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National Geographic : 1977 Aug
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one thing that was unanimously mentioned by the nearly 1,000 pilots they interviewed, was the "lack of vertical flight-path guidance" during approach and landing. Vertical guidance. What is it? Suppose you're driving down a sloping highway on a foggy night. The road controls your angle of descent. Now imagine the road is gone, that you are flying instead of driving. What can tell you whether you are below, above, or on your approach path-something that gives you vertical guidance? At many U. S. air-carrier airports the In strument Landing System (pages 230-31) gives a pilot an electronic ramp to guide him toward the runway. By scanning his flight instruments, he knows he is on this ramp. Instrument Landing Systems, or ILS's, are installed on the approach ends of some 500 U. S. jetliner runways. The ILS electronic ramp does not guide the pilot-or the autopilot-all the way to the ground. At some point the pilot has to go "head up," looking for outside visual cues that will enable him to land. This transition period from instruments to outside visual references can last five or six seconds. What does the pilot need to see when he is transitioning from instruments to the real world? I have asked the experts this question from Los Angeles to London, and their re plies would fill a book. Basically, they dis agree; sometimes they fuss. Understand first that low-visibility ap proaches are few. They're like the very tip of the needle at the bottom of the haystack. Then what's the fuss? The NTSB has long recommended that the FAA forbid pilots to go below a predetermined "Decision Height" unless they can see the runway. The Air Line Pilots Association has made similar recommendations. The FAA maintains that its regulations setting Deci sion Heights for various aircraft and runway facilities are safe. Opinions Vary on Need to See But there are continuing questions even within the FAA. Dr. Stanley R. Mohler, chief of the Aeromedical Applications Division of the FAA's Office of Aviation Medicine, said he thinks a pilot, when transitioning, should see his "aiming point"-the point, roughly a thousand feet down the runway, where he wants to land. The FAA does not require this. Usually a pilot may "legally" continue his descent if he can see some of the approach lights that extend out from the end of many runways (page 233). He sees them before he sees the aiming point. How does this affect the safety of a bad weather electronic-ramp approach when the visibility on the runway can be as little as 1,200 feet? Retired Trans World Airlines Capt. Robert N. Buck, who flew many of these approaches It takes only a minute for the Turboclair system to clear fog. In the control room at Orly, a French Caravelle on final approach shows on the TV monitor. Other airports, in cluding fog-plagued Los Angeles International, are studying the system. 225
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