I flew from Frankfurt to Madrid earlier this week, as airline passenger, and my flight was delayed by forty minutes. The passengers were informed only once boarding was completed and the official reason was “wind in Madrid”. This sounds strange, and I had plenty of time, seating in an Airbus 319 to check the latest METAR of Madrid via www.easymetar.com. The wind part of the METAR was uncommon: “34020KT WS R33L WS R33R”. At the next updated, it was reading “340030KT WS ALL RWY”.
WS ? Windshear. An abrupt change in wind direction and speed over a short distance. Windshears are can be caused by different factors, including jet streams, mountain waves, and cumulonimbus. Windsears are hazardous for aircraft because they can strongly impact the climb or descent performance within seconds. A typical windshear starts with increase of headwind and updrafts, and continues with tailwind and downdrafts.
Downdrafts and low altitude are not exactly a good combination, and windshears hard to forecast and measure. Modern aircraft are equipped with windhsears detectors and give warning to the flight crew when such conditions are encountered. Click here to see a (non-embeddable… grrr) video describing the windshear feature of an EGPWS system from Honeywell. As the comment says, “recovery shall be continued until reaching a safe altitude over ground”. Recovery normally means apply full power, raise the aicraft’s nose, and climb.
Check the evolution of the speed, and the speed prediction – the yellow arrow on the speed tape – in this video. At one moment, shortly before the captain applies TOGA (Take-Off / Go-Around) power, the predicted speed reaches values below the stall speed!
Click here to read more about Winshear Awareness from Airbus.
My flight was delayed because the airport reduced the number incoming flights to account for a higher than normal number of go-around and consecutive extra approaches. Finally, the flight was fine, some bumps on the approach, but no go-around and no windshear.
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I have to admit, I would have had to look up WS. I should probably bone up on my metar/taf translation abilities!