part, that with the complications and extra
cost of recertifying, I might as well buy a
new one. Of course, with light-sport aircraft or amateur-built airplanes registered
in the experimental category, that’s not the
case. I’m told many used autopilots wind
up in homebuilts.
If you’re flying a steam-gauge certified
airplane, the choices for a new autopilot
really come down to two companies,
Century or S-Tec. As is often the case, the
latter was formed when some employees of
the former moved across town to set up a
competing company—in this case, the town
is Mineral Wells, Texas. S-TEC is now a subsidiary of the UK company Cobham, and its
autopilots are among the most popular retrofit units for certified airplanes.
S-TEC autopilots are rate-based; that is,
they sense rate of turn through an electric
gyroscopic turn coordinator to make their
corrections. Century autopilots are attitude
(or “position”) based and take their informa-
tion from the attitude gyro. One advantage of
the S-TEC is that if the vacuum pump fails
and you lose gyro performance, the autopilot
can continue to fly the airplane while you
sort out the problem.
Newer aircraft almost all have electronic
flight information systems (EFIS), so called
“glass panels” that derive their data from
solid-state ADAHRS, rather than the gyros
and pitot-static systems in older aircraft.
ADAHRS data is far more precise, so those
aircraft have digital autopilot systems that
are more accurate than legacy analog systems. And the sensors in the ADAHRS units
are far more reliable than even the best
mechanical spinning gyros. These sensors
are the same type used to tell your iPad or
smartphone when it’s vertical or horizontal,
and they’re also used in automobile steering
and braking control systems.
So why don’t autopilot manufacturers
make modern digital autopilots?
Certification costs are the main culprit. The
FAA isn’t going to give the nod to a new system without extensive testing, and that costs
a lot of money.
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Find us at the following events:
March 27 - April 1, 2012
Booths #A-058 & #A-059
July 23 - 29, 2012
Booths #1073 & #1074