December 30, 1997
With the bout of deadly turbulence over the Pacific Ocean this week, aviation specialists and safety officials have been examining how to better prepare pilots and passengers. After a report by Betty Ann Bowser, Phil Ponce explores the issue with two experts.
ELIZABETH FARNSWORTH: Betty Ann Bowser begins our look at turbulence in the skies.
A RealAudio version of this segment is available.
December 12, 1997
The NTSB concludes its hearings into the TWA 800 crash.
December 11, 1997
A report on the danger of aging aircrafts.
November 18, 1997
The FBI concludes its investigation into TWA Flight 800.
August 19, 1997
What lessons can be learned from the crash of Valujet 592.
August 6, 1997
A report on the crash of a Korean airline passenger jet.
February 21, 1997:
The NTSB has determined the Boeing 737's rudder system is not as safe as once believed.
February 12, 1997:
A commission has come out with new recommendations to improve air safety.
November 13, 1996:
A report on the largest midair collision in history.
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Chaos at 33,000 feet.
BETTY ANN BOWSER: Dinner had just been served aboard United Flight 826 when suddenly, without warning, the plane seemed to fall from the sky. The Boeing 747 was a little over 1,000 miles East of Tokyo, heading for Honolulu, flying at about 33,000 feet when a passenger started taking these pictures. People were flung from their seats into the aisles. Food service trays, carts, and luggage were tossed about the cabin. Oxygen masks dangled from the overhead compartments. Most passengers said they were terrified.
PASSENGER: (speaking through interpreter) I went through the ceiling. I was panicked, and people were crying everywhere.
BETTY ANN BOWSER: What the 374 passengers had experienced was something called clear air turbulence. It's the leading cause of injuries to passengers and flight crews in non-fatal commercial plane accidents. Since 1981, two people have died in air turbulence incidents, one aboard Flight 826. The 32-year-old Japanese woman suffered a fatal head injury when her body was hurled against the ceiling of the plane. One hundred and ten other passengers were injured. Twelve of them are still hospitalized tonight.
United Airlines says the "fasten seatbelt" sign was on when the air turbulence started, but some of the passengers said it was not. Jim Hall, chairman of the National Transportation Safety Board, which will investigate the incident, said his agency doesn't know which report is correct yet.
JIM HALL, Chairman, NTSB: We have not independently been able to ascertain that. We will after interviews with the passengers and with the flight crew, which will be done shortly.
BETTY ANN BOWSER: Early analysis of the aircraft's flight data recorder by the NTSB this afternoon shows that the 747 initially rose suddenly, then plunged six seconds later about one hundred feet. The NTSB's investigation is ongoing. Meanwhile, industry officials are urging air passengers to keep their seatbelts fastened at all times when they are flying.
PHIL PONCE: For more on this story we're joined by Larry Cornman, a scientist at the National Center for Atmospheric Research in Boulder, Colorado, and John Nance, a pilot and author who serves as aviation analyst for ABC Television. Gentlemen, welcome to you both. Mr. Nance, a 100-foot fall, are you surprised that so much damage can be done by what seems to be not that great of a distance?
JOHN NANCE, Aviation Analyst: Not really, because it's not the fall that's important here. What is important is the amount of G-force that was exerted on the airplane both vertically up and down, and what it did to the passengers who were not strapped in and the crew and, for that matter, the carts in the aisle.
PHIL PONCE: Mr. Nance, how do pilots define severe turbulence?
JOHN NANCE: Severe turbulence is defined rather specifically because when you use that term, you trigger a lot of reactions; people not wanting to fly in that area and inspections on the airplane. Usually the one that sticks in my mind more than anything else is you can't read the instruments. You are bouncing so badly that you're just barely hanging onto the airplane, and you cannot read the instruments; that's severe.
PHIL PONCE: Mr. Cornman, from a scientific standpoint, how does one define severe turbulence?
LARRY CORNMAN, National Center for Atmospheric Research: Well, I think it's problematic in that its function is a type of aircraft you're in. So, for example, severe turbulence to a 737 might not be experiences of air turbulence, the 747. But certainly from a pilot's perspective, they cannot see, it controls very well, or handle the aircraft; that would certainly be considered severe turbulence.
Detecting turbulence and dealing with it.
PHIL PONCE: And, Mr. Cornman, why is it that this turbulence can't be more easily protected ahead of time?
LARRY CORNMAN: Very difficult problem. We really don't have sensors that allow us to see very well in clear air, there are certain type of sensors that are clearly under development, a device called a Lidar, which is a laser radar. But it's probably a few years off before we'll ever see any of these on commercial aircraft.
PHIL PONCE: Mr. Nance, what tools do pilots have right now to alert them that some turbulence is in the area?
JOHN NANCE: When you're dealing with clear air turbulence we have almost nothing, except our own analysis and experience of the weather reports and things, for instance, of where the tropopause is--that's the layer between the troposphere and the stratosphere--the temperature changes that we may run into and then upper air inclusion during the daytime, such as indications of other contrails or high clouds that might tell us that we're running into or out of a jet stream.
PHIL PONCE: And what are pilots trained to do when they encounter severe turbulence? Are there some standard procedures, or what exactly happens in the cockpit?
JOHN NANCE: Well, severe turbulence and clear air turbulence is an extreme rarity. It is very, very rare. This type of thing that we had two days ago with this United flight just doesn't happen very often, or we would have these type of reports all the time. Moderate turbulence is about as bad as it gets. And what we try to do is avoid any area like that. Sometimes you can't. The only tool you have available to you is to either change altitude, which is what we normally do. We are asking other flights, and we are asking the controller, is it smoother at 33, is it smoother at 31, whatever, and to sometimes vary the speed, but at high altitude, you don't have the option of slowing down a lot. So that really is--leaves you only the option of changing altitude, or changing course.
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.
PHIL PONCE: And, gentlemen, I thank you both for joining us.