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Aviation History
1988
1988 - 3116.PDF
they serve on its network is to reduce brake wear. The restriction exists because full reverse (the system is total-flow reverse) induces heavy fluctuations in the stabiliser. Operational advice currently is that 80 per cent may be used in an emergency. Swissair's aircraft number six was delivered fitted with a modification which corrects the problem by setting a five-inch gap between the reverser doors to spill some flow centrally, and new upper doors angle the plumes further forward. Modifications to the earlier aircraft will have been completed by the end of November, and Swissair will not adopt reverse thrust as standard operating practice until the whole fleet is modified. The airline can see it becoming desirable at about that time for use on winter runways. Fod has not been a noticeable problem with reverse thrust use. One Fod lesson that the Fokker learned from its rear-engined DC-9 competitors was the need to have a ridged tyre to deflect water on wet runways so that it did not enter the engine intakes. Cabin environmental control demanded some remedial work. The temperature at the rear of the cabin was 7°C higher than at the front. Swissair said that it was because the rear galley air was being recirculated, so the intake was repositioned and the temperature difference is now acceptable at 2°C. "They don't use galleys in flight tests," remarks Hablutzel. Fokker gives a rather more complex description of what was done to sort the problem out, explaining that "Swissair's cabin layout is highly asymmetric, especially at the rear end, where the large left-hand galley has its own peculiarities". Variable restrictors have been introduced at points in the circulation system, so that air supply can be trimmed accurately between left and right, fore and aft, and this is now standard for Fokker 100 cabin environmental control. One thing which Swissair did in its galley was to dump hot air from the chiller unit heat exchanger through a hose to the under- floor area. The aircraft had shown (and occasionally still does show) a slight tendency to roll oscil lation, according to Swissair. It is not the kind you can feel, the airline says, just the kind you can see if you watch the wingtip against the horizon. Fokker explains that the effect was caused by "more backlash than specified in the aileron actuators", which it is combatting by modifying the actuator (already available at Swissair) and changing the autopilot software to enable it to handle As the last of Swissair's eight ordered Fokker 100s joins its fleet before the end of the year, so the last of its DC-9s departs Although the Fokker 100 has suffered some teething problems, Swissair insists that these have been unexceptional for a new aircraft. The airline, with obvious relief, says that nothing has surprised its engineers more backlash in the aileron channel (avail able early next year). One major modification which will have to be carried out on the earlier airframes (all those up to the ILFC and InterCanadian deliveries) is centre-fuselage strengthening. This need has shown itself only in the fatigue-test cell, which created centre- fuselage section fatigue cracks at 30,000 flight cycles. Fokker has requested that early aircraft return for modification before 8,000 cycles, equivalent to 2-3 years of operation. The cracks showed in the connecting strips between the upper skin panels and the frames to which the wing front and rear spars are attached. Modifications involve replacing the connecting strips by thicker ones using different material with a higher fractive toughness. This problem, Swissair says, is one of the few which showed itself after delivery; all others were known before and solutions were already being sought. Both the engineers and pilots at Swissair cannot praise the engines highly enough. Reliability is almost total, they say, and their quietness has won them friends. Both say they could do, ideally, with a little more power, but when asked whether Swissair was considering taking the option of the higher- rated Rolls-Royce Tay 650-15 (rather than the 620-15 which they ordered), the answer was a definite no, so they cannot be unhappy. Capt Ammann assesses the aircraft as "very much easier to fly than the DC-9. It has lower wing loading and much more direct control. The new cockpit means the pilot has less routine work to do, and so is free to monitor, manage, and look out." Peter Wolf, assistant to the chief engineer, has the final word: "We have not one prob lem that surprised us. We knew they were coming. On the whole we have been pleased." H 22 FLIGHT INTERNATIONAL, 29 October 1988
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