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Many aircraft accidents have been caused by downbursts. A downburst is basically a strong downward wind that forces the aircraft toward the ground and causes it to crash. Is it possible for an airliner to escape the downburst and land safely with this much force pushing down on an aircraft?

Here is a downburst illustration: enter image description hereSource:(www.mikesmithenterprisesblog.com)

digitgopher
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Ethan
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2 Answers2

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First take a look http://www.erh.noaa.gov/cae/svrwx/downburst.htm for info on downbursts.

An aircraft encountering a microburst (the more localized form of a downburst and that which airline crews train for) can counter it in two basic ways:

  1. establish, if possible, a climb rate through the descending air that is greater than the downward vertical speed of the air.
  2. fly through the column of descending air to air that is not descending or is at least descending at a lesser rate

And, of course, do this without stalling the airplane, especially as you come out of the burst. A practical scenario is that your max climb rate through the descending air can at least reduce your descent rate toward the ground enough that you will be able to transit the burst before hitting the ground.

I was never in a full blown microburst for real, but I practiced recovering from them many times in simulators. For 747-100/200 aircraft in the 1990s the procedure was:

  1. thrust levers all the way forward
  2. raise the nose until you get the stick shaker
  3. fly the aircraft straight ahead while keeping the speed solidly in the stick shaker range.
  4. do not change the aircraft configuration, in other words don't mess with the flaps or the gear.

In simulators it's a wild ride. You can tell how far into the stick shaker range you are by the frequency of the shaker by feel and by its noise. The closer you get to an actual stall, the faster the stick shaker will go, so the idea was to keep the shaker on but not too fast. Since the airspeed will be varying rapidly, you have to do that with large pitch changes.

There was controversy back in the 1990s as to whether what we were trained to do was actually the best way, especially as to not changing the aircraft configuration and how deep to go into the stick shaker. Perhaps now the thinking is different.

Terry
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    I had a sim check where the check airman gave me a microburst in the turn to final over the potomac going into DCA runway 19. Rolled level but wasn't quite aligned with the runway riding the stick-shaker with max available thrust. I saw the RA clicking ever lower and my FO claimed it read "5" before positive rate was established. I was absolutely sure I was going hit the ground and readying to stop ASAP to avoid overrunning into the river. fun checkride. – casey Oct 03 '15 at 04:22
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    I don't think the procedures are much different now. Put as much energy into the plane as possible so you have enough to stay above ground. Makes sense. If you change configuration like raising the gear, you will add more drag for several seconds, and this might be too much - after all, microbursts are a short-time event, so transition effects are important. – Peter Kämpf Oct 03 '15 at 09:17
  • Is it then a better pratise to avoid situations like above, or do pilots have no otpion but to go through them. – Firee Oct 05 '15 at 14:35
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    @Firee When the safety of the aircraft is involved, pilots have the authority to do whatever they believe is safest. However, in the case of microbursts, it's not the case that you can know one is in front of you and are deciding whether or not to penetrate it. No pilot would do that. You don't know you're in a microburst until you're already in it. Then, of course, you have no option but to continue until you're through it. Microbursts are relatively rare. In 30 years of flying I never encountered one. – Terry Oct 05 '15 at 18:58
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    @Firee the only place you are going to get quick and reliable detection of an event like this is a big airport with anemometers around the airport perimeter. These will also only detect wild wind differences once the event is in progress (the downdraft core precedes the surface boundaries) and unless the core is over the airport the wind signature wont be as clear. Basically, unless you are somewhere you shouldn't be (under a well developed thunderstorm or virga) you may have no warning of a microburst event until the plane starts complaining that you are in one. – casey Oct 06 '15 at 15:12
  • Terry & Casey: I think both your comments have answered my query, that its unlikely that a pilot would come to know about it beforehand. – Firee Oct 07 '15 at 09:34
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'this much force' - how much force? Down bursts vary in size, location and intensity.

An airliner encountering an intense downburst just off the end of the runway will almost certainly crash as there will be insufficient time for the crew to recover.

The same aircraft encountering a less intense event some distance from the threshold at, say, 2000' may give the passengers an exciting ride but may be able to recover.

It all depends...

  • downburst Here's your answer of how powerful. – Ethan Oct 03 '15 at 02:48
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    @Ethan, that's not a clarification. Airsick is totally correct that downbursts vary in intensity. You're basically saying, "can a boat sail through a wave?" Are we talking once-a-century rogue waves, the things people surf on, or waves on a small lake? You need to use a specific example, or we can't provide you with a specific answer. – egid Oct 03 '15 at 02:59