Just Plain Magic

Just Plain Magic

Just Plain Magic

The cloud detection system seen here works based upon reflections from lasers that point vertically and reflect the light back. The time it takes for the light to return, and how steady the return, determines the height and type of cloud layer.
A careful check of all wiring is completed by an FAA inspector during the inspection of an airport’s AWOS.

I am standing well away from the operations area of our airport in the middle of a huge meadow of tall yellow grass, with most of the green stalks having long ago given themselves over to the inevitability of fall. A shaft of sunlight is occasionally shining through the broken to overcast cloud layer about 2,000 feet above my head. And about 100 yards away a coyote is stalking a field mouse, occasionally giving me a worried glance to see if my presence might interfere with his activity. Circling above the coyote are a couple of noisy seagulls, wondering about possible leftovers from the coyote. 

Out in the distance, and far away from the wildlife, I can hear a single-engine piston-powered airplane starting on its takeoff run. Shortly after that, it passes through my line of sight just some 20 feet above the runway. I strongly suspect that the pilot, if he can see me at all, has no idea the importance of the aviation equipment I am out here looking at. Until several years ago, I would not have known myself. But what I and three others are doing out in the middle of this mouse habitat, is checking the accuracy of our airport’s AWOS (automatic weather observation system) – the magic of which we pilots are often oblivious to (until it doesn’t work), even though it has made a huge difference to the safety and efficiency of how we fly. 

A good example is a flight I was on about 10 years ago, where we wanted to depart the Chicago area for our home airport (BVS) in western Washington. It was nighttime and the weather in Chicago was not too bad, however, an occluded front was moving through our destination. Weather at all of the local airports was frequently going below IFR approach minimums. Company policy (quite reasonably) required that we know the weather of our arrival airport before filing the flight plan. So, using the old fashion call-in system to the FAA’s contracted weather briefer, we made the inquiry only to be told the current weather at our chosen destination was not available. The employees of the airport who provide the weather had already gone home for the day. We had two choices – delay the flight until the weather was available in the morning, or file to a different airport some 50 miles away, which did have weather available until midnight. A big problem was all of our cars were at our planned destination. So, rather than get stuck somewhere 50 miles from home looking for a late-night pickup from an overbooked motel, we chose to spend the night in Chicago. 

Was that an expensive inconvenience to our passengers who had business to conduct the next day? You bet. And all because we simply did not know the weather of the arrival airport. When we got home, I began to study the effect this lack of information was having on the operations and economics of our airport. It turned out what we had experienced was a regular event during the winter months, when nights are long and weather poor. The cost to the airplane operators from all the displaced or delayed flights was enormous, and it also affected the reputation of our airport as a well-equipped and business-friendly place to fly.

As it happened, there was a technology evolution going on at the time to resolve the problem. Various companies had designed equipment that would automatically measure ceiling elevation and type, altimeter settings, wind direction and speed, temperature, dew point and visibility. It then automatically put it on the national aviation weather reporting system, or convert it to an electronic human voice and transmit the information over a discrete (AWOS) frequency. Within a year our airport had the equipment installed, with all its funny looking antennae out in the meadow, where it did not in the least disturb the lives of the coyotes and mice.  

Just two weeks ago, I was returning again from the Midwest, leaving after our passengers completed their business and ate a late dinner. There was a moist onshore flow over the Pacific Northwest, with temperature and dew points gradually closing and fog predicted as the night wore on. From our cell phones no less, we dialed up the weather at KBVS on ForeFlight, found the AWOS reported visibility to be 3 miles and ceiling 1,500 feet, but with the temperature and dew point closing. With that information in hand we were legal enough to depart by company policy but were nevertheless concerned that by the time we arrive 3 hours later, the dreaded fog might make the area below minimums. As we headed west at FL450, however, the AWOS continued to provide real-time weather information via text on our iPads. Finally, at 11 o’clock at night, within 100 miles or so of our destination, we tuned in the discrete AWOS frequency and heard an entirely artificial but calm and assuring male voice state that the visibility was now 2 miles, winds calm, ceiling 800 and temp/dew point within 2 degrees of each other – all well within our minimums for the GPS approach we intended to make. As we pulled the power back and started down, I could not help but think about the magic of it all, and how much safer flying had become over the past decade with the kind of weather reporting now available 24/7 from most airports. 

In reflecting about the trip, I started wondering about how exactly the system works so reliably year-round, without a need for days off, and what was required to make sure it was maintained and working accurately. And that is what led me to stand in the middle of the meadow, glancing between the coyote and one of the technicians 30 feet up on the antenna. How the system works and is maintained is both ingenious and simple.

The cloud detection system works based upon reflections from lasers in a metal box that point vertically and reflect the light back. The time it takes for the light to return, and how steady the return, determines the height and type of cloud layer. But then you wonder what happens when one of those seagulls fly directly over on a bombing run and hit the glass covering the laser. When this happens, the sudden decrease in light turns on a fan, which blows a strong blast of air across the glass and removes the bird’s donations. The FAA requires that this mechanism is checked annually to ensure the automatic bird poop blasting fan is actually working. Fortunately for us, the test does not require handling bird droppings. To test for it, all we had to do was tape some white paper across the glass then watch to see how the machine reacted. Sure enough, the machine decided the seagulls visited and the fan came blasting on. The next test was to see if it would turn itself off once its bird poop cleaning job was done. So we removed our taped paper and again waited to see what would happen. After considering it for a while, the machine shut the fan off. Test completed and carefully documented by the present FAA inspector.

The device to test AWOS temperature and dew point was a surprisingly simple handheld instrument, comprised of two mercury thermometers mounted side by side in a small tray which you could spin by hand. One of the thermometers had a small cotton sock over the mercury end while the other was uncovered. The test involved soaking the sock with some bottled drinking water we brought with us, then spinning the device until the sock dried off. This boring task was naturally assigned to the most junior of the testing crew, namely myself. After spinning the thing out in the middle of the pasture for what seemed like an eternity, the two thermometers were carefully inspected with the wet one being about 3 degrees lower than the dry one. This, of course, occurred because the evaporation of the water on the sock cooled that thermometer more than the adjacent one. This high-tech data was then compared to what the AWOS was showing and matched almost dead on. This also was dutifully recorded by the FAA inspector.

Our next test was to measure the accuracy of the wind speed impellor and vane at the top of the tower. For this test, our more athletic member climbed the tower, removed the impellors from the wind speed measurer, and connected it to a battery-driven drill motor that ran at a very specific speed. Providing the computer on the AWOS showed a wind speed that matched the known number for that RPM, that test also passed. 

The wind vane was much simpler. It only needed to be determined if it rotated freely and if its direction was accurate. We determined direction by hauling out our cell phones, going to the APP that shows compass direction, then making sure what the vane was pointing at reflected the number on our phones. A careful inspection of all the wiring followed, and it was noted there was some corrosion on the endpoint of one of the co-ax cables. The FAA inspector looked at this closely and said it would need to be replaced, but the system would remain approved until this was done. 

During our testing, several airplanes arrived whose pilots had no doubt checked the airport’s weather before taking off. And based upon what this equipment in the middle of a field was showing, filed the flight from halfway across the country.; the pilots oblivious to the magic of it all. 

Next time you see a small antenna farm out in the middle of the grass somewhere on your airport, don’t just wonder why some bureaucratic dingbat allowed those obstacles to be installed there. They serve a purpose that benefits us all, and we often take the system for granted, and the people that maintain them. From anywhere in the world, we can know exactly what the weather is at our home airport just by looking at our cell phone. Times have indeed changed from a decade ago, and what we have now is, by comparison, just plain magic.  

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