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Aviation History
1956
1956 - 1590.PDF
748 FLIGHT, 9 November 1956 FUNCTIONAL EFFICIENCY —of Service and Civil. Aircraft: A Royal Aeronautical Society Discussion BOTH civil and Service aspects of the problem of the operatingreliability of aircraft were put forward during a discussionmeeting at the Royal Aeronautical Society in London on October 23. The two main contributions were by A.V-M. A. F.Hutton, C.B., C.B.E., D.F.C., Director-General of Engineering, Air Ministry, and Mr. Charles Abell, O.B.E., chief engineer ofB.O.A.C.; the chairman of the meeting was Mr. R. E. Hardingham, C.M.G., O.B.E., secretary and chief executive of the Air Registra-tion Board. A.V-M. Hutton's definition of an aircraft's functional efficiencywas "a measure of its technical ability to perform satisfactorily the task for which it was designed." The Operational Requirementof an aircraft, he said, included the required technical reliability; this was that an aircraft should be capable of completing 100 hours'flying with freedom from technical failure and the minimum of servicing. "This represents an ideal which so far we have neverattained and, in my opinion, it is doubtful if we ever shall." The minimum requirement for functional efficiency which mustbe met if the Service was fully to discharge its responsibility, A.V-M. Hutton submitted, was that the aircraft and its equipmentbe capable of undertaking a single operational sortie without incurring a technical defect. This minimum requirement wasnot met at present. For example, during last year's Fighter Com- mand exercise 283 sorties were abortive because of technicaldefects. This, on the basis of 12 aircraft per squadron and three sorties per aircraft per day, was equivalent to an operational lossof nearly eight squadrons for one day. Another method of expressing the problem was to comparethe number of defects with the hours flown. The overall picture for four types of operational aircraft showed a random defect rateof 0.9 defects per flying hour, and a total defect rate of 1.2 defects per flying hour (the difference being caused by defects foundduring scheduled servicing). The reasons for this state of affairs, the speaker suggested, fellinto five main groups. These were: (a) Failure inherent in swift technical advances; (b) failure of design to meet the specification;(c) failure of the specification to state the requirement; (d) fortuitous external factors; (e) bad servicing. Of these, the first two were the most important. Service aircraftneeded the application of the latest advances in technical research —even before all associated problems had been investigated—inorder to achieve operational superiority, but it seemed that the incidence of failure arising from this source could be reduced.The second reason listed included faulty design practice and unsatisfactory manufacturing processes; while an adequate fundof experience did exist, it appeared that this experience was not always available to those concerned with design. The incidence of failure in Service aircraft and the cost toService efficiency, the speaker summed up, was far higher than should be considered either reasonable or acceptable; the majorityof failures occurred at random during periods of accepted reli- ability; they occurred in lesser details but were no less costly forthat reason; and they were a problem common to all types of aircraft. Problems of Development The two main causes referred to were both basically develop-ment problems. In new designs much greater efforts should be made to obtain the maximum of experience in the shortest pos-sible time, and development should not be considered to have ceased when the aircraft C. of A. was granted. Only when newtypes reached the Service "in some numbers" could development be said really to begin. A.V-M. Hutton continued; "We in the Service have not beenentirely free from blame, for we tend to insist that we should only receive fully proven aircraft, not always realizing we have ourpart to play in development. I think we did realize some of our responsibilities in this matter about six years ago when we intro-duced a defect-recording system which is now in use throughout the Royal Air Force. A little while later we introduced intensiveflying trials of new aircraft, our object in both cases being to obtain accurate and statistical evidence of our experience. Unfortunatelyindustry on the whole has been slow to take advantage of this information, though very recently copies of our reports on inten-sive flight trials have been sent to the firms concerned." The most profitable field for saving time, the speaker con-cluded, was in the development period. The principal reason for slow development was the gap between the designer and theuser of the aircraft. "If we are to improve, this gap must be con- siderably narrowed and, better still, closed," The second main paper was by Mr. Charles Abell, who discussedfunctional efficiency from the airline point of view. The funda- mental criterion, he said, was the aircraft's revenue-earning poten-tial, and so the flying rate must be as high as possible. The time spent by aircraft on the ground could be classifiedunder five headings; scheduled transit time, scheduled terminal ground time, unscheduled ground time, maintenance, and service-able at base. Scheduled transit time at present normally amounted to 45 min.Manufacturers and refuelling companies had kept pace with the demand for higher fuelling rates, and aircraft were functionallyefficient in this context. Scheduled terminal ground time repre- sented servicing time at the overseas base and pre-flight and post-flight work at the home base. In the overseas element, which was by far the larger, there were two factors; the time found necessaryby experience to ensure that the return flight started punctually, and the fixing of the departure time at a convenient hour for thetravelling public. The first of these factors reflected functional efficiency, for this time allowance could be reduced if outwarddelays could be eliminated. Unscheduled ground time, Mr. Abell continued, was themeasure of unpunctuality. Not only did it affect the overseas turn-round time, but it was also one of the criteria by whichpassengers judged an airline's efficiency. Punctuality standards achieved by B.O.A.C. Constellations on the Kangaroo route toAustralia snowed that, over a six-month period, 95 per cent of all flights left London within one hour of schedule and 81 per centarrived at Sydney within the same tolerance. Homebound, some 87 per cent left Sydney within one hour, but only 55 per centarrived at London within this margin. Most delays arose either from weather or from technical troubles; in the case of B.O.A.C.Constellation aircraft, the latter was the prime cause. The power- plant created by far the greatest amount of trouble, accountingfor approximately 60 per cent of all the time lost due to technical causes. The same ratio applied to B.O.A.C. Stratocruisers, butthe figure for Argonauts rose to 80 per cent. » Efficiency of Maintenance " The amount of time required for maintenance was obviouslyclosely allied to functional efficiency, although the manner in which an airline went about the job also affected the situationmarkedly. Assuming that the maintenance activity were effi- ciently organized and performed, functional efficiency here wasrelated to (1) the reliability or longevity of components and struc- tural parts, (2) the ease with which these could be removed forrectification or overhaul, and (3) the ease with which these could be overhauled. These were the "three Rs" of reliability,removability and renewability. The fundamental responsibility for "design for maintenance"lay with the manufacturer and not the operator. An airline was only too keen to operate its aircraft to the best advantage, andundue distraction from this activity into the fields of engineering development could only be to the detriment of this primary interest.The need for close liaison between the manufacturer and the airline could not be stressed too strongly; "It has been myexperience that manufacturers differ widely in the interest they take in their products once they have sold them. I recall onelarge firm which has only recently seen to it that the reports of their by no means inconsiderable service department are chan-nelled back to the design teams! Undoubtedly, the accessory manufacturers are much more guilty in their failure to find outhow their products function in the hands of airlines, and I could mention several who apparently have no established channels ofcommunication, either with the airline or the aircraft manufac- turer to whom they are effectively subcontractors. . . . Obviously,a close link between manufacturer and operator helps both sides to do better business." The time allowance in the "serviceable at base" category waspartly conditioned by the route-operating pattern of the aircraft, partly by the fixing of departure times convenient for the public,and partly by the need for a high standard of departure punctuality. The continual battle towards functional efficiency, Mr. Abellconcluded, was the spearhead of good operations. This battle, if well-directed, kept an airline ahead of its competitors. Overallefficiency needed sound design and workshop practices, and punc- tual delivery. If thought had been given to reliability, removabi-lity and renewability, the aircraft would be popular with the airline engineers. Finally, if in addition it had passenger appeal and thusproduced high load factors, then the machine could be said to be truly efficient.
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