At right, the turn coordinator
depicted at top displays a slip: The airplane is in a standard-rate turn to the right and the inclinometer's ball is positioned well out of its cage, to the inside of the turn.
Electrical failure could kill the turn coordinator
, autopilot and, most importantly, the com radios and GPS navigator.
The entry-level models include the System Twenty and Thirty, as well as the ATI panel-mounted System Forty, which uses a separate turn coordinator
Mid Continent's 1394T100-7Z is a common, electric turn coordinator
and costs around $600 to overhaul.
Rate-based autopilots, though generally considered less smooth and capable than their more-expensive cousins, present a decided advantage: They will continue flying the airplane as long as the turn coordinator
driving them works.
If you're down to the turn coordinator
for roll control, it's not much harder.
The System 30, as with nearly all S-TEC autopilots for light aircraft, is rate-based with an electric turn coordinator
commanding near-standard-rate roll input.
A short list of possibilities includes electrical failure, attitude indicator failure, heading indicator failure, turn coordinator
failure, accidentally or inadvertently touching the trim switch (in some models, bumping one side of a split trim switch will disconnect the autopilot but leave a flight director engaged, making it look like the autopilot is still doing all the work), trim servo failure, GPS or VOR/localizer system failure, antenna connection corrosion, pilot activation of the wrong autopilot or nav system mode, airframe ice accumulation (that impedes trim or control surface movement), turbulence, a right-seat passenger's nudge on the control yoke or curious push of a button .
Then I watched an old ARC autopilot fly a perfect ILS, using only the CDI needle and the turn coordinator
As a general rule, autopilots that are rate-based--using a turn coordinator
gyro for a primary reference--are less expensive to maintain given their simplicity.
Great article on the turn coordinator
, which sometimes seems to be a neglected corner of the instrument panel these days.
On the panel: The mags are off, the fuel is off, ALT and VAC have been switched on the gauge, the turn coordinator
is AC powered, the KTAS index is numbered backwards, the whiskey compass is numbered backwards, the altimeter shows 91,700 feet, the Kollsman window numbers are too high, the squawk code includes an eight and the view out the window shows mountains even though the aircraft is heading out to sea.