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Aviation History
1960
1960 - 1404.PDF
Accent on the Unexpected ... Primary factors which govern the location of engines at routestations are: the frequency of aircraft calls, the discomfort of passengers delayed in the tropics, and the distance from base ofa terminal such as Sydney. In relating the demand for replace- ment engines to the frequency of aircraft calls, BOAC wereprobably the first airline to apply the queueing theory to their spares planning. A simple everyday example of this theory inpractice can be seen in Piccadilly Circus Underground station. Facilities of a certain kind are provided in two exit subways,Regent Street North and the Haymarket. The frequency of calls is probably greater at the first and the turn-round timelonger at the second. The London Transport planners appear to have made a remarkably accurate assessment of demand forthe Regent Street facility, but they have not been so successful on the Haymarket side, where a queue may sometimes be observed.BOAC have not however extended their application of the queueing theory beyond engines, and it has been left to TWA,enthusiastic supporters of BOAC's idea (see Flight, October 30, 1959), to cover similarly the complete range of rotable components. Lifed Components. The initial quantities of the other lifedcomponents, 400-500 in number, are provisioned by a formula which is related to the maintenance check and overhaul cycles,and includes a casualty allowance to cover route positionings. Although barely 4 per cent of the 25,000 items in the Cometsupport programme are in the repairable category, these 1,000 items account for 70 per cent of the cost. Computer provisioningmay therefore be inevitable, in order to achieve the degree of accuracy that is essential in this expensive business. Data Processing. Neither corporation has so far adoptedATA 200 or any other data-processing procedure in their parts systems, although BEA are preparing to introduce a punched-card system (probably during this corning autumn) which will cover 130,000 live items, including equipment and raw materials.BOAC have similar plans in hand, and both corporations are probably ahead of nearly all their suppliers in this respect. Hopesare expressed that a combined start can be made by suppliers and operators together, with the D.H.121 and the VC10. Supply. Once the initial float is in position—which shouldbe before final delivery of the new fleet—stock replenishment of repairable components will rarely be necessary, assuming nointerim life changes, as (apart from the occasional scrap) these units will be overhauled to full life each time. It is of the utmostimportance to commercial operators that stocks of consumable parts are replenished by the manufacturers at a guaranteed rate.Bin levels are related to operator's consumption and to the replenishment rate from the manufacturer. This is comparableto the cistern in a house; cisterns would have to be considerably larger if immediate replenishment was not guaranteed. The cor-porations would like to see their buffer stocks of consumable parts set at a level based on one month's average consumption. That FLIGHT, 19 Align- 1950 "Rolls-Royce still have no betters at parts supply." The buildi ••> fr which they serve their customers at London Airport m some of the manufacturers experience difficulty in main iin;an adequate rate of replenishment is proved by the neces^ i;y fn§ the corporations to raise their buffer levels for certain [•>•.as much as six to nine months' stock. ° Crash Action. A thorny problem to all parts planners Js crash—excluding, of course, the total write-off, where ther": is nproblem. The initial support programme does not allow for an aircraft being broken or dented, although this may occur in anvairline. It is the manufacturer, then, who has to provide the crash support, the cost of which would as a rule be covered eventuallyby insurance. The operators are naturally anxious to have a broken aircraft returned to service as quickly as possible, and no effortis spared by British manufacturers to achieve this purpose. I nspite of the severe restrictions imposed by finance, Bristol, de Havilland and Vickers provision substantial crash-inventories ofmajor items in anticipation of breakage. The Americans have an advantage in their capacity to meet at short notice emergencydemands which have not been forseen. Shortages do unfortunately cause hold-ups to repair programmes and, rather surprisinglysometimes turn out to be minor items such as special bolts. Common Pool. An aid to economy in the support programmeis the establishment of a co-operative pool to share insurance positionings on common parts. It is plainly foolish for two ormore operators to position identical components at the same station on a "just-in-case" basis. Most operators and manufac-turers nowadays appreciate the futility of such extravagence, and both corporations co-operate actively with other operators whoshare their routes and have common equipment; this is done through the European Purchasing Committee and similar associa-tions. The big Boeings provide the incentive, as well as the opportunity, for pooling resources in a big way, and there wouldappear to be a good case for a concerted application of the queueing theory at the stations served by the several operatorsof this aircraft. Similar economics are being achieved with the Comet and the Viscount. One day, perhaps, the trend will developinto a world-wide chain of independent distributors carrying such slogans as "British aircraft parts and service." It is, however.rather surprising that two such close neighbours as the corpora- tions appear to prefer to "gang their ain gait" in their respectiveparts support of the Comet. Conclusion. Two factors predominate, either or both of whichcan play havoc with a support programme. The first is over- estimating component reliability; this disrupts the overhaulprogramme, owing to the inevitable shortages which follow the inability of manufacturers to satisfy increased float requirementsat short notice. The second is the failure of many manufacturers to adhere to their own published lead-times, and their quotedpromises for the delivery of parts. One manufacturer has been heard to claim that his delivery "promises" were only intendedas "rough guides" to his customers, and in some instances the customer has even found it politic to make a point of saying"thank-you" to his suppliers for promises kept! Some manufacturers are making an encouraging attempt toprovide off-the-shelf and over-the-counter service for both new and reconditioned parts. Rolls-Royce still have no betters atparts supply, and de Havilland give good support with parts of their own manufacture for the Comet 4B, from the store whichthey have established in one of BEA's hangars at London Airport; but the ancillary manufacturers are, as a group, regrettablyinadequate in their parts support. Dunlop can be named as one of the few who try to anticipate their customers' requiremenrs. Material—fuel, food and parts—is the life-blood of thecommercial aircraft, which is only of value to its operator if it is complete in all respects. Makeshift is no longer of any usein materials supply. Complete understanding between the airline and the manufacturers at all levels is essential to an otherwisecomprehensive support programme which, lacking an accurate estimate of reliability of components, and a reliable estimate ofavailability of parts, may still come apart in the operator's hands. "It is rather surprising that . . .the corporations prefer to 'gang their ain g"H' '" their respective parts &P; port of the Comet.' This is the new east bhek at BEA's engineering base
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