More stuff on the system
VI. STALL PROTECTION SYSTEM
A. General Description
The Stall Protection System (SPS) provides indications when the aircraft is nearing a
stall condition, provides indications when the aircraft is actually in a stall condition,
and provides positive inputs to assist the crew in eliminating the stall condition. The
SPS has two primary functions, they are:
• Stick Shaker
• Stick Pusher
The SPS uses stick shakers to provide tactile and aural warnings to alert the crew of
an impending stall. Also it uses a stick pusher to assist the crew in eliminating a stall
by moving the elevators to reduce the angle of attack (i.e. pushing control columns
forward). Two Stall Protection Modules (SPM 1 and SPM 2) calculate when the
aircraft is approaching a stall condition and determine when to activate and cancel
both stick shaker and stick pusher operation.
B. Stall Protection Modules (SPM)
1. SPM1 and SPM2 use the following parameters to determine an approaching
stall condition and the need for stick shaker activation:
• Angle of attack data – the average of two Angle of Attack(AOA) inputs
• Flap position – input from Flap Position Indication Unit
• Mach number – input from ADU 1 & 2
• Engine torque
• Icing status – input from the REF SPEEDS switch
When the SPM’s detect an impending stall condition they activate their related
stick shaker and signal the Automatic Flight Control System (AFCS) to
disengage the autopilot.
2. SPM 1 and SPM 2 use the following parameters to determine when stick pusher
operation needs to be activated.
• Angle of attack – the average of two Angle of Attack(AOA 1/AOA2) inputs
• Flap position – input from Flap Position Indication Unit
• Mach number – input from ADU 1 & 2
• Power lever angle
• Condition lever angle
• Icing status – input from the REF SPEEDS switch
C. Stall Protection System Operation
The Stall Protection System operates when the conditions that follow are met:
• Calibrated airspeed (true) is less than 215 knots
• Altitude is more than 500 feet AGL
• The Stick pusher SHUT OFF switchlight is not pushed to the OFF position