Science: Happy Landings

As they circled over Geneva, Switzerland, passengers in the French-built Caravelle jetliner had considerable cause for alarm. The plane’s landing gear was crippled, and the pilot was cautiously consuming excess fuel before he let down for a tricky emergency landing. Tanks almost empty, the Caravelle curved toward the field. There, just as its wheels touched down, the pilot popped a small drag parachute to check the plane’s speed. For anxious seconds the ship ran level, losing speed rapidly; then the right wingtip scraped the concrete; the plane veered slowly off the runway and stopped. Not a single passenger was injured.

The Caravelle’s drag chute, which almost surely prevented a ghastly crack-up at Geneva, is a simple safety device that most modern airplane designers and many pilots consider ridiculously oldfashioned. High-performance military planes use drag chutes to check their speed on touchdown, but all U.S. commercial jetliners prefer thrust reversal on their jet engines as an aid to braking. Like mechanical brakes, thrust reversers can be used as little or as much as required. In normal landings, commercial jets find thrust reversers far more efficient than drag chutes.

Sickening Skids. But there is still much to be said for the old-fashioned drag chute as an additional safety factor. In recent months, a series of crashes and near crashes has spelled out with deadly clarity the inherent difficulty of handling modern jetliners both in the air and on the ground. Complicated control and braking systems require complicated hydraulic systems, which have had a high incidence of trouble.

One of the worst jet crashes caused by hydraulic failure involved a DC-8 that lost its hydraulic pressure before landing at Denver on July 11. After a smooth landing, the pilot was forced to rely on a tricky emergency compressed-air system to work the wheel brakes. The brakes apparently locked, and four tires blew. Reverse thrust did not help, may actually have compounded the trouble. The great plane skidded off the runway, smashed a parked truck, crashed against a concrete shoulder and burst into flame. There have been other near disasters involving both DC-8s and 7075. and many of them have been caused by hydraulic failure. On any one of them, nervous passengers would have welcomed the added safety factor of a drag chute.

Drag chutes cannot prevent all landing accidents, and since they must be repacked after each use, they are not for routine use on commercial airplanes. But Theodore G. Linnert, head of the Air Line Pilots Association’s safety department, points out that when a pilot knows that he is heading for a dangerous landing because of something like hydraulic trouble, a drag chute would be an effective safety device. Thrust reversal used alone, in the absence of brakes, is difficult to apply evenly to multi-engine jets, may very well cause the dangerous skid it is meant to control. Popped out of its niche under the tail just at touchdown, a drag chute not only slows the plane but keeps it rolling straight, reducing the slewing effect of blown tires or uneven brakes and thrust reversers.

Triple Insurance. Drag parachutes are neither heavy nor expensive. On 6-52 heavy bombers, which weigh more than 175 tons fully loaded, they cost $830 per ship and weigh only 120 Ibs. The new Lockheed JetStar, a four-jet executive plane, carries as standard equipment a drag chute that weighs only 20 Ibs. Lockheed spokesmen believe that a JetStar chute has yet to be used, but they say bluntly: “The purpose is safety. It’s an insurance item for stopping. First you have the brakes, then thrust reversal, then the drag chute. It’s a good little thing to have around.”

Why do no commercial U.S. jetliners carry drag chutes? In questions of air safety, definitive answers are as scarce as antigravity screens, but several theories have been suggested. One is that the airline operators dislike such devices because their very presence suggests the possibility of trouble and scares potential passengers. Another argument is that the Federal Aviation Agency is not pushing drag chutes, and therefore the airlines and airplane manufacturers feel no urge to install them. The weight of a drag chute, after all, would eliminate a couple of passenger seats which, on the rare occasions when an airplane is chockfull, add to airline income.