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					                        Arrow N7508J
                    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
                             INCREASED SAFETY
   – 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
   – Approaches are both simpler and more precise with the autopilot.
       • Fly the aircraft onto the approach course prior to engaging the autopilot.
                      Intro Summary

• The pilot retains command by choosing how much of the flight to
  hand fly and when to use the autopilot while tending to other
  important duties.

• 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!
System 30 Autopilot


                   Lower Left
                Instrument Panel
         Horizontal (Roll Axis) Modes

• ST
   – 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.
 next mode.
 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%
                         Horizontal Modes
                       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.
                Turbulence Techniques
• 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.
                             Pilot Attitudes
•   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.

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