Science Why are microbursts a hazard to aviation?

Other answer:

Kennedy:
They combine three hazards, strong headwinds, strong downdrafts and strong tailwinds, all in one neat little package!

A microburst is a very powerful downward current of air coming from the bottom of a thundercloud, in some ways it is the reverse of a tornado. When it hits the ground it gets spread out as a toroidal ring of fast moving air.

As an aircraft approaches the ring, it first of all meets a very strong headwind, which is curling upwards like a wave. This causes the aircraft to pitch up and climb steeply, disturbing the approach path and the stability of the airspeed, It then reaches the major downdraft, which slams it towards the ground, causing the pilots to haul back on the controls to avoid the ground and reducing airspeed. It then reaches the most dangerous phase, a very strong tail wind.

This is the hardest part of the process to understand, but to explain it simply, the aircraft is flying through air, which is what causes lift. With normal variations of wind speed the aircraft hardly notices the change and is, in any event, flying fast enough that it makes no practical difference.

When it hits the tailwind from a downburst, the wind can change from an apparent 150 knot headwind/airspeed to a 100 knot tailwind in an instant, leaving the aircraft with only an effective 50 mph apparent airspeed. The aircraft cannot fly at that airspeed and will stall.

If it has insufficient height to recover and insufficient time for the engines to spool up to accelerate the aircraft, the aircraft will crash.

Skipper747:
With a "windshear" (the way pilots and tower controllers call microbursts) you could crash –
Imagine you have a 60 knots loss during the approach, headwind to tailwind –
Airliners approach at a maximum of 20 knots added to the approach speed for their weight –
Typical approach speed is normally 30% above stall speed (about 90 knots for a 737) –
In most "extreme headwinds" pilots approach 20 knots faster than the "no wind" Vref –

During the approach the 737 might fly at 90 + 27 + 20 = 137 knots –
Then suddenly with windshear, the speed will fall to 137 – 60 = 77 knots = stall = crash –

Paige:
Microbursts are kind of violent with really strong wind shear forces. Those forces can, and do, start to rip vital parts from the airframe.
Christopher:
Microbursts are kind of violent with really strong wind shear forces. Those forces can, and do, start to rip vital parts from the airframe.
Lauren:
Microbursts are kind of violent with really strong wind shear forces. Those forces can, and do, start to rip vital parts from the airframe.
Aviation:
Microbursts are kind of violent with really strong wind shear forces. Those forces can, and do, start to rip vital parts from the airframe.
Ianab:
Because they involve sudden up-draft / down-draft and wind shear situations.

So a plane coming in to land can suddenly go from a 60 mph headwind, to a 60 mph tailwind, in a couple of seconds. This suddenly drops it's air speed to below a stall, the plane drops like a rock, and being so close to the ground it can crash before the crew or autopilot has the chance to recover.

Federico:
microbursts are kind of violent with really strong wind shear forces… those forces can, and do, start to rip vital parts from the airframe…
Luca:
'cause they involve sudden up-draft / down-draft and wind shear situations…

so a plane coming in to land can suddenly go from a 60 mph headwind, to a 60 mph tailwind, in a couple of seconds… this suddenly drops it's air speed to below a stall, the plane drops like a rock, and being so close to the ground it can crash before the crew or autopilot has the chance to recover…

Gabriele:
microbursts are kind of violent with really strong wind shear forces… those forces can, and do, start to rip vital parts from the airframe…