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heavy turbulence in cruise.
WINDSHEAR
Applicable to: ALL
BACKGROUND INFORMATION
WINDSHEAR PHENOMENON
Windshear is mainly due to a cool shaft of air, like a cylinder with a width between 0.5 nm and
1.5 nm, that is moving downward. When the air hits the ground, it:
• Mushrooms horizontally, causing horizontal wind gradient
• Curls inward at the edges, causing vertical air mass movement.
Flight safety is affected, because:
• The horizontal wind gradient significantly affects lift, causing the aircraft to descend, or to
reach a very high AOA.
• The vertical air mass movement severely affects the aircraft flight path.
Windshear Phenomenon
AWARENESS AND AVOIDANCE
Awareness of the weather conditions that cause windshear will reduce the risk of an encounter.
Studying meteorological reports and listening to tower reports will help the flight crew to assess
the weather conditions that are to be expected during takeoff or landing.
If a windshear encounter is likely, the takeoff or landing should be delayed until the conditions
improve, e.g. until a thunderstorm has moved away from the airport.
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
ADVERSE WEATHER
A330/A340 FLEET SI-010 P 11/16
FCTM 17 JUN 09
STRATEGY FOR COPING WITH WINDSHEAR
Windshear and microburst are hazardous phenomena for an aircraft at takeoff or landing. The
strategy to cope with windshear is:
• Increasing Flight Crew Awareness through the Predictive Windshear System (PWS)
• Informing the Flight Crew of unexpected air mass variations through FPV and approach
speed variations
• Warning the flight crew of significant loss of energy through "SPEED, SPEED, SPEED" and
"WINDSHEAR" aural warnings
• Providing effective tools to escape the shear through ALPHA FLOOR protection, SRS pitch
order, high AOA protection and Ground Speed (GS) mini protection.
Increasing Flight Crew Awareness
When the airshaft of a microburst reaches the ground, it mushrooms outward, carrying with
it a large number of falling rain droplets. The radar can measure the speed variations of the
droplets, and as a result, assess wind variations. This predictive capability to assess wind
variations is performed by the Predictive Windshear System (PWS). The PWS operates
automatically below 2 300 ft AGL, regardless of whether the radar is turned on or off.
Informing the Flight Crew
The FPV associated with the approach speed variations (GS mini protection) is an effective
means for informing the flight crew of unexpected air mass variations:
Approach speed variations and lateral FPV displacement reflect horizontal wind gradient.
Vertical FPV displacement reflects the vertical air mass movement.
bird and target speed - wind interpretation
Warning the Flight Crew
The "SPEED, SPEED, SPEED" low energy warning is based on the aircraft speed,
acceleration and flight path angle. This warning attracts the PF’s eyes to the speed scale,
and requests rapid thrust adjustment. In windshear conditions, it is the first warning to appear,
before the activation of the alpha floor protection. The following table provides some typical
values of the speed at which the warning could occur in two different circumstances.
A330/A340 FLIGHT CREW TRAINING MANUAL
SUPPLEMENTARY INFORMATION
ADVERSE WEATHER
A330/A340 FLEET SI-010 P 12/16
FCTM 17 JUN 09
Deceleration Rate Flight Path Angle Warning
-1 kt/second -3 ° VLS -7 kt
-1 kt/second -4 ° VLS -1 kt
In addition, the aircraft has a reactive windshear warning system. This system triggers if
the aircraft encounters windshear. In such a case, there is a "WINDSHEAR WINDSHEAR
WINDSHEAR" aural warning.
Providing Effective Tools
There are three effective tools to assist the flight crew to escape:
• The alpha floor protection
• The SRS AP/FD pitch law
• The high angle-of-attack protection.
When the alpha floor protection is triggered, the A/THR triggers TOGA on all engines. The
FMA displays A FLOOR, that changes to TOGA LK, when the aircraft angle-of-attack has
decreased. TOGA/LK can only be deselected by turning the A/THR off.
The SRS pitch mode ensures the best aircraft climb performance. Therefore, the procedure
requests following the SRS pitch bar and possibly full aft stick, in order to follow the SRS
orders and minimize the loss of height.
The high angle-of-attack protection enables the PF to safely pull full aft stick, if needed, in
order to follow the SRS pitch order, or to rapidly counteract a down movement. This provides
maximum lift and minimum drag, by automatically retracting the speed brakes, if they are
　
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