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Clouds Clouds can deceive pilots as to what is ground and what is sky.
Reading the Wreckage
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NOVA: What sort of wreckage pattern might you expect from a crash in mountainous territory?

KING: Flying into rock most of the energy is absorbed in destroying the aircraft, breaking the aircraft into lots of small pieces. That's why finding crashed aircraft in mountainous terrain can be extremely difficult. There isn't a big scar across the surface that one finds in open fields.

The wreckage trail can virtually be reversed, in that if the mountain continues to descend below the point of the impact, the wreckage will tend to fall backwards in the direction from whence it came, rather than distribute itself in a forward fashion from the aircraft's momentum.

NOVA: What sort of things would you be looking for to tell you whether or not there had been a fire either in the air or on the ground?

KING: Fire is one of the enemies of accident investigation in that it consumes evidence. Major ground fires make interpretation of the scene and wreckage that much more difficult. Airborne fire has certain characteristics that stand out from ground fire under some circumstances, so if there has been fire in the air we do stand a chance of identifying that from examining the detailed fire signature in the wreckage.

Reading the wreckage Members of the Argentine military team investigate the Stardust crash site.

NOVA: What advantages do you have now in investigating an accident that you wouldn't have had 40 or 50 years ago?

KING: First and foremost we have cockpit voice recorders and flight data recorders, certainly for the major public aircraft types. The cockpit voice recorder gives us information about what was going on on the flight deck. We don't have vision, we only have sounds, of course, so there is some interpretation, but it allows us to tune into crew conversations and air-traffic exchanges.

The flight data recorder records various parameters about the flight, such as the height of the aircraft and the speed at which it's traveling against a base of time. The most modern recorders also look at aircraft systems, giving us data on how the engines, the hydraulic systems, and the electrical systems are working. It can tell us an awful lot about what's going on inside the aircraft mechanically and electrically as well as give us the flight path of the airplane.

Together these so-called "black boxes"—actually they are typically bright orange—go a long long way to telling us what has happened. The recording medium on most is a fairly common recording tape, Mylar tape, which is encased in a solid outer case to protect it against impact damage. Inside each box is an insulation material as well to protect the tape against ground fire for a limited time.

NOVA: What does the data stored in the tapes enable you to do?

KING: After we've downloaded information from the flight data recorder, for instance, we can present it graphically for people to study and analyze. We can also create a visualization. We can present the data on a copied instrument display, that is, in a manner similar to the way the crew would have been able to observe it, assuming the aircraft's instruments were working properly. We can also do simulations that enable us to view the aircraft in its maneuvers from some outside point. What this brings to the analysis is the ability to make things move in real time. Sometimes when analyzing data on detailed traces, time is the element that one tends to lose at the speed with which things are developing.

Andes With radio beacons and inertial navigation systems, flight navigation over the Andes is much safer today than in 1947.
NOVA: How would you compare navigation today with that of 50 years ago?

KING: Navigating Stardust 50 years ago would have depended on looking out of the window and using the forecasted winds to predict speed and drift angles across the ground. In broad terms, aircraft today that are travelling long distances like Stardust was would be using inertial navigation systems, which are updated by radio beacons when they're available on the ground. These systems have multiple redundancies and are very reliable.

NOVA: Can you imagine an aircraft today vanishing for 53 years?

KING: That would be very unlikely to occur today. We have massively improved communication and navigation capability. It would be extremely unusual these days for an aircraft to disappear without controllers having an extremely accurate idea of where it had last been located.

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