OPERATIONS MANUAL

Warning Systems
Predictive Windshear System:
General
Unlike the reactive windshear system of the EGPWS, the predictive
windshear system (PWS) is a function of the weather radar system and
is able to alert the crew before a windshear zone is entered. It shows the
detected windshear zones on the NDs, and triggers aural alerts when a
windshear zone is located near the current flight track.
Technology
The PWS can detect windshears only in areas where precipitation exists. The
radio frequency of radar returns from water drops is higher when the drops
move toward the aircraft, and is lower when moving away from the aircraft
(Doppler effect). This way, the radar system can compute the speeds of air
masses at several locations within the scope of the radar.
Enablement
The PWS is enabled when any of these conditions is true:
• Aircraft is in flight and below 2300 ft RA.
• Aircraft is on the ground and takeoff thrust is set.
• Aircraft is on the ground and WXR is selected on the EFIS control.
When initially enabled on the ground, it may take up to 12 seconds of
sweep time until the radar can provide windshear alerts for the area ahead.
Therefore, when windshear conditions exist, the crew should manually
activate the radar as soon as the takeoff position is reached; the automatic
enable logic by takeoff thrust detection is just a backup function.
Alerts
The PWS can generate alerts when the aircraft is below 1200 ft RA. When
WXR is selected on the EFIS control, pushing the TEST switch on the
weather radar control panel starts a radar test; this will include an alert
system test. Windshear zones appear on the ND maps in form of redstriped
sectors accompanied by amber radials at the sector edges. There
are two alert levels: caution level and warning level. The level depends on
the location of the predicted windshear zone. The NDs show the word
WINDSHEAR in amber or red according to the alert level. The red master
warning lights illuminate for warnings.
Aural messages sound in the following cases:
• “Monitor radar display!” for cautions in all flight phases.
• “Windshear ahead! Windshear ahead!” for warnings during takeoff roll.
• “Go around! Windshear ahead!” for warnings during the landing.
• “Radar test terminated!” when switching off a test before the system has
completed the test.
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