Stall Warning Protection System Flashcards
What is the requirement for Stall Warning Protection Systems?
Aviation regulators require that all fixed wing transport aircraft must have safe pre-stall and stall recovery handling qualities.
What is the purpose of a SWPS?
To provide situational awareness of an approaching stall with a visual indication of the approaching stall in the Low Speed Awareness (LSA) zone of the ASI tape on both PFDs and an unambiguous aural warning that the aircraft is approaching the stall.
To prevent the aircraft from entering a potentially hazardous, high AoA deep stall by means of a Stick Pusher Actuator (SPA) which causes the aircraft to pitch down, reducing AoA.
What parameters does the SWPS receive?
The SWPS receives parameters such as airspeed/Mach, acceleration, flap position, de-icing system status, landing gear position and WOW to establish Green Circle and Low Speed Awareness (LSA) visual ques, aural stall warnings and SPA activation.
What are the components of the SWPS?
SWPS Computer
Stick Push Actuator
Two AoA Sensors
Pusher Cut-out
Test Button
When does the stick pusher not actuate?
On the ground except during test
Below 0.5 g
Within 20 s of take-off
If the Pusher Cut-out is pushed in
If at least one SWPS computer channel is inoperative
What does the green circle mean on the ASI?
It is 1.3x above the stalling speed. Fluctuates based on AoA.
What are the issues with the Initial Stall?
As increasing AoA causes drag to increase faster than lift, the aircraft enters a high rate of sink, further increasing AoA with no visual change in attitude.
What is the SWPS Computer?
A dual system, with two channels, installed in the Central Electronic Rack at the rear of the cabin. A crosslink is provided to share and compare data between the two SWPS computer channels. Each channel receives data from its respective AoA sensor and compares this with the other channel to produce an average AoA, compensating for any sideslip influence.
How is the SWPS Computer powered?
SWPC Channel 1 is powered by 28 Volt DC Bus 1. SWPC Channel 2 is powered by 28 Volt DC EMERG Bus.
How does the Stick Pusher Operate?
Stick push actuator - The SPA is a clutched electric motor located in the aircraft nose below the control yoke pedestal and connected by a steel cable to the elevator control system. To reduce the risk of inadvertent actuation, the stick pusher command is sent to the clutch through SWPC Channel 1 and to the motor through SWPC Channel 2.
When activated how does the Stick Push Actuator operate?
When activated, the SPA moves the control yokes forward to deflect the elevator trailing edge down. The SPA pushes forward with approx. 150lb of force, which ensures it cannot be countered by the pilot. However, the pilot can move the control column forward beyond the SPA limit.
How is the SPA powered?
28V DC Bus 2.
What is the purpose of the Pusher Cut out?
To disconnect the system in case of failure, the SWPS panel provides one cut-out button for both channels.
What happens when the IAS decreases towards the yellow band of the LSA zone?
As the IAS approaches the yellow band of the LSA zone, an aural warning, “INCREASE SPEED” will sound. The ‘INCREASE SPEED’ aural warning will only sound when the aircraft is in the ‘clean’ configuration.
What happens when the ASI moves into the Yellow band?
If the indicated airspeed is within the yellow range, the airspeed pointer is displayed in yellow.
