By The CTS Team on July 31, 2017
Category: Aviation Weather

Facing the wind: Decisive maneuvers in windshear encounters

Recovery techniques, avoidance, and knowledge must combine in the face of windshear encounters.

This month's CALLBACK from NASA ASRS discusses several windshear encounter stories from pilots, along with their choices and thought processes along the way. All of these anecdotes have clear, useful lessons about the relationship between pilots, windshear, and decision-making, but we want to focus on the first of the stories: "Teasing a Toronto Tailwind." Here, an A319 pilot encounters windshear during heavy rain and moderate turbulence, resulting in an unstable approach. Then, he makes a series of calls as to how to handle the event:

After being delayed due to low ceilings in Toronto, we were finally descending…in heavy rain and moderate turbulence with clearance to 7,000 feet MSL. After a third 360 degree turn, we were…transferred to the Final Controller and proceeded inbound for the ILS RWY 05. The last several ATIS [reports] showed winds at approximately 090 to 100 [degrees] at 5 to 10 knots, and the Final Controller mentioned the same with an RVR of 6,000 plus feet for Runway 05. When cleared for the approach, we were at 3,000 feet MSL to intercept the glideslope, and I noticed the winds had picked up to a 50 knot direct tailwind. The First Officer was flying. We were assigned 160 knots and began to configure at approximately 2,000 feet AGL. At 1,500 feet the wind was a 30 knot direct tailwind and we had flaps 3. Indicated airspeed (IAS) had increased at this point [with] thrust at idle to 170-175 knots, prohibiting final flaps just yet. The First Officer did a great job aggressively trying to slow the aircraft, as we were concerned about getting a flaps 3 overspeed. As I knew from the ATIS and the Controllers (Tower now), the winds were to die off very soon to less than 10 knots. [Below] 1,000 feet we were just getting the airspeed to put in final flaps (full) and were finally stabilized and on speed between 500 to 800 feet. The winds were now at the reported 090 [degrees] at 8 knots or so [below] 500 feet. The total wind shift was approximately 90 degrees from direct tailwind to a right crosswind - losing 40 knots [of tailwind] in the space of 1,500 feet or so.
The reasons I elected to continue the approach were:
1. [I knew] about the wind shift and decrease [in tailwind] as reported on the ATIS and from ATC.
2. [I saw] a positive trend in the wind.
3. [I was] prepared for the missed approach (at 500 feet) IF the winds and IAS stayed as they were earlier in the approach.

Here, we have a pilot who deliberately opts to continue an approach into potential windshear for a variety of reasons: he recognizes that the problem wind is about to dissipate; he is confident his aircraft can make the landing if conditions do not drastically worsen; he is prepared to take the missed approach if windshear becomes a problem. The result was a completely uneventful landing (not shown in the excerpt above).

If you balked at the conditions for the approach, then obviously the go-around was the correct decision. With an airliner like an A319, the options available to a pilot may be different than what might be available to a smaller aircraft. But the takeaway here isn't what the A319 can or can't do. What is notable in this story is the way the pilot made a clear, decisive choice devoid of panic response or doubt, and left himself an out he knew he could take if things did not turn out the way he planned. Waffling and uncertainty in such situations can waste valuable time, landing a pilot in a situation where a decision has already been made for them.

Whether your choice is a go-around or a continued approach, these kinds of quick, firm decisions are necessary to avoid windshear encounters. But the ability to make such decisions hinges upon your own knowledge: how often have you practiced recovery techniques? How well do you understand the conditions most closely tied to windshear? When looking at a weather map, do you see the possibility for windshear when looking at a fast-moving front with a wide temperature difference, or a forming thunderstorm?

Simulator time and regular practice can help you better understand how your aircraft will handle, giving you confidence to make the right decisions when windshear possibilities become a reality. Above all, remember that the best defense against windshear is avoiding it altogether, making your decision-making easier than you might think: If you are ever in doubt, don't hesitate. Go around or otherwise adjust your flight path to avoid the hazards of windshear, and always leave an out. After all, the best windshear recovery techniques are ones that are well-practiced, but that you never have to use.

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