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Aviation History
1961
1961 - 1637.PDF
FLIGHT, 9 November 1961 reverse sense. The pilots immediately asked themselves why, in several years of operation, this fault had never occurred before. The ground staff told them that it had in fact happened several times, but had always been spotted by the inspectors. It was then asked why the inspectors had not drawn the attention of the manu- facturers to this blatant candidate for Murphy's Law and the reply was: "It would make us look rather fools, wouldn't it?" During the subsequent discussion of Capt Bressey's contribution it was clear from many comments that automatic approach coup- lers are still used relatively infrequently. A BEA Comet 4B captain described an approach technique developed by his airline which in- volved the regular use of approach couplers. Once the equipment was used and the snags systematically rectified the equipment worked well. A BOAC Comet captain then wondered how BEA had had their approach coupler cleared for operation when identical equip- ment in BOAC Comets was wired off and placarded "not to be used." Other speakers noted that their approach couplers were not to be used below 1,500ft, yet another said that radar sequencing procedures at London Heathrow made it impossible to engage the coupler in time to make an automatic approach. These and many more comments all illustrated Capt Bressey's point that teething troubles destroyed pilots' confidence in auto- matic equipment. It was obvious that pilots would never be recon- ciled to automatic landing, which involved much greater reliance on equipment, unless it worked better than approach couplers even in the early introductory stages. But it was also clear that equipment which got a bad name and was shunned early in its life could be made to work very successfully if the pilots consistently used it, reported snags and allowed the engineers to eliminate them systematically. Willingness to co-operate whole-heartedly in the difficult early stages was not so evident as the inclination to ignore new equipment after the first few unhappy experiences. Visual Simulators The operation and usefulness of the GPS Terravision visual attachment for simulators were explained by Mr Douglas Wilson, head of the simulator division of General Precision Systems. (Terravision was described in Flight for January 20, 1966). Mr Wilson noted that pilots might get their first visual experience of a poor-weather landing in a new airliner with a load of passengers behind them because marginal weather was hard to find for train- ing. Minima were increasing rather than decreasing at the moment and pilots" ability was likely to decrease with the introduction of automatic landing. The visual simulator could help,. Mr Wilson showed a film illustrating the view obtained during various kinds of simulated ceiling, visiblity and lighting conditions ending with some dramatic low flying. The visual attachment, he said, was in production and had been ordered for the RAF and BEA. One visual unit could be shared between several simulators. Future developments included use of colour TV, better methods of reducing visibility and provision of a limited circling capability. Decca for Landing Guidance A description of a new application of Decca Navigator to landing guidance was given by Mr Claud Powell of Decca Navigator Co. The system is to some extent based on the small chains used for survey work and employs two stations, master and slave, disposed symmetrically beside the runway. They would, said the speaker, produce a hyperbolic pattern [see illustration] with the character- istics that, from the maximum range of eight miles to about two miles, the lanes would provide angular information and at shorter ranges would give displacement information. The centreline would be straight and cover the whole runway and both its approaches. Sensitivity would be 0.75ft on the runway and eight feet at eight miles, giving an overall accuracy of two or three times these values. Transmission of a second pattern in phase on the centreline only would resolve lane ambiguity, but ILS is envisaged for positioning the aircraft initially on the correct lane. The transmitters would be mounted in vans and the aerials would be 25ft high. Transmission frequencies would be in the NDB Right, the Decca pattern for centreline guidance. Below, full pattern with ranging, using four transmitters 741 The model gantry and television camera assembly of the General Precision Systems' visual attachment band and "site consciousness" would be low. Ability to overcome static would depend on transmitter power, but reasonable powers should prove effective. The short ranges involved would greatly alleviate such problems. An airborne receiver might occupy less than J ATR case. The beacons could be airportable. A range pattern could be superimposed on the azimuth pattern either by the addition of two further beacons or of a further master. BEA Plans Speaking from what was possibly the mid-point between the pilot and the designer, Capt F. Ormonroyd, BEA's flight technical superintendent, outlined the stages of equipment planned for the Trident and the benefits the airline hoped to obtain. First stage for the Trident was autoflare, requiring no special ground equipment, but providing experience of automation. The autopilot would be duplex in pitch and roll and duplex in yaw for autostabilization only. Also provided would be a flight director working together with the autopilot, and PVD shuttered until used in case of a failure; duplex throttle control; auto-oyershoot using the approach-speed lock, except after throttle-closing had begun during flare-out; three radio altimeters and flare computers serving autopilots and flight system; two ILS receivers, one for the autopilot and the other for visual monitoring; and attitude- hold phase for transition from glide-slope to radio altimeters. The first Tridents would be so fitted, but certification might not be complete. The second stage was for gaining experience in good weather. It would involve a third ILS localizer and azimuth computer to give independent guidance to each autopilot channel, and a kick-off drift system in the duplex yaw channel. PVD would indicate failure and provide manual guidance. If suitable ILS was not available, normal ILS could be used in good conditions on 300ft- wide runways, such as at London Heathrow. [Contd overleaf \ MASTER. .SLAVE
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