A decrease in angle of attack means a loss of lift — Page 181, Lesson 277

I want to walk you through a critical part of low-level flying — what happens when windshear or a microburst catches you near the ground, and how you must react. Let's start with the aerodynamic effect. When the relative airflow changes direction — which is exactly what happens in windshear — it alters the angle of attack of the wing. A decrease in angle of attack means a loss of lift. And that is not desirable near the ground, where you have very little height and time to recover. Below 1,000 feet, the risk of a downdraught — air pushing the aircraft downward — is more likely than an updraught. So the threat is real and immediate. Now, the vital actions to counter the loss of airspeed and lift caused by windshear near the ground are three, and they must be done briskly. First, briskly increase engine power — go to full power. Second, raise the nose to check the descent. EU-OPS recommends 15 degrees nose-up, unless the aircraft manufacturer states otherwise. Third, co-ordinate power and pitch — you need to manage them together, not one after the other. And be prepared to carry out a missed approach rather than risk landing from a destabilised approach. If the approach is not stable — meaning your speed, path, and configuration are not settled — it is safer to go around. Let's move to the microburst situation. A microburst is a concentrated, violent downdraught that spreads out when it hits the ground. The sequence you will encounter is: first, an increasing headwind, then a downdraught, then an increasing tailwind. That combination produces a temporary energy gain — the headwind gives you extra indicated airspeed — followed by an increasing energy loss as you hit the downdraught and then the tailwind. On any approach profile, the overall effect is to cause the aeroplane to sink below the glide path. But here is the trap: the first indication is the 'ballooning' — that energy gain makes the aircraft rise or feel fast. If you react to counter that energy gain — for example by reducing power or pushing the nose down — that action will be potentially disastrous, because it will compound the energy loss that follows shortly afterwards. You will have already reduced your margin. A successful escape from a microburst depends on three reserves: adequate reserve of engine power, adequate reserve of height, and adequate reserve of speed. If your flight path goes through the periphery — the edge — of the microburst, lateral displacement will add to the problem, especially if you are trying to line up with the runway. The best defence is to expect the unexpected and know the signs of potential microburst or windshear activity. Finally, the book gives you the decision-making framework. If, after carefully assessing all available information, you decide to continue the approach to land or to proceed with the take-off, you should prepare for possible windshear encounters by taking the precautionary actions specified in the aircraft operating manual — the OM — and in the airline company flight manuals. But remember: avoidance is the best precaution. If you can avoid the condition entirely, that is your safest option.