As I advanced the throttles on the mighty King Air, the airplane surged forward in a familiar manner. I was off on a trip to New Mexico with 4 people on board and the weather was beautiful, albeit hot. As I accelerated down the runway, I usually announce “airspeed alive”, but on this flight the airspeed did not come alive. I continued to accelerate down the runway and had to make a snap decision. Do I close the throttles and stop on the runway or continue the takeoff with no airspeed indication? I decided to continue the takeoff since the weather was VFR.
As I climbed the airspeed started to climb too, but it was clearly not accurate. I knew my power settings and performance parameters and quickly deduced that I had a pitot tube block. As I continued to climb the airspeed indication continued to climb. After about 5 minutes, I looked over at the copilot instruments and the airspeed was reading accurately (why it took me so long to look over there is still a mystery to me, and all I can attribute to this is “the fog of the situation”). I then decided to continue on my mission as I was making an intermediate stop only 50 miles into the trip.
During the whole trip to the intermediate stop, the airspeed indicator behaved exactly like a plugged pilot tube…meaning it behaved like an altimeter, increasing when I climbed and decreasing when I descended. I then began worrying about the reason behind the problem…did I forget to pull off the pilot tube covers? Was I to be completely embarrassed as I pulled into the busy FBO with a couple of red flags and smoking rubber on the front of the airplane? I turned off the pitot-heat just in case.
Upon landing I walked to the front and discovered that I had pulled the pitot tube covers and the pitot tube looked very normal. On the King Air, the pitot tube comes off fairly quickly with simple tools, and I had the pitot tube off in about 5 minutes. After getting it off, I tried to blow into the tube and sure enough…it was completely blocked. I took the tube into the FBO bathroom and tried to run some hot water through the pitot tube. With just a little bit of water a dozen or so dead spiders and a bunch of dirt flowed out. There was no doubt about it, a dirt dauber had made a home in my pitot tube.
Interestingly, I had the King Air inside a white-floor, very clean, completely enclosed hangar. And, it had been in this hangar for only 5 days since its previous flight, on which there were no pitot-problems. So, there was one very busy dirt-dauber working in my hangar!
We’ve instituted a policy of putting the covers on the various airplanes we manage at Casey Aviation, Inc even though they are in a super-nice hangar. The point…during the Spring/Summer/early Fall, dirt daubers and other flying insects can and will find small crevices and holes in which to build their houses. Make sure to use the covers and plugs for your airplane. My pitot-problem happened on a beautiful VFR day…yours might happen on an IMC day, and this could be far worse.