Aero-Tips!
A good pilot is always learning -- how many times have you heard
this old standard throughout your flying career? There is no truer
statement in all of flying (well, with the possible exception of
"there are no old, bold pilots.") It's part of what makes aviation
so exciting for all of us... just when you think you've seen it
all, along comes a scenario you've never imagined.
Aero-News has called upon the expertise of Thomas P. Turner,
master CFI and all-around-good-guy, to bring our readers -- and us
-- daily tips to improve our skills as aviators, and as
representatives of the flying community. Some of them, you may have
heard before... but for each of us, there will also be something we
might never have considered before, or something that didn't
"stick" the way it should have the first time we memorized it for
the practical test.
It is our unabashed goal that "Aero-Tips" will help our readers
become better, safer pilots -- as well as introducing our
ground-bound readers to the concepts and principles that keep those
strange aluminum-and-composite contraptions in the air... and allow
them to soar magnificently through it.
Look for our daily Aero-Tips segments, coming each day to you
through the Aero-News Network. Suggestions for future Aero-Tips are
always welcome, as are additions or discussion of each day's tips.
Remember... when it comes to being good pilots, we're all in this
together.
Aero-Tips 03.01.06
The FAA has issued Special Airworthiness Information Bulletin
(SAIB) SW-06-21 concerning "certain autopilot components that could
exhibit a potential failure of the Turn Coordinator causing the
[autopilot's] roll computer to drive the servo when not
commanded..."
NOTE:
- Turn coordinator-referencing autopilots include those built by
S-TEC.
- The KAP 140 autopilot, very common and installed in
current-production Cessna and Diamond airplanes, also references
the turn coordinator.
- Older autopilots may also use a turn coordinator source.
- "Glass cockpit" airplanes with these autopilots use a hidden
turn coordinator-like gyroscope that may suffer the same failure
modes.
Check the Pilot's Operating Handbook autopilot supplement for
the airplane you fly.
SAIB SW-06-21 warns that a failed turn coordinator or something
as simple as a loose grounding strap from the turn coordinator's
power supply can cause the autopilot command a roll.
This has ramifications also for flight if the turn
coordinator becomes inoperative or its circuit breaker pop.
The warning continues: "When this failure occurs the
autopilot might (if equipped) display... an "AP Ready" annunciation
even though the roll axis is in a failed or misleading
condition. This failure may result in loss of control of the
aircraft."
The FAA has "field data to support that when the Rate Gyro of
the Turn Coordinator losses [sic] its power reference signal, the
Roll Flight Guidance Computer would continuously drive the servo in
a non-commanded direction. The field data...identifies that
this failure may occur in various autopilots."
The SAIB lists three recommendations, condensed here:
- Perform a preflight test to check all modes of the
autopilot as contained in the Pilots Operating Handbook autopilot
supplement.
- Disconnect the autopilot and hand-fly the airplane if you see
any deviation from expected flight path.
- Check the turn coordinator power reference for proper grounding
during annual inspection.
I’d add carefully observing proper turn coordinator
operation during taxi, and active instrument cross-check in
flight.
Aero-Tip of the day: Know how your
autopilot works, how to test it, and its failure modes. Never
let an autopilot take you anywhere you can’t immediately take
over and hand-fly.