the automated observation system of the future, then merge their information with GOES satellite and Nexrad radar imagery to make up for the laser beam's shortcomings. But right now, these plans appear to be many months from implementation.
The AWOS program deals with ceilometer tunnel vision by offering AWOS IV, which provides all the AWOS III products, plus lightning detection, precipitation type and accumulation sensors, and a runway surface condition sensor. But so far, not one of these units has been ordered.
AWOS or ASOS, we'll be trading the convenience and operational flexibility of full-time weather reports for the odd chance of undetected severe weather — at least in the short term, until better storm detection is automated, too.
In the meantime, we'd better get used to the idea of automated observations. ASOS is right around the corner, and nothing is going to stop it. By the end of the year, 180 ASOSs are due to be installed; by 1993, some 557 will be in use.
Don't expect AWOS to disappear overnight. Just the opposite. AWOSs can last up to 10 years before they're kaput, so AWOS and ASOS will coexist for years to come. The FAA is budgeted to set up about 40 more brand-new AWOS units, which will make the federally supported AWOS network 200 strong.
Quite apart from this network are the AWOSs purchased and operated by state and local governments. The number of nonfederal AWOS installations is increasing at a rate of 30 percent a year. Minnesota and Tennessee lead the pack, with 42 and 31 installations, respectively. Seems the grass roots love AWOS, thank you.
Something to think about: In three years, there will be more than 1,300 automated observation sites at the nation's airports. Compared to today's human-based observation network, there will be hundreds more observation sites at hundreds more airports. In spite of automation's few shortcomings, pilots will realize an immense net gain in the quality, timeliness, and volume of weather reports. Whether you trust them or not, you'd better get used to the idea of listening to more machine-bred and -fed weather information. Let's just hope they don't phase out human observers so quickly that we're left with equipment still in its shakedown phase.
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