How to Come in Blind

Except in dire emergencies the pilots of U.S. commercial jets are far too cautious to try blind landings with zero-zero visibility. When weather conditions at their target runways are worse than 200- 1/2 (200ft. ceiling, half-mile visibility), they are diverted to the nearest usable airport, which may be hundreds of miles away. The system is remarkably safe; during 1963 no fatal accident to a scheduled airline was caused by bad landing visibility. But passengers who were taken to Montreal instead of New York were seldom grateful, and airlines suffered financially. The Federal Aviation Agency figures that weather delays, diversions and cancellations cost $67 million last year. With air traffic increasing sharply, and supersonic airliners hopefully only a few years away, a better bad-weather landing system is a crying need. Last week a string of FAA officials told an Atlantic City meeting of the National Business Aircraft Association that the technical problems are practically licked.

Using the present Instrument Landing System (ILS), the pilot of a jetliner approaching a fog-shrouded airport hears the sound pattern of a "localizer" radio beam when he is approximately eight miles from the end of the runway. He follows the beam, and soon a radio beacon warns him by means of a sound signal in his earphones and a purple light flashing on his instrument panel that he is five miles from touchdown. A few seconds later, he picks up the "glide slope" beam, which controls a pair of pointers on the plane's instrument panel. By flying his plane to keep the pointers properly positioned, the pilot can keep to the center of the sloping beam. He sees nothing but fog ahead, and he knows that the runway is approaching at 150 m.p.h. A second beacon sounds its signal, to warn him when he has dropped to an altitude of 200 ft. At this point he must spot the brilliant runway lights. If he cannot see them or the runway markings, regulations require that he pull up and try again--or fly to another airport.

Guiding Cables. Below 200 ft. the glide slope beam of conventional ILS is not dependable because of ground interference and reflections from nearby buildings. In Britain, where fog is frequent and nasty, magnetic cables have been laid leading to the runways. Instruments enable a pilot to keep between the cables and glide down safely, even below 200 ft. But magnetic cables are not considered the final answer, even in Britain.

In the U.S., where dense, long-lasting ground fog is not nearly as common, the FAA is approaching blind-landing problems by two stages. The present system is Category I. Category II will permit properly equipped jetliners to land when the ceiling is 100 ft. and the visibility is one-quarter mile. The hardware for this technique has already been developed, says FAA. It consists chiefly of new antennas that give more dependable localizer and glide slope beams. One of them will soon be tested on an instrument landing runway at New York's La Guardia Airport.

To make sure of their altitude, Category II airplanes will probably carry radio altimeters, which are free of the uncertainties of barometric instruments. An airport that qualifies for Category II must install many "transmissometers" to measure local visibility along its two-mile runway, and it must be equipped with the best and brightest of runway and approach lights. With all this gear in working order, a Category II airport in the U.S. will seldom be forced to order incoming airplanes to go somewhere else. At New York's Kennedy International Airport, for instance, the ceiling is below the permitted 100 ft. on only about 16 hours per year.

Flare-Out & Glide. The FAA is not sure that Category III, true blind landing in which the pilot gets not a glimpse of the ground, will ever be popular in the U.S. where most pilots disapprove violently of giving up their critical control when bringing an aircraft to earth. But the British feel differently. At London Airport the ceiling is below 100 ft. for an average of twelve full days every year, and sometimes the fog is so thick that passengers cannot see the wing-roots from the cabin windows.

When supersonic transports become an actuality, the case for Category III is bound to improve. The SSTs cannot afford to circle above an airport waiting for fog to lift. Diverting them to other airports would be almost prohibitively costly. Many advocates of the SSTs believe that they cannot operate effectively without the capability of unrestricted blind landings.

The British have taken dead aim at Category III, though they know its difficulties only too well. The most serious problem is "flare-out," the flattening of an airplane's glide just before its wheels touch the runway. If flare-out is started too soon, the airplane may overshoot the runway. If it is too late, wheels hit the ground with a dangerous force. During a Category III landing, electronic instruments must judge the precise moment and control the flare-out maneuver through the autopilot.

After ten years of work a British government group called BLEU (Blind Landing Experimental Unit), has developed beam antennas, radio altimeters and other equipment that make completely blind landings comparatively easy and reasonably safe. British airplanes have made more than 10,000 fully automatic landings, and at last week's Atlantic City conference the FAA reported on a DC-7 prop-driven plane that it outfitted with British instruments with U.S. trimmings. Up to last summer, it had made 1,149 automatic landings at 47 different fields with only trifling errors.

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