Systems Guide

A318/A319/A320/A321
Professional
SYSTEMS
Systems guide
Vol
4
04-03-15
11 July 2018
ALPHA FLOOR
The alpha floor protection assists the pilot in recovering from dangerous low speed and high angle of
attack by automatically setting TOGA thrust when:
• Excessive angle of attack (alpha)
• Excessive high nose up attitude
• Windshear is detected
When the alpha floor conditions are no longer detected the autothrust system will stay in TOGA lock until
the pilot disables auto throttle. It is recommended the pilot moves the throttle to the TOGA detent before
depressing the FCU A/THR pb to avoid a power surge. After that the pilot can pull the throttle to the CL
indent and engage the autothrust.
FLIGHT AUGMENTATION COMPUTERS
The FACs handle:
• Yaw damping and turn coordination
• Rudder trim
• Flight envelope and maneuvering speed computations
• Alpha floor protection
• Windshear detection
• Low energy detection
FLIGHT ENVELOPE
Many different speeds are calculated by the FACs are used by the autoflight system. These speeds include
the minimum safe speed, maximum speed and never exceed speed. They also calculate the alpha floor
speed. Most of these speeds are shown on the PFD airspeed indicator.
WINDSHEAR
The FACs will try to detect windshear and will warn the pilot of this dangerous condition. Windshear
detection is only active below 1300 feet AGL in configuration 1 or greater. When detected the flight
director will show an optimal pitch attitude and the aural warning “WINDSHEAR” will be heard.
LOW ENERGY WARNING
Between 2000 and 100 feet AGL the FACs will detect a low energy state (based on airspeed, descent angle
and angle of attack) and will warn the pilot with an aural “SPEED SPEED SPEED” warning. Normally this
warning will precede an alpha floor condition.