Touchdown by Computer

British European Airways Trident Flight 343 approached London Airport one afternoon last week on a regular run from Paris. Captain Eric Poole sat in the cockpit, and the 80 passengers fastened their seat belts for the landing. The plane settled easily into the final approach and made a perfect touch down. But it was by no means a routine landing. As the plane taxied off the run way, Captain Poole got on the intercom to give his unsuspecting passengers a bit of a jolt: "Ladies and gentlemen," he said, "the approach to the runway and the touchdown have been made by automatic equipment on board." It was the first time that a jetliner with farepaying passengers aboard had landed by means of a computer.

The computer-operated landing system aboard the Trident is called the Autoflare, developed by Smith's Aircraft Instruments and Hawker Siddeley Aviation. Autoflare takes over within 150 ft. of the ground (see diagram). The plane is brought down the glide path toward the runway on radio beams from standard instrument landing equipment on the ground. From 150 ft. to 65 ft., twin computers aboard take control, directing the descent with information they have memorized and stored during the preceding 15 sec. At 65 ft., radio altimeters on board switch in. Now they signal the computers, which then bring the plane down to the proper landing point on the runway. The human pilot merely controls the plane's roll and yaw. Only at touchdown does he push a button on the steering column to disengage the automatic system.

Though pilots have made Autoflare test landings with their windows blacked out, the system at first will be used in regular commercial traffic only when the ceiling is at least 300 ft. As another safety precaution, the two computers are hooked up so that if they disagree or malfunction they will automatically cut off, enabling the human pilot to take charge. In the U.S., the only fully automatic landing system certified as airworthy by the Federal Aviation Agency is one developed by Boeing and the Bendix Corp., but it has not yet been used commercially. The British are understandably first. London Airport is fogged in at least a dozen full days each winter, and some days the pea soup is so thick that even a taxiing plane gets lost on the field.

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