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Aviation History
1974
1974 - 1901.PDF
^^ lite <> at Overseas Division's Heathrow base confirm, it takes in work from other airline companies—34 in all. The time has long since passed when aircraft were ritually dismembered every year and found, to nobody's amazement, to be in perfect order. Overseas Division operates a maintenance check cycle, administered by a Maintenance Review Board on which the airworthiness authority is represented. This Board decides, on the basis of defect histories, which components have to be inspected or removed during checks. These are sub-multiples of the "intermediate" check, which varies according to aircraft from l,200hr to l,600hr. The 747 took one year to reach l,500hr, the VC10 eight years, the 707 nearly 15 years. The old BOAC used to establish its maintenance schedules by eye and ear, but with the 747 a more scientific approach was essential. Aircraft of this size are such an enormous maintenance task that over-engineering could easily break their owners. A Maintenance System Guide was evolved, incorporating the experience of not only the Overseas Division but of Pan Am, TWA, United, American and Air Canada, among others, and the airworthiness authorities. (Similar maintenance guides have been evolved by British Airways. Air France, and Iran Air with the British, French and US airworthiness authorities.) On the 747 a third of the maintenance manhours involve components being changed "on condition"—say following borescope inspection—and 16 per cent are accounted for by changes of components whose failure rates have called for a "hard-time" (HT) life. The rest—53 per cent of the maintenance manhours on the 747—is devoted to condition monitoring. For each system and component condition monitoring is defined and refined by inputs from various sources— delays, pilot reports, hangar and workshop defects, in-flight engine shutdowns, flight data recorder, manufacturers' Service Bulletins, other airlines' defects, as reported in the FAA's Service Defect Reports, and plug and filter analysis. All defects from all sources are coded on to an IBM card and a computer investigates and prints out trends. The same data, by aircraft type and system, go into Sordid (the equivalent of European Division's React). Every problem comes up at the regular morning main tenance meeting at which a flight operations representative is present. If failure histories are worsening for a par ticular system or component an HT limit is called for. Overseas Division claim to have more experience than many airlines of condition-monitoring big turbofan engines, in its case the JT9D. Engine-condition monitoring (ECM) compares observed values with "signatures", and plots deviations. Data on nearly 300 installed engines reported in standard form and Telexed to London go into the com puter, which prints out trends. These are analysed each morning and problems are communicated to all station engineers. For example, immediate borescope inspections would be required after any turbine failure. The borescope is proving of great value to operators of the newer types of engine, there being no such method of checking JT3Ds or Conways. The trend in ECM is towards letting the computer analyse and present data to compare an engine with its shipmates rather than with the brochure —in other words, to show what the pilot sees. At London Heathrow, European Division's fleet, left, are at their morning gates, ready for the day's work. Their engineering base is a short tow away in the background. Right, the Overseas Division's engineering base lies a few minutes' walk away, also on the eastern boundary of the airport Last year JT9D engine condition monitoring, claims Overseas Division, prompted 25 per cent of all engine removals. Now being evaluated is a technique to print-out only the "exceedences" to cut down paperwork. The ulti mate objective is a computer actually in the aircraft dis playing engine misbehaviour in real time to the crew. All 747s are fitted with flight data recorders, or Airborne Integrated Data Systems (AIDS). Blocks of data from each engine regime—take-off, climb and cruise—are re duced to a single "snapshot" of exhaust-gas temperature and other parameters, and converted to standard conditions for comparison with brochure. The ultimate objective of engine condition monitoring is to change 100 per cent of engines at the home base. Engine shutdown rates Overseas Division engine shutdown rates are all well below the "accepted industry average" of 0-3/l,000hr. The JT9D-7s of the 747 fleet are running at 0-276; the Conways of the VC10 fleet at 0 138; the Conways of the 707-420 at 0-104 and the JT3Ds of the 707-320s at 0 076. The Overseas Division relies for its engine overhaul on the autonomous company British Airways Engine Overhaul Ltd (BEOL) at Treforest, near Cardiff. This facility's ex perience with Pratt & Whitney JT9D—which has been far from trouble-free—has resulted in what British Airways and P&W claim to be the lowest "float" of spare engines and modules in the airline industry, despite BEOL's support of a 747 activity with a peak utilisation of 14-7hr/day. Perhaps the sharpest contrast with European Division is in the Overseas Division's Flight Operations Centre, where the conventional chalked blackboards compare with the CRT displays and engineering staff of the short-haul operator. Each division has much to offer the other. The high tempo of the European operation has evolved a defect-manage ment system which could well become a common corner stone. The greater Overseas Division experience of the expensive, wide-bodied aircraft and their turbofan engines, and of common maintenance systems jointly evolved with other operators in association with manufacturer and air worthiness authorities, would seem to be another common cornerstone. The different defect-monitoring documents React and Sordid are both as advanced as any in the world, and appear to offer much common ground. A joint British Airways engineering department is not going to be put together overnight, and there will be many technical and human problems along the way. Patient negotiation with the Trades Unions has now got a study of integration off the ground, and conditions appear set fair for a joint management/union task force to examine selec ted areas for integration. The ultimate joint engineering effort should be one of the most professional in the airline business.
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