Definition

An airborne wind shear warning system is a device which identifies the presence of wind shear.

Description

Some systems detect a potentially severe windshear phenomena far enough in advance of the encounter, in both the takeoff/climbout profile and the approach/landing profile, to allow the pilot to successfully avoid the phenomena.

Other systems provide the pilot with timely warning and adequate flight guidance, in the event of severe wind shear, to fly a successful escape manoeuvre:

1. Approach/Missed Approach: using the maximum performance capability available without inadvertent loss of control, stall, and without ground contact.

2. Takeoff and Climbout: during the initial or subsequent climb segments using the maximum performance capability available without inadvertent loss of control or ground contact with excess energy still available.

Early systems relied on aircraft sensors to determine the presence of wind shear. These systems were of limited value as they were unable to predict the onset of wind shear. Later systems use doppler weather radar, or other systems such as laser or infra-red technology to predict wind shear.

Many modern aircraft, such as the B777 Series, have Predictive Wind Shear (PWS) warning systems which collect wind velocity data gathered by the weather radar to identify the existence of wind shear. These systems have a short range, and are dependant on the radar picking up velocity data from water and ice particles ahead of the aircraft and, consequently, don’t work in dry conditions. However, they are effective, providing the pilot with an opportunity to abort the take-off or carry out a missed approach.

Some versions of Terrain Avoidance and Warning System (TAWS) also provide windshear warning.

Employment

Operators provide specific guidance to flight crews on how to respond to wind shear cautions and warnings. For example, standard operating procedures (SOPs) might state that on approach, a crew might continue the approach in the event of a wind shear caution, as long as the approach remains stable. But SOPs normally say crews must go around in the event of a wind shear warning. Depending on equipment model, various parameters will establish the distinction between a caution and a warning. For example, an increasing headwind above a certain limit might trigger a caution, while an increasing tailwind will trigger a warning.

Further Reading

UK CAA

Safety Notice: Missed Approaches in Response to Onboard Windshear Alerts, 04 June 2013