Clear air turbulence explained.
PHIL PONCE: Mr. Cornman, what kind of--Mr. Nance talked about clear air turbulence. What other kinds of turbulence is there?
LARRY CORNMAN: Well, I think clear air turbulence is really a misnomer in a sense. I mean, it really refers to turbulence that can’t be seen by the eye, but actually causes of turbulence are due to things like the jet stream or frontal activity, or air flowing over mountains, or convection, and in most of the categories there can be clear air turbulence even associated with convection. So it’s somewhat a misnomer using the term clear air turbulence.
JOHN NANCE: Yes. Let me jump into that. I agree with you. We’ve got both the scientific and the pilot perspective here, but they are really complimentary. And what he’s saying is absolutely correct. There are mixtures of this. From the pilot point of view what I think, by the way, we’re dealing with in this, with this latest information about this incident, was an updraft, rather obviously a very, very substantial updraft, and one of the questions that NTSB is going to be looking at is: Was that in any way associated with convective activity from below that they might not have seen? Our radar won’t necessarily show that five or ten thousand feet down.
What happened over the Pacific?
PHIL PONCE: Mr. Cornman, based on what you know, what do you think was happening in that area when this happened?
LARRY CORNMAN: Well, I wouldn’t want to jump to conclusions yet, but what Mr. Nance said is possibly what occurred. It appeared there was large, massive thunderstorms to the Northeast, where the pilot was. He was trying to avoid that area perhaps and ran into a region where some thunderstorms were building very rapidly. Some satellite data that we’ve looked at indicates over a half-hour period the thunderstorms rose quite a large distance, so we’ve seen incidents of this type in the past where a pilot cannot see the thunderstorms either with their radar or visually. This incident occurred at night, so obviously the pilot didn’t have any visual clues. There may have been lightning in the area, but we don’t know that yet. But, clearly, if the radar, on-board radar was not pointed down, a pilot can’t see anything, and can blunder into something like this quite easily.
The power of turbulence.
PHIL PONCE: Mr. Nance, can turbulence break a plane apart?
JOHN NANCE: This type of turbulence outside of a major encounter with a thunderstorm, outside of a tornado encounter, outside of flying through a mountain wave at low altitude, the answer is, no, in almost no case. In other words, airplanes are designed to be very resilient, and this type of turbulence simply can’t overstress them beyond the design limits. But, again, all bets are off. If you fly in the middle of a thunderstorm or any of those other things I was talking about.
PHIL PONCE: And in the instance that you were talking about just a second ago as far as most cases, can turbulence cause a plane to crash?
JOHN NANCE: Turbulence can be the cause of loss of control. Back in the early 60's, when we were just learning to fly the big jets, there were several things called jet upset accidents, and it was basically a lack of ability, both of flight crew and at that time of the designers of the airplanes to understand what happens when you get a big jet aircraft into a high speed dive. I won’t go into the details, but basically we haven’t had that problem since the 60's, and the type of turbulence activity that can contribute to a crash is pretty rare and mostly associated with low altitude situations where you’re on approach. In other words, we get into the wind shear question.
The physics of safety.
PHIL PONCE: Mr. Cornman, you alluded to this earlier, and that has to do with the size of the plane from a scientific or from a vantage point of physics, the bigger the plane, the safer you are?
LARRY CORNMAN: Typically, that’s true. It’s a more stable platform. The smallest planes can lose control quite a bit easier, and say a 747, it’s rare that we see very severe upsets in the large planes, although certainly a plane that falls 100 feet in a very short amount of time can certainly do enough damage to people inside.
PHIL PONCE: And why is it, Mr. Cornman, that most of the injuries seem to take place towards the back of a plane?
LARRY CORNMAN: Well, that’s really an unknown question. There is some theory that the rear of the airplane--because of the--where the center of mass is, perhaps toward the front of the aircraft, has the tail of the aircraft whipping around more rapidly than the front, so people sitting in the back of the plane may experience greater forces, just as you might expect sitting on a teeter totter that’s unbalanced.
The need to buckle up.
PHIL PONCE: Mr. Nance, can one conclude that buckling up pretty much guarantees that one will not be injured in case there is turbulence?
JOHN NANCE: The word "guarantee" would bother me a little bit, but let me tell you that this is the quickest fix that we have. We have got to re-educate literally the flying population of this planet that when you’re sitting in a seat, that belt must be buckled at all times. Only when the light is out should you be able to get up and move out of that seat down the aisle to go to the bathroom or whatever else. But when you’re in the seat, whether the light is on or not, keep yourself buckled in. The only thing that that won’t prevent is being hit by somebody or something that has been thrust into the air above you in this type of rare encounter and comes down on you. But I’ve got to emphasize, this is an extreme rarity, even though it is a persistent problem.
What is on the horizon?
PHIL PONCE: And Mr. Cornman, you alluded to this earlier, but to what extent is there something more reliable in terms of a tool that’s on the horizon?
LARRY CORNMAN: Well, as part of our work with the FAA aviation research program there’s a number of different technologies that may be used, whether radar is either on board the aircraft or on the ground, or satellite information, or actually using the aircraft, itself, as a sensor, but really part of the key is to get better forecasts of turbulence so we don’t have planes going into areas that have severe turbulence. But I think it’ll be many years before we really have very accurate information based on forecasts that will allow us to prevent aircraft from having incidents just like this one.
PHIL PONCE: And, Mr. Nance, in the meantime, do you think pilots, practicing pilots such as yourselves, are going to be, what, making more of an effort to advise passengers, or being a little stronger in your warnings?
JOHN NANCE: We’ve been really strong up to now. I think we’re going to get even stronger at it. I think the whole airline industry has got to find a way to get people to understand, as I say, that you and your seat need to be intimately attached to each other at all times when you’re seated. That really is the key.
See the link below for the whole discussion.
http://www.pbs.org/newshour/bb/transpor ... 12-30.html
