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Aviation History
1961
1961 - 0252.PDF
254 FLIGHT, 24 February 1961 SYSTEM SUEVEY. One of Royston Instruments' CMM400 series flight recorders, the 400/7C for recording 270 parameters on six channels for eight hours. The tape cassette, in the right-hand unit, can be changed in seconds Flight-recorder Prospects T HE basic function of a flight recorder is to register in theaircraft, and preserve, a running record of significant flightdata so that, after an accident or incident, the record shallyield a history of events leading up to the critical moment. The desirability of such a device in transport aircraft has been officiallyrecognized for twenty years, but any legislation has been con- sistently baulked by shortcomings in equipment, either at thedesign or the manufacturing stage. Yet even the few and relatively unsophisticated recorders which are now being carried on pas-senger services have already proved their worth beyond question. Recorders of the calibre now available can undoubtedly avoid arepetition of the aeronautical detective epics which have been necessary to pin down the causes of some mysterious disasters.But that is not all a recorder can do. A whole new field, a new approach to maintenance and overhaul procedure, has beenopened up. With comparatively simple, compact and cheap equip- ment it is now possible to run a continuous analysis of aircraftbehaviour, component performance, serviceability and wear while still preserving the crash-recording facility. Prospects are dazzling,extending even into flight planning and traffic control; and there is a possibility that each individual aircraft could be calibratedby its recorder to allow flight-planning to much more precise limits than can at present be contemplated. Such prospects arebased on original work done by Royston Instruments Ltd, who have over the past four years developed a range of specializedelectronic tape recorders which offer the full flexibility in record- ing and analysis of tape systems. Lockheed Aircraft Serviceshave acquired the production licence for America and are now manufacturing and marketing the MIDAS system, as it is called. Recorders Made Mandatory Legislation requiring the carriageof flight recorders in passenger-carrying aircraft was first put into effect by the American CAB in 1957, after two abortive attemptsin 1941 and 1947. The requirement was that, by July 1958, all air-carrier aircraft of over 12,5001b gross weight operating at over25,000ft should carry a recorder for i.a.s., height, heading, vertical acceleration and elapsed time. The recorder should operate fromthe beginning of take-off to the end of the landing and the tape should be retained for 60 days after a flight. Various amendmentsand additions to this rule have since been made, including several delays to allow operators to survey the recorder market and takeadvantage of newer equipment and install it in an orderly and economical sequence. But by May this year there should besomething like full coverage of aircraft flying at 25,000ft or above. The Federal Aviation Agency's Technical Standard Order C51states that recorders should cover the "basic five" parameters and should conform to one of three types. Type 1 may be mountedanywhere in the aircraft, but must survive a crash impact of l,000g and l,100°C flame over half the container for 30min.Type 2 need only survive flame for 15min, but must not be installed near wing spars or fuel tanks. Type 3 must be ejectableand therefore need not survive flame. Arinc, the industry's radio authority, wrote two "characteristics," 541 and 542, which broadlyfollowed the FAA rules and types, but stipulated rack-mounted electronics and plug configurations. Arinc 542 covered recordersproducing mechanically inscribed material and 541 stipulated magnetic tape and about 60 channels in addition to the "basicfive." NASA meanwhile issued the VGH recorder specification which, as the initials imply, required speed, vertical accelerationand height recording. The VGH was mainly intended as a fatigue meter for B-47s and B-52s. Three recorders, generally meeting FAA Type 1 and Arinc 542specifications, were produced by Lockheed Aircraft Services, Waste King and General Mills (the last two are actually grain-milling concerns); and it is these which have been installed in jet transports. They generally inscribe continuous traces by indenta-tion of broad metal type which itself has the heat-resistant pro- perties. Minneapolis-Honeywell also proposed a complex flightrecorder, primarily for TCA, but this project has been modified. The "basic five" channels are limited, but even these haveproved useful on several occasions, notably the recent DC-8 colli- sion near New York when the recorder was recovered eventhough the DC-8 crashed into houses. The recorder was mounted near the forward passenger door in the main cabin and showedthat the aircraft had remained substantially on course until just before the Preston holding point. This it passed 3,700ft higherthan cleared and at some 358kt instead of the mandatory 180kt The tape indicated, too, that the aircraft was eight miles beyondPreston when the pilot radioed that he was approaching it. Recorders have also helped in less drastic incidents. It wassuspected, for instance, that a jet airliner leading-edge flap was shed because of excessive speed, but the tape denied this and adesign fault was found and cured. Search for the recorder is now one of the most immediate accident investigation procedures. If a record is ejected from the aircraft it must be provided witha means of flotation, a radio beacon and a dye marker. Some 72 par cent of the earth's surface is water.The FAA is enthusiastic about recorders. It wants, eventually, to achieve "across the board" coverage with an increased numberof channels recording engine and systems behaviour and more flight-path parameters. A project just completed is that of aspecial microphone to record crew conversation as well. Royston MIDAS In Britain, progress towards legislation hasbeen somewhat slower, although it was stated in Parliament last December that tenders were to be issued for development of crashrecorders for MoA. RAE Farnborough, as well as Royston Instru- ments Ltd, has been working on such equipment. It was theRoyston MIDAS project which first opened up the very wide horizons of the recorder as a maintenance tool. The latest CMM400 series of flight recorders cover sevenchannels on a 0.5in-wide tape moving at O.lin/sec. Each of six channels is time-multiplexed to record from 45 inputs once everysix seconds, making 270 channels in all. The seventh channel provides time data for controlling the de-multiplexer in the play-back equipment, for recording GMT and for aircraft identification, date and flight number. The recorders are produced in variousforms corresponding to Arinc 541 and FAA type 1 or 3 survival characteristics. Standard tape play-back equipment can be used,together with relatively simple equipment from which a variety of types of direct and computed investigation can be completed.Various scales of play-back equipment can be distributed along an airline's routes to allow anything from "quick-look" checking tocomprehensive statistical evaluation of the same tape record. There is no need to use the full potential of the tape immediately. Therecorders can cover various durations up to 160hr and the tape cassettes can be changed by unskilled labour in a matter of seconds. Royston have suggested that, for crash-recording purposes, itis the last hour of flying which really counts; and their ejectable unit might be a sub-station in the tail of the aircraft, recordingon a continuous one-hour loop of tape. The ejected unit would be a good deal smaller than the main unit used for maintenancerecording although it would still hold the full number of para- meters. It has been demonstrated that the tape can survive atleast six weeks' immersion in sea water without loss of information. Royston analysed civil airliner accidents over the past five yearsand determined 36 factors which would have indicated all the causes. The 36 factors accordingly represent the necessary mini-mum to analyse virtually any subsequent accident. They include the "basic five" and also engine power, fuel, control surface, flapand airbrake angles and the angles of their related tabs, cabin pressure and outside air temperature, autopilot servo position, ILSlocalizer and glide-slope signals and pilot's instrument indications. An additional 121 parameters for maintenance include indicationsof all system control positions and such factors as actuating motor voltages. The voltage required to operate a flap motor, for instancewill indicate the mechanical resistance in the system, showing a need for lubrication, inspection or change of unit. Repeated testoperations can be avoided and, Royston point out, 40 per cent of the operating cycles of a flap are done for test purposes and not inactual operation. Considerable wear could therefore be saved. In addition, maintenance recording provides a definite history ofwear and operation, which could allow overhaul life to be less conservatively rated. A final possibility is tape recording of acti-loperation of a complex electronic system in flight to allow rectifica- tion without further testing on the ground.
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