Gulfstream G550 Operating Manual Download

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by the SWPS function through the dual channels of the Flap Control Unit
(FCU). Position of each wing flap is reported by Rotary Variable
Displacement Transducers (RVDTs) to the respective FCU control channel.
Each of the FCU channels is connected over ARINC-429 links to the
MAUs. The SWPS software is programmed with a set of AOA values for
each flap setting, and triggers stall warning and prevention measures if the
values are exceeded.

To ensure that the AOA values used by the SWPS are the most accurate
possible, each MAU processor filters the input AOA data using time
averaging and compares inputs with the AOA data from the other MAU
processor and also with IRS pitch, roll, acceleration, change rates and True
Air Speed (TAS) a final refined AOA value.

Since the display of actual AOA would not be meaningful to the flight crew
due to the change in significance of the values with flap setting, the
software in the SWPS computes a normalized value for AOA. The
normalized value uses a format of zero (0) to one (1) with the indication
shown to two (2) decimal places, where 0.00 indicates zero lift on the wing
and 1.00 indicates the point of maximum wing lift. A normalized AOA value
of 1.00 is also the threshold of stick pusher activation, since any further
increase in AOA above the maximum lift angle results in a stall. The
normalized AOA value is displayed on the PFD below the airspeed tape.

B. Low Airspeed Indications:

The airspeed and AOA indications on the PFD provide the flight crew with
visual indications of deteriorating airspeed and high angles of attack. As
airspeed slows, the stick shaker threshold point is shown beside the
airspeed tape as a red bar descending with airspeed from the shaker
initiation point. If airspeed is slowing at a rate that will soon reach the
shaker initiation speed, the airspeed trend vector indicator will change to
amber. If airspeed reaches the stick shaker threshold, the digital airspeed
readout and AOA display will change to amber. Further airspeed loss that
initiates activation of the stick pusher is denoted by the digital airspeed and
AOA displays changing to red.

C. Yoke Stick Shakers:

Each cockpit yoke is equipped with an electrically powered stick shaker
installed under the flight deck floor. The motor for the pilot stick shaker is
powered by the left essential DC bus; the copilot shaker is powered by the
right main DC bus. The pilot yoke stick shaker is controlled by the SWPS
function in MAU #1 and the copilot stick shaker by MAU #2. The SWPS
software function activates the stick shakers at a threshold that provides
adequate margin for pilot action to avoid a stall. The stick shaker activation
point is set at:

•

A normalized AOA value of 0.90 for the first six (6) seconds after
takeoff (weight off wheels) to prevent nuisance activations

•

A normalized AOA value of 0.85 thereafter for all flap settings

These stick shaker thresholds provide at least a ten percent (10%)
airspeed margin prior to stick pusher activation and stall onset. Once the
stick shakers have been triggered, only a decrease in AOA below the
activation point will turn off the stick shakers. If a stick shaker malfunctions
and activates below the normalized AOA trigger threshold, the circuit

OPERATING MANUAL

PRODUCTION AIRCRAFT SYSTEMS

2A-27-00

Page 62
August 14/03

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