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Aviation History
1963
1963 - 1856.PDF
FLIGHT International, 17 October 1963 663 Fig S Most charts, like this one, use spot elevations alone. It is impossible for any reliable appreciation of the terrain to be obtained from them. (Reproduction approximately three-quarters original size) Terminal area charts These charts, intermediate between the .harts of instrument approach and the charts used en-route, have gradually come into being in order to supply adequate information on the entry and exit patterns introduced with increasing Air Traffic Control. In consequence, terrain problems have been given only token recognition: there are many such charts that show just a small random selection of spots (high points), thus inviting all kinds of false assumptions about the ground being low elsewhere (e.g., Fig 6). Contour envelopes would rationalize all this; and the effect on the appearance of the charts would be very similar to the above-mentioned instrument approach charts (Fig 4), except that to accord with the function of a terminal area chart the vertical spacing of the contour envelopes would of course be greater. Possibly on these terminal area charts the need for a proper portrayal of the terrain is greater than on any other type. These charts are in use during phases of flight where questions of climb or descent, or of an unexpected re-routeing by ATC, are predominant; and that such questions are at present habitually being tackled without having a handy picture of the terrain is really very remarkable. (It should here be emphasized that respons ibility for terrain clearance is not a part of ATC's terms of reference, so every climb, descent, or re-routeing has to be verified as to terrain by the pilot.) Radio-navigation charts (used en-route) The requirement here (Fig 7) is exactly the same as in the case of the terminal area charts, i.e., insteadof the usual token spots there ought to be appropriately spaced contour envelopes. Though this is nothing unreasonable, the suggestion that these charts should show terrain properly is often received with surprise. The surprise is due to the charts having a misleading name: as the name implies, they were originally conceived as fulfilling only the special function of radio navigation; and in order that the ovtrall requirements should be covered they were expected always to be supplementary to other charts or maps. This situation, however, has long since been modified in practice, and it is now true to say that for the en-route phase the radio- navigation chart is generally the only chart (or map) that is used. It therefore has an obligation to consider the whole navigation rather than only a part, and of the whole navigation one of the primary aspects is terrain. Critics will say that a requirement for one chart covering the whole navigation is all very well, but that since radio-navigation charts are already congested they cannot reasonably take the addition of anything not already on them. This argument is valid only if the whole of the information at present on them is more vital than terrain. It is a matter of priorities; and 1 suggest we "g 6 A terminal area chart (part of, reproduced here approximately three- yortersthesizeofthe coloured original), 'he few spots shown can do more harm than good, because they can encourage pilots to assume that elsewhere the i'ound is lower. Just how much lower? HDL 1LT. Jttafe Star MJ2TSA1 "^mmm^ i^sr^t J?' V £ \ 83 Vera mm V%A VH30C, «% rr i I* i ri«tMT %^ ft • LEGEND BEARINGS AKE MAGNETIC DISTANCES IN NAUTICAL MILES ELEVATIONS IN FEET OR B.T. LEVELS AS APPLICABLE. tSOGONALS fO* I9S9 MEAN ANNUAL CHANGE NIL >
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