Page 16 - Volume 11 Number 11

Ask the Expert
Your Most Dangerous Flight
by Tom Clements
KAG II – the second King Air Gathering that was held at the Stevens Aviation facility in Dayton, Ohio (KDAY) on September 29-30, 2017 – was a great success with a full complement of King Air pilot attendees, sponsors, and presenters. (Editor’s Note: More details of KAG II on page 11.)
I was honored to be asked to be the kick-off speaker on Friday morning, a joyful task that I willingly accepted. The topic suggested to me was the one you see here: Your Most Dangerous Flight. I am sure our military King Air pilot brethren could provide numerous exciting examples of their own dangerous flights (that would be more dangerous than ours!), but for the average civilian pilot I am quite sure that the most dangerous flight is the first one that takes place after significant maintenance has been performed ... such as a phase inspection check, a propeller or engine overhaul, or a major avionics upgrade. I will give a recap of my KAG presentation here in this article. It will include numerous real-world examples of post-maintenance problems and suggestions about how to improve your odds of avoiding similar events.
I am sure most of you have seen the clever T-shirt that has the “33 Greatest Aviation Lies” stenciled on it. One that always brings a smile to my face is, “What could go wrong? It just came out of the Annual!” Replace “Annual” with “Phase Check” and it would fit King Airs perfectly. Here are some examples of surprises I have personally experienced or of which I have first-hand knowledge from stories told to me by my colleagues and customers.
Static Air Line Drains Left Open
LJ-542, a 1972 C90, was one my company owned and operated throughout the 1990s. Once I was picking it up by myself from a shop we often used after a routine phase inspection. It was a lovely clear morning; I did a thorough preflight inspection, both exterior and interior,
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and did all the run-up checks before I took off. I lifted off at about 100 KIAS, pitched up to my standard +10° attitude, retracted the landing gear, did a quick scan of the engine gauges, and then returned my scan to the flight instruments. What the ... ??? My airspeed was only 80 knots! I rechecked the torque gauges to ensure I was at takeoff power and rechecked my pitch attitude both visually and with the Attitude Indicator ... all normal. Knowing “Pitch plus Power equals Performance” I was sure the airspeed indicator was faulty. But – dang! – so was the one on the copilot’s side! By now they were decreasing below 60 knots. I reached over and moved the alternate air selector lever to the Alternate position. Nothing happened. I leveled off at 1,500 feet AGL pattern altitude, pulled power back to the middle “magic number” (500 ft-lbs for this C90), and stared in disbelief at the airspeed indicators that now were reading extremely high ... since they had decreased so much that the needles were beginning to point to the numbers to the left of zero!
Suspecting the problem, I reached down to the Pressurization Control switch and moved it to the Dump position. The cabin was only about 1,000 feet below the airplane with 0.5 psid differential pressure, so the dumping was not at all drastic. Immediately, the airspeed indicators resumed normal operation. I announced on the Unicom frequency that I was on left downwind for landing, proceeded with a normal landing, and taxied back to the shop’s ramp. I knew what was likely wrong and, sure enough, they found the static air line drains were all open. This allowed cabin air to enter the static system since the drains are behind an access panel low on the right sidewall of the cockpit, inside the pressure vessel. The entrance of cabin air, being at a greater pressure than ambient, was what led the airspeed indicators to read low, since they sensed less of a difference between pitot and static pressure. It absolutely blew my mind that a half of a psi error could lead to a negative airspeed indication!
NOVEMBER 2017