M1, S2, C4 - Windshear

Question 1

Wind shear is…

Answer 1

…a sustained change in the wind velocity along the aircraft flight path, which occurs significantly faster than the aircraft can accelerate or decelerate

Question 2

Wind shear can occur…

Answer 2

…at any level, but it is low level wind shear, occurring from the surface to a height of approximately 1500ft which can cause problems of sufficient magnitude to affect the control of aircraft in departure or final approach phases of flight

Question 3

Controllers should be alert to the possibility of the existence of wind shear in the following circumstances:

Answer 3

1) the presence of frontal/squall/thunderstorm activity in the vicinity of the aerodrome
2) the presence of low level inversions where the surface wind will be significantly different from that at only a few hundred feet above the ground
3) local terrain or buildings considered in relation to wind speed and direction; such large obstructions can cause wind shear as well as the more usual turbulence and gusts

Question 4

Due to the need to maintain both a safe margin above the stalling speed and a clearly defined flight profile, particularly during the climb out and approach phases of flight, sudden changes in airspeed must be countered very rapidly.

If the aircraft is in a turn when a wind shear alert is generated…

Answer 4

…the crew may level the wings to maximise the climb gradient, unless a turn is required for obstacle clearance.

Furthermore, due to high flight deck workload the reply ‘standby’ in response to ATC instructions is not unusual during such events.

Question 5

Pilots will continue to fly the wind shear recovery manoeuvre until…

Answer 5

…the onboard system ceases to annunciation the wind shear alert, and may therefore require deviation from their clearance.

Question 6

Onboard wind shear alerts take precedence over…

Answer 6

…TCAS annunciations and due to the high flight deck workload during wind shear recovery manoeuvres the TCAS display may not be monitored to the same extent as during normal ops.

Question 7

Rates of climb during wind shear recovery manoeuvres, which employ the use of maximum thrust, will…

Answer 7

…significantly exceed hose during missed approaches executed for reasons such as an occupied runway, or lack of visual contact due to poor visibility.

These high rates of climb, especially when associated with a missed approach which has a relatively low level-off altitude, can result in pilots exceeding their cleared level and eroding separation from other aircraft.

Question 8

In the event of a pilot executing a missed approach due to a wind shear alert, controllers should be prepared for the aircraft to…

Answer 8

…exceed the missed approach altitude.

Controllers should provide enhanced traffic information as necessary and provide instructions and advice as deemed appropriate to ensure safety.

Question 9

Whenever a pilot reports wind shear conditions to ATC the information shall be…

Answer 9

…relayed to subsequent inbound and outbound aircraft until confirmation is received that the condition no longer exists

Question 10

Wind shear reports from pilots should contain the following information:

Answer 10

1) warning of the presence of wind shear
2) the height or height band where the wind shear was encountered
3) the time at which it was encountered
4) details to the effect of the wind shear on the aircraft eg speed gain or loss, vertical speed tendency, change in drift

Question 11

At aerodromes where ATIS is available, wind shear information may be…

Answer 11

…included in the broadcasts.

Controllers should amplify the information for individual aircraft if necessary.