Warning Systems - Windshear

Windshear Warning System

The GPWS takes additional data from the stall warning computer (STC) and determines if windshear conditions are occurring in the immediate vicinity of the airplane.

In addition, the GPWS computer takes weather radar data and determines if windshear conditions are occurring ahead of the airplane track.

Windshear Immediate-Alerts

GPWS issues Windshear Immediate-Warnings whenever decreasing-performance windshear conditions are present during takeoff, approach and landing.

Windshear warnings are accompanied by:

If illuminated, pushing a Master WARNING/CAUTION reset switch resets the Master WARNING lights but does not deactivate the windshear warning.

Windshear Immediate-Alert Warnings

Aural Alert Visual Alert Description
Two-tone siren
followed by
WINDSHEAR sound clip
Windshear Alerts

Master WARNING lights

Red WINDSHEAR on both ADIs

Excessive windshear at the current airplane position

Enabled below 1,500 feet Radio Altitude

GPWS Windshear detection begins at rotation

Predictive Windshear (PWS)

The weather radar provides predictive windshear (PWS) alerts when it detects disturbed air ahead of the aircraft which contains moisture or particulate matter and which fits a known pattern of windshear activity.

The PWS alert area ahead of the aircraft is shown as follows:

Predictive Windshear Alert Area.

When the PWS mode is enabled, the radar system is time-shared between the weather display and the PWS display. During the time-share:

  • the weather display is slower to update
  • PWS alerts are available approximately 12 seconds after the system begins scanning
  • PWS automatically, regardless of actual Weather Radar Control Panel settings, adjusts the antenna TILT and the system GAIN for optimum windshear detection

The PWS mode is automatically enabled when:

  • on the ground, the thrust levers are set for takeoff
  • in flight, the aircraft is below 2,300 feet AGL

PWS alerts are automatically enabled below 1,200 feet AGL.

If windshear is not detected, Weather Radar returns show only after pushing the EFIS control panel WXR switch.

PWS warnings are accompanied by:

  • visual alerts (see tables)
  • voice or aural alerts (see tables)

If illuminated, pushing a Master WARNING/CAUTION reset switch resets the Master WARNING lights but does not deactivate the windshear warning.

PWS caution alerts are accompanied by:

  • visual alerts (see tables)
  • voice or aural alerts (see tables)

Note: PWS does not provide alerting for all types of windshear. The flight crew must continue to rely on traditional windshear avoidance methods.

PWS Warnings

Aural Alert Visual Alert Description
WINDSHEAR AHEAD,
WINDSHEAR AHEAD

Red WINDSHEAR on both ADIs

Windshear Alerts

Master WARNING lights

RED and BLACK PWS symbol on HSI

Red WINDSHEAR message on HSI (all modes)

Predictive Windshear Display and Annunciation

Enabled during takeoff, below 1,200 feet AGL (Radio Altitude).

Windshear within 3.0 miles and directly ahead of the airplane detected by the weather radar.

PWS symbol on the HSI shows windshear position and size only when the HSI Mode Selector is in the VOR, APP, MAP or CTR MAP mode and the TERR switch is not pushed.

GO AROUND, WINDSHEAR AHEAD

Red WINDSHEAR on both ADIs

Windshear Alerts

Master WARNING lights

RED and BLACK PWS symbol on HSI

Red WINDSHEAR message on HSI (all modes)

Predictive Windshear Display and Annunciation

Enabled during approach, below 1,200 feet AGL (Radio Altitude).

Windshear within 1.5 miles and directly ahead of the airplane detected by the weather radar.

PWS symbol on the HSI shows windshear position and size only when the HSI Mode Selector is in the VOR, APP, MAP or CTR MAP mode and the TERR switch is not pushed.

PWS Cautions

Aural Alert Visual Alert Description
MONITOR
RADAR
DISPLAY

RED and BLACK PWS symbol on HSI

Amber WINDSHEAR message on HSI (all modes)

Predictive Windshear Display and Annunciation

Windshear within 3 miles and not directly ahead of the airplane.

Enabled during takeoff and approach, below 1,200 feet AGL (Radio Altitude).

PWS symbol on the HSI shows windshear position and size only when the HSI Mode Selector is in the VOR, APP, MAP or CTR MAP mode and the TERR switch is not pushed.

PWS Inhibits

PWS alerts are inhibited during takeoff and landing as follows:

  • WARNINGS, between 100 knots and 50 feet AGL
  • CAUTIONS, between 80 knots and 400 feet AGL

Note: These inhibits do not remove existing PWS alerts.

PWS alerts are also inhibited by

TCAS