As I was trying to come up with a topic for this month’s article, I happened to read the “Waypoints” column in the June 2017 issue of AOPA Pilot magazine, written by Thomas B. Haines, the editor-in-chief. It tells of an incident in his 1972 Bonanza A36 in which he aborted a flight and taxied back to the avionics shop since the airspeed readouts – both on the Garmin G500, as well as on the backup display – were both reading a little less than 60 knots … and he surely wasn’t taxiing that fast! In fact, they kept reading that speed even when parked. It took the shop owner significant time to remedy the situation before Mr. Haines could depart. I think I could have saved them time and worry had I been there!
You see, I have seen this exact situation quite a few times in King Airs. It can happen when the airplane has sat outside in a windy rainstorm … as had happened to Mr. Haines before he tried to depart. The static ports on the aft fuselage – one or two per side, depending on your serial number – are connected by plastic tubing that then is routed up to the top of the fuselage from both side’s ports before moving forward in a single tube through the aft bulkhead and on to the static air instruments … airspeed, altimeter, and vertical speed. Here is what’s happening.
As the wind blows the rain against the static ports, some water enters the plastic tubing until the tubing fills with enough water to prevent the wind from having any further effect. As the wind abates and the pressure it applied to the side of the fuselage decreases, that little slug of water tries to drain out. However, the capillary action associated with the small tubing causes some of the water to remain in the tube. As the slug of water descends in the tube, it causes a decrease in the tube’s pressure upstream of the water. This erroneously low static pressure causes the airspeed indicator to show some speed, since static pressure is less than pitot tube, ram air pressure.
Had Mr. Haines not noticed the discrepancy – or decided to depart anyway – I am quite certain that the problem would have corrected itself as the vibration and airflow of flight would remove the rest of the water. I admire his decision not to depart, however, with this never-before-seen malfunction.
The shop cleared out the water by blowing high pressure air into the static port on one side while having a tissue to collect the water that was expelled from the opposite side. I presume the portion of the tubing going to the instruments from the junction of left and right ports was disconnected so that there’d be no chance of subjecting the static system to too much pressure.
Well, I have an easier, quicker way to solve this problem – kiss your King Air. Actually, you are not really kissing it, but I hope no one sees you doing this because it’ll surely look like you are! Merely put your lips and mouth up over the static port – you may need a stool on the King Air – and lightly suck. Be prepared for a little water to be ingested. Do it to both sides and then recheck your airspeed indicators in the cockpit. Fixed it, didn’t it? No access panels removed, no tubing disconnected, no shop air needed … just a little “kiss” and you’ll be good to go.
I bet that little tip was never covered in King Air ground school, was it?!