STEC System 30 Autopilot
Gene Robinson & Hank Eilts
July 9, 2005
The STEC System 30 POH Supplement in the aircraft is the supreme authority about how to use and
control the autopilot. If any information contained herein is contrary to the POHS, the POHS rules.
• Autopilot Benefits
– Reduced workload
– Less pilot fatigue
– Increased flying enjoyment
• Maintains Altitude and Heading
– A virtual copilot.
– Permits chart reading, radio tuning, ATC communications, etc.
without risk of a deviation.
• Navigation: An autopilot can help by
– Holding a heading
– Tracking a VOR, GPS, or LOC radial or course
• Fly the aircraft onto the course, then
• Engage the desired autopilot mode.
• At a waypoint or station passage, use the heading mode or disconnect
the autopilot to prevent large course excursions.
– Approaches are both simpler and more precise with the autopilot.
• Fly the aircraft onto the approach course prior to engaging the autopilot.
• The pilot retains command by choosing how much of the flight to
hand fly and when to use the autopilot while tending to other
• With an autopilot to reduce workload on long cross-country flights
pilots will tend to be more relaxed, more comfortable, and safer
• Don’t Forget to Always Fly the Airplane!
– Do Not to Forget to DISENGAGE THE AUTOPILOT TO FLY THE
– MANUALLY FLY THE AIRPLANE TO MAINTAIN YOUR FLIGHT
PROFFICENCY AND TO
– MAINTAIN YOUR INSTRUMENT SCAN PROFFICENCY FOR
APPROACHES AND LANDINGS
System 30 Autopilot
Horizontal (Roll Axis) Modes
– Stabilizer Mode
– A “wing leveler”
– Direction info from the
DG and heading bug
• 2 NAV Track Modes
– Track the CDI signal
– LO TRK
• Low gain tracking
• Recommended VOR
– TRK HI
• High gain tracking
• Use for GPS tracking
and all approaches.
Horizontal Modes (continued)
Pushing (momentarily) the Mode lights
mode button cycles through illuminate to
the horizontal modes. indicate the
One push advances to the mode in use.
Holding the mode button
down disconnects the
The green ready light Red Flag
indicates that the autopilot 1. Voltage < 9 volts
is on and ready, but not
2. RPM < 20%
Lo Gain and Hi Gain Track
• Use for VOR enroute (LO TRK) and GPS & Approaches (HI TRK)
– STEC 30 can track VOR & LOC on approaches
– STEC 30 won’t track a backcourse approach
– Use the nav coupling switch (lower left panel) to couple the desired
nav receiver to the autopilot.
• Tracks the CDI signals from the Nav Receivers.
• POH Directive: Prior to engaging the autopilot in a TRK mode,
position the aircraft within 1 CDI needle width of the radial or GPS
desired track and within 10o heading.
– If you don’t do this, you can make the autopilot fly in circles (literally).
• In general, the autopilot won’t track well across station passage or
GPS waypoint passages.
– The STEC 30 autopilot does not anticipate turns.
– Options: hand fly the passage or use autopilot/heading bug.
Vertical (Pitch Axis) Mode – Altitude Hold
You must have a horizontal mode engaged in order to engage altitude hold.
Altitude hold light indicates that
altitude hold is engaged.
Altitude hold is engaged and
disengaged by pushing the
altitude hold button.
Trim annunciators ask the pilot for nose
up or nose down trim, respectively, and
give an audio alert (beeps).
Altitude Hold Techniques
• The professional way to engage altitude hold is to hand fly the airplane
to near level at your target altitude, then engage altitude hold.
• The lazy way is to climb/descend to altitude, engage altitude hold, and
let the autopilot capture the altitude. The trim annunicators will yell at
you, followed by your passengers (“What’s that?”) or your instructor
(“That’s a poor procedure!”), but the autopilot will capture the altitude
(perhaps with overshoots and undershoots)
• Some turbulence may set up a scenario where the autopilot pitch control
can aggravate the physical discomfort of the turbulence. Remember,
passengers generally don’t have as much physical immunity to bumps
and turbulence as pilots – Nausea can be a concern.
• The autopilot controls pitch up to a maximum of +/- 0.6G. That is, the
autopilot can command the aircraft to pitch up/down between 0.4G and
• Also, remember the requirement to set the altimeter at least every 100
miles (FAR 91.121). The altitude hold autopilot tracks a constant
pressure altitude. So, “High to low, look out below” still applies.
– Periodically reset your altimeter, disable altitude hold, readjust the aircraft’s
altitude, then re-enable altitude hold.
• The autopilot will function normally in light to moderate turbulence –
the kind that is annoying to pilots and nauseating to passengers.
– The vertical mode trim annunciators may yell at you, but the autopilot
will function without problem. Disengaging altitude hold may make the
ride smoother (maybe not).
• For turbulence levels greater than this, the horizontal modes can
help you, but the altitude hold can hurt you.
– The horizontal modes can help hold the wings level and help you hold
your heading. The pilot may want to “assist” the autopilot, but that’s OK.
– Altitude hold should be disengaged.
• REMEMBER: proper piloting in turbulence is to slow below maneuver speed
and hold attitude, not altitude. The altitude hold autopilot doesn’t do this .
• In response to an updraft, the autopilot may pitch down and cause the
aircraft to exceed maneuver speed.
• In response to a downdraft, the autopilot may pitch up and cause the aircraft
to get too slow.
Coping with Common Problems & Emergencies
• Vacuum Failure: Kills your directional gyro
– Autopilot impact: None, except for heading bug tracking
– Solution: Don’t couple autopilot to the heading bug.
• Alternator Failure: Kills the autopilot after a short time.
– After battery discharge to 9 volts or so, red flag will display on the turn
coordinator/autopilot, and autopilot will automatically disengage.
– Solution: Hand fly the airplane.
• Static System Ice: Makes the altitude hold mode unreliable.
– Solution: Disengage altitude hold mode. Engage pitot heat (the arrow’s
static ports are on the pitot tube).
• Autopilot Failure or Erratic Behavior
– Don’t try to diagnose an autopilot problem in the air.
– Solution: Disengage & power off the autopilot. Hand fly the airplane.
– By design, the pilot can always physically override the servos.
• Sooner or later, everything mechanical in the airplane can and will
fail. Count on it happening, because it will.
• Always have a reasonable “Plan B” for every contingency. The pilot
and his proficiency are “Plan B” for an autopilot failure.
• The autopilot should have flight importance similar to a cruise
control on an automobile.
– If it fails, no big deal. I can always hand fly the airplane.
• Don’t extend your personal limits beyond your comfort zone just
because we now have an autopilot.
• Don’t ignore your instrument scan while on autopilot.
• Don’t fly continuously on the autopilot. Take time to practice hand
flying the airplane. Don’t let your skills deteriorate by relying on a
– Let the autopilot’s performance challenge you. Can you hand fly the
airplane as well as the autopilot? If not, practice, practice, practice.