General Principles - Landing — Page 289, Lesson 363

I want to walk you through the microburst — the single most hazardous weather phenomenon to aeroplanes close to the ground, particularly during the landing phase. Let's start with the warning signs, because that's where survival begins. The most obvious clue to a potential microburst is what you see beneath a storm cloud: tendrils of rain called virga, or fallstreaks. Virga is precipitation that is falling but evaporating before it reaches the ground. So you see rain streaks hanging from the cloud, but nothing wet reaching the runway. That's your advance warning that a microburst may be lurking. Now, let's trace what happens when you actually fly into one on approach. Initially, you'll get an increase in airspeed and a rise above the approach path, caused by the increasing headwind. On modern aeroplanes, a windshear alert is usually given at this point. Treat that alert as the precursor to the microburst. The moment you see it, abandon any hope of a stabilized approach and initiate a missed approach immediately. Here's the technique. Without hesitation, increase power to go-around power, raise the nose, and fly the aeroplane in accordance with the missed approach procedure. Typically the nose attitude will be about 15°, and you hold the control column against the buffet or stick shaker — that's the stall warning. You're riding right on the edge of the stall to get maximum performance. Now here's the trap. That initial bonus of increased airspeed gets rapidly eroded as you encounter the downdraught. Airspeed falls, and the aeroplane may start to descend despite high power and high pitch angle. The most critical point is when the tailwind starts to be encountered. Your rate of descent may reduce, but the airspeed may continue to fall, and any height loss may now break into your obstacle clearance margins. At this stage you need maximum thrust, and you keep the nose attitude high on the stall warning margins to escape the tailwind's effects. Let me be blunt about the stakes. Had the go-around not been initiated at the early warning stage, it is highly unlikely the aeroplane would survive the encounter. That's how severe this is. Now, the broader lesson. Windshear, heavy rain, poor visibility, runway contamination, and microbursts are all hazards very closely associated with thunderstorms. So the professional rule is simple: never land with a thunderstorm at or in the immediate vicinity of the aerodrome. Delay the landing, or consider diverting. There are too many cases to list of pilots who attempted to land in bad weather and perished along with many passengers. Most of those occurrences were avoidable had due account been taken of the situation. So the whole philosophy here is: the microburst is survivable only if you act on the early clues — the virga, the windshear alert, the initial airspeed increase — and commit to the missed approach without hesitation. That's the difference between a professional decision and a tragedy.