AEA Pilot's Guide 2020-2021 - 65

The pilot of the household paused, momentarily
stumped because he considered autopilots as one of
those signs that an aviator has "arrived," if you will.
Then the nonflying spouse let the pilot spouse off
the hook.
While the flying spouse stumbled to form an answer,
the nonflying spouse tossed a well-known aviation
magazine on the lap of the flying spouse.
"Why didn't you tell me about the safety benefits
of an autopilot, and why didn't you say you need help
sometimes?" she asked.
The two previously flew together for nearly 2,000
hours, and all those hours flew without an automatic flight
control system installed and operating in their complex
piston single.
The nonflying spouse regularly held the yoke as the
flying spouse took pen in hand after the controller chimed
in with the dreaded phrase, "November somethingsomething, stand by to copy an amended clearance."
The nonflying spouse then commented on the rough
air to ask how the flying spouse handled such situations
when flying alone, which was most of the time.
"Very carefully," the flying spouse responded, "very
carefully."
You can probably guess how this discussion
concluded: With the pilot spouse diving into research to
identify the best flight control-system solution for their bird
and their budget.
"We can get it installed at annual," the nonflying
spouse offered, "and we'll have it to help when we fly
home for the holidays."
What pilot would possibly decline that offer?
That was years ago when the dominant single-axis
systems worked well tracking a heading or following a
VOR signal. Two-axis models added altitude hold, while
other so-called wing levelers did only what the name
implies: Hold a wings-level attitude independent of any
navigation input.
Such systems remain on the market, joined in recent
years by flight control systems far more capable and
sophisticated than anything short of a business-turbine
panel - back then.
Today, the choices available would have seemed
far-fetched for light piston aircraft - flight control systems

capable of all the above functions, plus following a GPS
course, following the flight plan in a GPS navigator, even
navigating complex instrument approaches, including
descents to decision height on short final.
These functions once stood as the exclusive purview
of highly sophisticated flight-management systems used
in turbine-powered aircraft, from light general aviation up
through and including business jets and airliners.
Best of all, many of these systems are available for far
less than our turbine-flying friends' systems, with many
within reach of owners of even the most modest aircraft.
And the selections are significant.
Some basics
For decades, the dominant autopilot sensing technology
for light GA aircraft used a rate-based system driven by
the electric turn coordinator to sense attitude changes.
Prior to those systems, pneumatic-driven systems used
air pressure to move the appropriate control surface in the
correct direction.
The other sensing technology employed in autopilots
is the attitude-based system, which senses roll and pitch
changes from the attitude indicator.
The rate-based approach enjoys some advantages and
disadvantages, like most any aircraft system.
On the safety side, electric turn coordinator rate
gyro works independently of the attitude gyro, which
predominantly gets power from the aircraft vacuum system
used to drive the attitude gyro.
For the attitude-based system, the failure of either
the attitude gyro itself or the vacuum pump powering
the attitude indicator spells the loss of the flight control
function. With the same failure - an attitude indicator
failure of whatever cause - the turn coordinator and the
rate-based autopilot suffer no ill effects.
The rate-based autopilot continues to drive the flight
control system unaffected by the failure of the attitude
indicator or air pump.
Additionally, rate gyros won't tumble due to flight in
unusual attitudes. That's why flight instructors teach
their students to recover from unusual attitudes or loss
of control using the turn gyro - either the turn and bank
Continued on following page...

- 65 -

AEA Pilot's Guide 2020-2021

Table of Contents for the Digital Edition of AEA Pilot's Guide 2020-2021