ILS Approach with Wind Shear and a Failing Localizer Indication
You are flying an ILS approach to a runway with a published decision altitude of 200 ft AGL. Reported surface wind is 250°/18 kt gusting 30 kt; the runway is 27 (270°). On short final at 600 ft AGL the localizer needle begins to drift and the glideslope shows a brief fly-up command, then both settle. You are visual with the runway. Tower reports a recent wind shear alert. Your aircraft is at approach speed with landing flap set; a go-around would require a clean-up and re-approach with about 15 min of fuel above reserve.
1. Interpret the localizer/glideslope behaviour and decide whether to continue or go around.
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A localizer drift plus a transient fly-up on the glideslope, coincident with a reported wind shear and gusty crosswind, is most consistent with wind shear/turbulence disturbing the approach path, not necessarily an equipment failure. The fact that both indications settled supports a transient shear rather than a failed ground station.
However, the approach is now unstable in the critical final segment, and the shear alert is active. The conservative and standard response is to go around, clean up, and either re-approach when the shear has passed or divert. Continuing below 600 ft AGL with an unresolved shear and a drifting localizer is not defensible. Fuel allows one re-approach with margin.
2. If you go around, describe the wind shear escape technique and the configuration sequence.
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- Apply go-around power immediately and set the attitude for the go-around; do not chase the glideslope.
- Pitch for the escape attitude (typically the manufacturer's wind shear escape pitch) and accept a temporary airspeed loss rather than pitching down into the shear.
- Do not change configuration (gear/flaps) until clear of the shear and established in a climb - retracting flaps in a shear can cause a sink.
- Maintain maximum available thrust and monitor airspeed and vertical speed; once positively climbing, clean up per the go-around procedure.
- Advise ATC of the go-around and the reason (wind shear).
3. Explain how the gust factor and crosswind component affect your landing performance calculation and decision to land.
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Wind 250°/18G30 on runway 27 gives a crosswind component of about 18 kt × sin(20°) ≈ 6 kt, gusting to about 10 kt - within typical limits, but the gust factor (12 kt) means airspeed will fluctuate. Add half the gust factor to the approach speed (about +6 kt) to improve gust penetration and reduce the risk of a stall on a shear encounter.
The gusty crosswind also increases the risk of a bounced or drifted landing, which is why a stable approach to a firm touchdown is preferred over a float. If the approach cannot be stabilized by the decision altitude, go around. Landing distance should be calculated with the gust factor and any contaminated runway allowance; if the margin is thin, divert.