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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 Aeromania 32 • TWIN & TURBINE / October 2019 Jet Journal