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Aviation History
1963
1963 - 0013.PDF
FLIGHT International, 3 January 1963 200ft too low. Accepting the maker's legend that a spot height is the highest terrain in a general area might tempt the unwary into accepting the spot height just north—which lies within the 25-mile navigation lane—as the limiting factor in laying down a safety height of 10,100ft. Omission of the Mt Canigou spot height and its surrounding 9,000ft contour is certainly an error, and if this same error had been repeated to the west but within the 7,000ft contour, then the spot height of 8,110ft would have been the defin ing authority. For those who only allow 1,000ft terrain clearance, the answer might well be an accident. * * * It will be seen thus far that the denning authority for finalizing significant safety heights is spot heights rather than contours. Since no rules are laid down on the first two maps regarding these spot heights the only safe rule is to accept the highest point defined on the map. This means that for all practical purposes each sheet need only show its maximum spot height. This renders the rest of the maps, for terrain-clearance purposes, superfluous. The thought arises that if a map is divided into its natural squares of latitude and longitude, thus making referencing a simple prob lem, a select body of experts using every available source material should be able to produce an answer so exact and simple that the most inexperienced private pilot would be in no doubt as to his correct safety height. ONC-F-1 Contour values are written in on this map; and rules are clearly given regarding the reliance that may be placed on the spot heights. The limitations governing the maximum elevation within the defined areas state that where no doubt exists an over print in the centre of each square, e.g., 61 (6,100ft), indicates that this is the highest known terrain. If doubt exists then a minus sign is placed behind the figure warning the user that the experts, with all the source material they can muster, are estimating (ex perts' terminology for guessing). Where, in their opinion, the area is insufficiently surveyed no maximum elevation figure is printed and the user may make a guess on the basis of what information they have been able to provide. In other words, these cartographers have accepted a responsibility towards the users of their maps and indicate clearly what reliance may be placed on their work. The maps are further protected by a monthly revision service. Ob structions are printed on the charts but are not included when cal culating the maximum elevation figure, which only refers to terrain. Inspection of this map indicates that anyone operating in the Perpignan area should not descend lower than 97 (9,700ft) plus 2,000ft, giving a safety height of 11,700ft. The construction of a 40-mile navigation lane would reduce this to 11,200ft. The use of this safety lane assumes that the aircraft is equipped with aids that "Flight International" photograph 13 can guarantee its navigation within this lane in all weathers. Match ing aids must, of course, be available on the ground and the com pany operations manual should contain clear instructions on what course of action should be pursued should either the ground or airborne equipment fail. The rules which I set out below are a suggested approach to this problem. Maps serve a twofold purpose. The first is to provide ground- reading references; terrain clearance is of secondary importance since forward visibility gives an exact answer. The second func tion of maps is to answer the question: "How low may I fly, IFR, within the limits of my navigational capabilities ? The answer can only be the result of meticulous study of all available material by a body of dedicated and responsible people. Certainly a crowded flight deck in adverse weather conditions is hardly conducive to a study of this nature. The most convenient place to depict this information is on a radio facilities chart, providing this carries a weekly revision service and is reprinted monthly. Some measure of discipline must be exercised over the construction of obstacles on the ground, especially of 1,000ft TV masts, so that these are not in position until a week after this obstruction has appeared on the radio facility charts. The responsibility for producing this information must belong to the various Ministries of ICAO member States. If this cannot be arranged, then the British Ministry of Aviation must cover all areas used by British flag carriers. The suggested formula is that in areas where there are frequent and reliable track guides the airways pattern should have printed between each major reporting point the ten-mile Terrain Clearance Altitude giving 1,000ft clearance over all terrain and obstructions ten miles either side of the airway centre line. Adjacent to this should be printed the Minimum Safe Altitude which would give 2,000ft terrain clearance 30 miles either side of the centre line. Each square of latitude and longitude should have its maximum elevation printed in the exact centre (e.g., 61) and should be backed up by carefully selected high points (not spot heights) as an addi tional reminder that terrain or TV masts are in the vicinity. In areas where track guides are less frequent the Terrain Clearance Altitude should be based on a 40-mile lane and the Minimum Safe Altitude extended to cover 60 miles each side of track. This information should also be supplied for off-airway routings in common use. This system provides a built-in cross-reference, is practical and there should be no undue difficulty in implementing it im mediately. It also places the responsibility for public safety where it rightly belongs. It has always puzzled me that countries lay down airways without providing advice to users, such as terrain clearance altitudes, in case the aircraft inadvertently strays off the airway or does so as a result of an emergency. It is their own citi zens who are likely to suffer. It is also unrealistic to expect an executive or private pilot to set up an elaborate organization to cover himself for occasional flights. I am certain that if the Minis try set up such a study group each airline would gladly contribute staff in order to obtain these answers before next season. After all, we are all affected, and the present selection of maps would appear to be inadequate. It is a sobering thought that, despite the very considerable pub licity given to the Mt Canigou accident, one still hears unpres- surized aircraft requesting IFR clearance between Toulouse and Perpignan at flight level 75. A study of the table overleaf clearly shows that when navigating with the assistance of only one ADF, the 40-mile Minimum Safe Altitude must apply, i.e., 12,500ft. Suggested Rules for Increasing Safety (1) Radio facility charts as described above should be produced and their use made mandatory. (2) Every captain should have his own flight guide and topograph ical maps for all the regions for which he holds a clearance. (3) Both the charts and the maps should carry a weekly revision service. The pilot himself should carry out his own amendments as this provides self-briefing on changes affecting his area of opera tions. (4) Selected VOR stations should broadcast the actual weather for six adjacent airfields plus the winds for each 5,000ft level and these winds should be corrected as frequently as is practical. For example, Toulouse would give actuals for Tarbes, Limoges, Men- tellimar, Perpignan, Barcelona and Toulouse, plus its own winds aloft. [Continued overleaf
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