Section 7 - System Description; Afcs Overview - Piper CHEROKEE ARCHER II Pilot Operating Handbook

AFCS OVERVIEW

The GFC 500 is a digital Automatic Flight Control System (AFCS). It is a two-axis autopilot and flight director
system which provides the pilot with the following features:
G5 Outputs to Autopilot — The G5 flight instrument provides attitude, rate, and acceleration information to the
servos. Additionally, indicated airspeed, vertical speed, pressure altitude and GPS information are sent to the
autopilot for mode control.
Flight Director (FD) — The flight director processing occurs in the G5 instrument. Selected modes for the flight
director are displayed on the G5 autopilot status box.
The flight director provides:

Command Bars showing pitch/roll guidance

Vertical / lateral mode selection and processing
Autopilot (AP) — Autopilot operation occurs within the pitch, roll, and optional pitch trim servo. It also provides
servo monitoring, and automatic flight control in response to flight director steering commands, attitude and rate
information, and airspeed.
Optional Electric Pitch Trim — The pitch trim servo provides manual electric pitch trim capability when the
autopilot is not engaged. The trim servo provides automatic pitch trim when the autopilot is engaged and the
airplane is in the air. Automatic trim functionality is disabled on the ground.
GMC 507 — Pilot commands to the autopilot and flight director are entered through the GMC 507 autopilot mode
panel. The GMC 507 contains internal sensors which calculate the aircraft attitude, attitude rate and
accelerations. These inertial sensors are completely independent from the sensors within the G5 and the rest of
the autopilot system, and are not used for the flight director, autopilot, trim or ESP functions. They are used
solely to provide independent monitoring of the GFC 500.
Airspeed and Altitude Information — The GFC 500 requires airspeed and altitude information from the G5
instrument.
Other components of the AFCS include the GSA 28 pitch, roll, and optional pitch trim servo that also contain
autopilot processors, control wheel mounted elevator trim switch (if trim servo is installed), control wheel mounted
autopilot disconnect and trim interrupt button (AP DISC / TRIM INT), and a Go-Around (GA) button.
Underspeed Protection (USP) — The GFC 500 will provide Underspeed Protection when the autopilot is
engaged.
When the minimum airspeed of 65 KIAS (75 MPH) is reached, a visual MINSPD message will appear above the
airspeed tape and the autopilot will lower the nose to maintain 65 KIAS (75 MPH). An aural "AIRSPEED,
AIRSPEED" voice alert will sound for installations connected to an audio panel.
Underspeed Protection is inhibited when the airspeed exceeds 70 KIAS (80 MPH).
Overspeed Protection (OSP) — The GFC 500 will provide Overspeed Protection when the autopilot is engaged.
When the maximum airspeed of 140 KIAS (160 MPH) is reached, visual MAXSPD message will appear above the
airspeed tape and the autopilot will raise the nose of the aircraft to avoid exceeding 140 KIAS (160 MPH). An
aural "AIRSPEED, AIRSPEED" voice alert will sound for installations connected to an audio panel.
Overspeed Protection is inhibited when the airspeed is below 135 KIAS (155 MPH).
Coupled Go-Around — Pressing the GA button will not disengage the autopilot. Instead, the autopilot will
attempt to capture and track the flight director command bars. If insufficient airplane performance is available to
follow the commands, the autopilot will enter Underspeed Protection mode at the minimum airspeed.
Electronic Stability and Protection (ESP) — The GFC 500 will provide Electronic Stability and Protection when
the autopilot is not engaged.
190-02291-07 Rev. 4
SECTION 7 – SYSTEM DESCRIPTION
AFMS – GFC 500 Autopilot in Piper PA-28 Series
Page 7–1