What flaws lead to such fatalities? And, how are engineers and other safety experts working to eliminate them?
In a study of 71 fatal airline accidents in the decade through 1977, the National Transportation Safety Board found pilot error in 63% of the cases and other human error in 43%. Bad weather was blamed in 45%, and mechanical failures in 27%. (The figures total in excess of 100% because, oftentimes, more than one factor was involved.)
That big jets have mechanical problems isn't surprising, if only because the planes are so complex. Just designing the new 767 is keeping more than 3,000 engineers and other workers busy, Boeing says.
Some problems with jets are so common as to be almost routine. An example: metal fatigue, which over time causes numerous structural cracks. To combat this problem, planes are designed to be "fail-safe"--that is, if one structure cracks and fails, others can carry the load, at least long enough for the plane to land. And inspections are designed to catch cracks even before the first structure fails.
Nevertheless, the system can fail--disastrously. As a Dan-Air 707 cargo jet came in from a landing at Lusaka, Zambia, in 1977, the starboard tail plane broke off and the aircraft fell, killing the crew of five. That accident touched off checks of 707s around the world, and cracks were found in the tail structures of 26 more of the Boeing planes. Airlines including U.S. carriers such as Pan Am, Trans World Airlines and American, are beefing up the tail structures on their 707s. Meanwhile, they are inspecting the 707 tails more often.
Another example of how the safety system can break down involves lightning. Jets are frequently struck by lightning, and they are built to absorb it safely. But in 1976, as an Iranian Air Force 747 jumbo jet was landing at Madrid, Spain, lighting hit the plane and evidently triggered a fuel-tank explosion. The left wing fell off, the plane crashed, and the crew died. Now, 747s around the world are being fixed to improve resistance to lighting.
Among the more difficult problems vexing airplane designers, however are the landing in general and tires in particular On most planes, inclusion of a second or redundant, landing-gear system simply isn't practical. As a result, engineers can't use the fail-safe design philosophy applied in most other parts of the plane.
As a substitute, engineers use a "safe-life" design strategy. Under this method, a landing gear is built tough enough to go through at least three times the takeoffs and landings that the plane normally would encounter in its life. Thus, the Boeing 737 can be expected to make 75,000 takeoffs and landings, but its landing gear is designed to handle at least 225,000.
The Chicago DC10 crash where the aircraft lost its port engine during take-off, flipped on its back and crashed killing everyone on board is a text-book example on how utterly feeble the fuselage is and how little protection it provides.
Tenerife 1977, two 747s collide on the runway
Pilots always get the blame. They're easy targets, they have virtually no clout to defend themselves, they're in control of machines whose design is dependent on complexity and that very complexity makes them virtually impossible to control in case of malfunction.
Mechanix Illustrated "Crashes CAN be harmless", June 1941 states: "Planes should be designed so they can take a good crash. Research departments can easily boast that they have developed instruments and gadgets that make crashes entirely avoidable. They can add these things to the pilots' compartment until the walls are cluttered up with them from top to bottom. They can evolve all manner of flapping, fluttering doo-dads that pop out of tails and wings and accomplish some purpose or other. For the most part, these things work quite well, but most of them need considerable attention from the pilot. When something unforeseen happens you can't blame the poor pilot for making a little error." And yet that's precisely what happens!
It also means airplanes are more expensive, thus increasing the cost of financing, of insurance (both institutions are closely linked and contribute to an enormous percentage of the overall cost of owning and operating an airplane). It also means higher employment, higher revenue, higher profits but someone has to pay for that: you! (and in some cases with your life)
DC-10 flips on its back, all perish.
It isn't practical to include a redundant landing-gear because it weighs too much. An aircraft whose fuselage contributes nothing to lift, with wings so small it has to be completely reconfigured before it can land or take-off, cannot be a viable economic work-horse if it weighs too much. Conversely, a lifting-body aircraft doesn't need a redundant landing gear because its take-off and landing speeds are low enough not to be a problem to the tires.