EAA Sport Aviation - February 2012

the past few years. I find that controllers are now routinely asking for pilot reports on clouds, but also on air temperature and any icing. The reports are being fed more efficiently into the system so other pilots are alerted, and forecasters can improve their outlooks. The old fear of “gotcha” for pilots flying unapproved airplanes into icing conditions is gone. I’m not saying there will never be another violation for flying an unapproved airplane into real “known” icing, but the controllers are clearly collecting and disseminating safety information, not looking to lock us up.

So don’t lock the hangar door just because there are cold clouds overhead. Just be sure to have an escape available if those rare conditions required to actually make airframe icing are there.

STATIC LEAK?

My airplane was due for its biennial altimeter and transponder checks. Any airplane that is flown IFR, or any airplane that has a Mode C transponder, has to have the altimeter/encoder accuracy, and transponder performance, checked by a certified shop every two years.

The altimeter check can be worrisome with mechanical altimeters and encoders because with age they can go out of tolerance. The aneroid that drives a mechanical altimeter can start to leak, or dirt can gum up the tiny precision gears that move the mechanism, and hysteresis can alter the behavior of springs and bellows. Often an instrument shop can overhaul an out-of-lim-its altimeter, but I have had to junk a couple over the years.

With new solid-state electronic encoders and air data computers the lack of accuracy is usually not an issue. The electronic components tend to work well until they fail entirely, rather than wandering out of calibration as a mechanical system can.

But a crucial part of the entire test is checking for leaks in the airplane static air source system. Even in unpressurized airplanes the air pressure inside the airplane is usually at least a little different than the air pressure outside the airplane that the static

What I am most encouraged
by is a new attitude shown
by controllers over the past
few years. I find that controllers
are now routinely asking for
pilot reports on clouds,
but also on air temperature
and any icing.

air system is detecting. A leak in the static
system means both the altimeter and the
airspeed can be inaccurate with no way of
knowing how inaccurate.

When the test equipment was hooked up to my pitot-static system it wouldn’t hold the lower air pressure applied to the test equipment. There was a small leak someplace. This could be a nightmare. The static plumbing connects to two ports on the aft fuselage, and then runs to a mechanical standby altimeter, two blind altitude encoders, an air data computer, and the autopilot computer. There are T-fittings and other couplings in addition to connections to the electronic components. And there are various types of tubing involved, some a rigid walled plastic, and other rubber-coated flexible lines. The leak could be anywhere.

But, lucky for me the guys at Mayday Avionics in Grand Rapids had been through this hundreds of times, and the first thing they checked was the alternate static source valve. I don’t know when the alternate static had been opened last—maybe during the annual inspection—but it was not sealing properly. Opening and then closing the valve caused it to seat and the leak was fixed. That was a close call on a lot of shop dollars spent trying to find a “real” leak. So be careful if you move the alternate static valve to make sure it closes tightly.

TOO OLD TO FLY?

The fact that the pilot flying a Cherokee 180
that crashed in Arkansas in November
killing two coaches of the Oklahoma State
women’s basketball team was 82 prompted
me to write a blog about how old is too old to
keep flying. There is no indication that the
pilot’s age had anything to do with the acci-
dent, which involved loss of control in good
VFR conditions, but the news media repeat-
edly called attention to the pilot’s age.

J. Mac McClellan, EAA 747337, has been a pilot for more than 40 years, holds an ATP certificate, and owns a Beechcraft Baron. To contact Mac, e-mail mac@eaa.org.