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Aviation History
1976
1976 - 0009.PDF
FUCHT International, w/e 3 January 1976 9 for the CAA to promulgate separately—both by Notam and on ATIS—the category of ILS glidepath and localiser so that the Tridents could operate on to that runway. Four runways are now available at London Heathrow for Trident Category 3 landings. 28R is preferred because the visibility is often better on the northern side of the field and because the best visual aids are located on that runway. In practice, British Airways has found that taxiing has mot been a problem. Most of the difficulties have affected aircraft turning off 28L. High-intensity green centreline lights are now used to lead the aircraft off the runway and it has been found, that an additional broken white line painted on the inside of the turn and starting 100ft before the change of direction is all that is needed to alert the crew. Significantly, taxiing for take-off in 100m RVR has produced no criticism, in contrast to the volume of suggestions following landings in 200m RVR. This part of the Trident 3 automatic-landing safety analysis shows the contribution to total accident risk of performance and missed-approach faults. Individual branches should be summed to arrive at the total probability PROBABILITY OF AN ACCIDENT X 10 7 0-7 PERFORMANCE 0 298 MISSED APPROACH 0-303 PITCH 0 078 MANUAL 0-27 AUTOMATIC 0-033 UNDERSHOOT 0-OO1 OVERRUN 001 RATE OF DESCENT 0 024 ATTITUOE 001 HITTING AN OBSTACLE 0-033 RUN OFF SIDE YAW ANGLE TOUCHING A HITTING AN OF RUNWAY 0 01 WING TIP OBSTACLE 0-1 0-1 001 education of Trident aircrew. Reduced visual segments and fog patches are available "to order" and various standard sequences are flown in the simulator as part of the six-monthly competence check. Regrettably, many exercises in the "box" have to involve failure drills, but Capt Ormonroyd is determined to avoid the impression that Category 3 approaches involve a series of equipment defects requiring a lightning response from the crew. Drills are concise and the cues simple—a tremendous improvement over the early days—and familiarity has created a high level of confidence in the system. This spring more attention will be paid to flying normal Cate gory 3 approaches using a variety of visual segments to emphasise the "real world" aspect of low visibility land ings. For a Category 2 approach, with 100ft decision height and 400m RVR, British Airways requires the captain to see and identify at least three centre-line approach lights and the runway. In Category 3a—12ft decision height and 200m RVR—the book requires that "several" centreline lights be visible (three are suggested) and that the aircraft should be within the touchdown zone. Should all visual cues subsequently be lost, the equipment will keep the aircraft straight while speed is reduced. Below 80kt the autopilot rudder channel is disconnected and the aircraft kept on the centreline using the guidance of the para- visual display (PVD) and ground-roll monitor (GRM). The ground-roll monitor, preset for all take-offs and landings, indicates groundspeed and distance remaining. For take off the full runway length is set, while for landing runway- length less 800m is used. "30 above" on the British Airways Trident 3 simulator at Heston (below). Several centreline lights are all that is needed for a favourable Category 3a decision. The paravisual display, shuttered as yet, is set in the coaming, just to the right of the captain's head. The centre coaming panel has the blue "rudder" lights illuminated at each end and the square indicator (third item from left of centre coaming panel) remains green, indicating full integrity for an automatic landing The Trident fleet now has the triplex fit, but when Shuttle plans were being finalised it was planned to keep the Trident Is duplex. Shuttle manager Capt R. Twomey held out for the triplex fit and the wisdom of his move is now apparent. The triplex version helps despatch relia bility and its engineering integrity is higher because it votes out the faulty element. The engineers, who deserve as much praise as anyone else concerned with the pro gramme, prefer the full triplex fit. At Glasgow a problem with control of the lighting should be resolved early this year; the runway will then be upgraded to Category 3. Edinburgh, soon to become the second Shuttle terminal, should go Category 3 before the end of this year. Abroad, however, there is often insufficient incentive for airfields to go for Category 3 if the national airline is unable to take advantage of the equipment. lata could play an important role by persuading its members to present uni fied low-visibility requirements to manufacturers and air field operators alike, British Airways BAC One-Elevens using a fail-passive autopilot are operating to Category 2 (100ft decision height and 400m RVR) and proving their worth at Tegel, where the cloudbase seems to he a permanent 105ft. Last Octo ber, 19 successive Category 2 approaches were flown, into Tegel; 62 such approaches were performed in the month. The One-Eleven equipment will not, however, be used for Category 3 operations. TriStar automatic landings are progressing well, having been set back a little by the tail scrape last May. Investiga tion of that mishap threw up two or three areas of risk which had not previously been identified. Modifications have been incorporated and the aircraft is now fully capable of Category 3b operations but is restricted to automatic landings in Category 1 weather until more experience has been gained. Category 2 clearance at 100ft decision height and 400m RVR is expected soon. Flight visited the British Airways Trident 3 simulator last month. The simulator has, of course, been vital to the Generally, the localiser is captured 8-10 n.m. from touch down. Autothrottle is used for the pod engines and the centre engine is set at about 11,000 r.p.m.; half flap and leading-edge slats are deployed. Approaching the glide- path, undercarriage is selected down and landing flap taken when passing about 1,500ft. The mode indicator shows a "full house" of lower captions, indicating that all subsystems are normal. Prime "Land" is selected at 1,000ft and missed-approach height set on the flight con troller. Below 700ft the triplex radio altimeters begin to indicate and at 500ft are positively checked by P3. Passing 300ft, Continued on page 34
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