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Aviation History
1964
1964 - 1286.PDF
'21 FLIGHT Piper Cherokee Comanche ISO accurate approach in conditions of 500ft ceiling and half-mile visibility, or possibly even less. Nevertheless, equipment with a manually tuned VOR which cannot be used independently of the communications is usable for en route navigation, but is quite unsuitable for let-down procedure. Fields without their own beacon can often be found by flying on a back-bearing from nearby beacons, and en route fixes can be obtained by cross-bearings. So fascinating is VOR that a pilot may imagine that it absolves him from the responsibility of knowing exactly where he is. On the contrary, the idea is to make flying more accurate, not less so. It is interesting to note the reactions of different pilots when their VOR suddenly ceases to function, which does happen every now and then. Pilot Training VOR navigation looks easy on paper, but in fact demands a good deal of practice and considerable care. Expert instruction is not always available at clubs where this type of aircraft and equipment are for hire. A sound knowledge of existing ground services, location of beacons, morse code, and of radio facilities guides is essential if full use is to be made of VOR. Its occasional and dilatory use for navigation gives a rather false impression of simplicity and can lead to trouble. Limitations The VHF radio fitted in this case still has lOOkc/s spacing, which no longer gives access to all airfields or terminal zones within appropriate local conditions of time and minima. Study of a radio facilities chart will show that at the present time VOR coverage in Britain is far from complete. In fact, north of Daventry or much beyond the Channel coasts it is inadequate for point-to-point navigation in a private aircraft. (This aircraft is fitted with an excellent crystal-tuned VOR receiver, but some of the so- called "Mickey Mouse" varieties are difficult to tune, insensitive and far from foolproof.) With the temptation to use such equipment to its limits serious difficulties can arise in the event of component failure, because there is no stand-by. But for a pleasure aircraft with radio equip- ment at a realistic price this example will be hard to beat. The sensible pilot with instrument training and a sound knowledge of his apparatus can take advantage of the facilities, which are pri- marily laid out for airline navigation. So long as he is content to observe its limitations this will normally be all he ever needs. (4) Comanche 250 360-channel VHF with 50kc/s spacing, stand-by 190-channel VHF, VOR/ILS Loc, ADF and marker receiver; full blind-flying panel. This is quite a sophisticated complement of equipment, and one which will enable a pilot to use any aerodrome he is permitted to enter. The stand-by VHF is a safeguard against failure and has other uses as well, for instance, in facilitating rapid changes of frequency. The VOR receiver incorporates an ILS localizer, which enables one to follow the centre line beam almost to touch-down from ten or more miles away at most major airports. Tne markers give critical distances from touch-down as well as certain en route fixes. The ADF is in fact an older device than VOR, but it has several outstanding advantages at the present time. It is extremely robust, Provides a constant indication of the direction of the station, gives almost complete coverage in the UK and Europe and operates at any altitude. An ADF let-down, once the peculiar technique isned > can be surprisingly accurate down to minima of about It is not so easy to interpret as VOR, is sensitive to inter- erence and more difficult to tune, but it will remain in widespreadU!ie for m any years. ADF is certainly not to be despised though it requires care and skill. fne possession of the two radio navigation aids means that spot- checks of precise position can be made, flying for instance along a VOR radial and up to a cross-bearing from an NDB pre-computed for some specified point. More airfields have short-range NDB locators than 1LS or VOR, though their range, certainly in Britain, is limited to a score or so miles. Pilot Training The effective use of radio equipment such as this demands an almost professional standard from the pilot, with constant practical experience of flight planning, en route navigation and radio procedure, familiarity with terminal control and a good deal more. Manipulation of VOR and ADF bearing information requires a fair amount of mental agility. ILS is by no means so easy to use as it would appear on paper. This panel brings a pilot unequivocally on the side of instrument flying, even on quite short, simple journeys in good visibility. He can often obtain special VFR clearances in conditions well below VMC minima, and he can safely make an approach and landing when nothing less well-equipped could fly. Limitations Good as it is, this equipment is not all to ARB Class 1 standard and hence not accepted for an IFR flight plan which, incidentally, also requires an instrument rated pilot to file it. Otherwise, the limitations imposed by the panel itself are very few, and most really experienced pilots would be happy to take this Comanche anywhere in the world. Yet, for entry or exit at a terminal zone in less than the rather generous VMC minima, the special VFR clearance demands that the pilot fly clear of all cloud and in sight of the ground, often forcing him either to fly in really marginal conditions or to abandon a flight which he could other- wise make quite effectively IMC, though not fully IFR. Height restrictions implicit in special VFR may force the pilot to fly low over a populated area—London (Heathrow) may specify 900ft— or over the sea. Evidently full use cannot be made of the facilities commanded by this panel without the fullest and latest information about them. Possession of (and familiarity with) a constantly up-dated guide geared to off-airways as well as airways operation, is essential for this kind of flying. A glance at one section of a Jeppesen chart, illustrated overleaf, gives some idea of the facilities available and also the complexities of modern radio navigation. (5) Beech Queen Air Two 360-channel VHF com, two VOR/ILS, one of them with glideslope receiver, ADF and marker receiver, all Class 1. This particular aircraft has in addition HF com, weather radar and autopilot—more than IFR. With its comprehensive equipment, including de-icing, this twin-engined aircraft is intended to be flown by a professional pilot virtually anywhere on the same terms as a scheduled airliner. The equipment is of high performance and capacity, and very reliable, with duplication of both VHF and VOR to provide added flexibility and failure survival. A Class 1 ADF of this category is easier to tune than the cheaper sets, and provides considerably greater protection against faulty tuning. Pilot Training Full use of an aircraft of this standard essentially calls for an instrument rating, which is not too easily acquired and has to be renewed every year. A few private pilots have found an instrument rating worthwhile for the fullest use of their aircraft in business, though most full-IFR twins of this type will, of course, be flown by professional pilots. For the non-instrument-rated pilot, however experienced he may be, this aircraft offers little advantage over the previous one, because he cannot file an IFR flight plan and is himself more restricted than the aircraft. Limitations The only limitations of this class of aircraft are those
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