Saturday, August 22, 2015

The deadly danger of microbursts

I'm obliged to an anonymous reader for sending me the link to the first video below.

Microbursts pose a deadly danger to aircraft on final approach to a runway.  This video shows a microburst over Tucson, AZ earlier this month.  It's the clearest example I've ever seen of this weather phenomenon.  Watch it in full-screen mode for the best effect.

This is the sort of localized storm that brought down Delta Air Lines Flight 191 in 1985.  Here's an excerpt from a Smithsonian Channel documentary on the crash.

Miss D. informs me that it's actually easier to handle a microburst in a light aircraft like hers than it is for a jet airliner, because piston engines respond instantly to throttle demands, whereas jet engines have to 'spool up' to provide the thrust.  The slight delay while doing so can contribute to a crash.



On a Wing and a Whim said...

That said, Miss D here also noted that heavies have the advantage in dealing with turbulence, and that in general and specific, NO airplane wants to be anywhere NEAR a microburst.

Paul, Dammit! said...

It's VERY disconcerting on boats, too, to have the wind blow straight down, as radar is immediately gone in both s and x band, and more often than not this seems to happen close to shore, which means that draft issues and precision navigation are required, and it's not fun to be blown sideways when you're already in a narrow channel with just a foot of water under the keel (about normal for us when loaded).

Anonymous said...

While driving one sunny spring day I witnessed a flag snapping at its grommets blowing to the east when at 60 mph I came to an absolute standstill on the road bed. It was disconcerting to see in my rear view mirror the following traffic racing up my 6 o'clock until they too were caught by the sudden blast of the outflow of the microburst.

Only a few seconds later I was again moving along the road as if nothing happened...until I experienced and equally strong tailwind. Holy cow! Not only had I removed my foot from the accelerator but I began to brake in order to reduce my speed to manage the upcoming curve on this narrow highway. It was then I noticed a 2nd flag blowing just as strong but to the west.

As a pilot who flies mostly in the SW desert/mountainous terrain, I have witnessed the dust rings of microbursts. While at cruise alt I have had occasion to witness my ASI move from Vne to zero and back all in a matter of seconds. The takeoff or landing phase of flight is where the danger lies.

Roger Ritter said...

That 'spool-up' time is also why you'll see jets have speed brakes and/or spoilers deployed when landing. They have to keep the engines producing a bit more power to overcome that drag, and it's a lot quicker to retract the brakes/spoilers when more speed is needed than to wait for the engines to accelerate.

Mike said...

Stay. On. Ground.

mostly cajun said...

With light planes, several things become very important. First, your head has to be in the game to recognize and react. Second, it matters not how fast the engine responds if your rate of climb doesn't exceed the downward velocity. third, the burst is not a homogeneous phenomenon. The core may be pure 'down' but the periphery is a crazy mishmash of down, up, sideways...


SiGraybeard said...

I'm kinda "don't get me started on thunderstorms".

I design the hardware of the radar systems that do that predictive windshear analysis. (Windshear is what the effects of that microburst are usually called).

After that Delta 191 crash, the systems that the industry came up with would (unfortunately) only tell you when you were in a windshear/microburst event and that's pretty much too late. We've put a ton of money into researching how to predict that one is going to develop from far enough away to avoid it.

The other side doesn't get as much attention: the top of the thunderhead. We predict if a developing storm is safe to fly over. A quickly developing storm can throw hail at you, which can damage air transport sized planes, too. In the last few years, it has been discovered that thunderheads can blast gamma rays out of their top, too. I'd rather not sit in one of those, if possible.

At Davis-Montham Air Force Base there's a sign that says, "There's no reason to fly through a thunderstorm in peacetime". Just drop those last two words.

Old NFO said...

Even an overpowered prop plane (P-3) can't power out of a microburst... We lost over 6000 feet before it spit us out.

Quartermaster said...

If you escape one intact, be grateful. They have the ability to rip your AC apart.

J Van Stry said...

It's just not that the jet engines can take a longer time to spool up, it's also that the heavies are -heavy- and it takes time to accelerate all of that mass (inertia rules). Even a light airplane can find itself in trouble when suddenly there is hundred plus knot tailwind, and you find that your wing isn't flying anymore.
Or maybe now you have a couple hundred knot headwind, and you just exceed your airframe's design specifications.

I just avoid the angry clouds myself.