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Aviation History
1961
1961 - 0177.PDF
IGHT, 10 February 1961 177 ISHT SYSTEM SURVEY Trident Autoflare Equipment 1 :;E equipment and operating sequence of the autoflare systeminitially to be put into service in the de Havilland Trident are described in an article by J. W. Wilson, one of the company'soperations engineers, in the de Havilland Gazette this month. Present autopilot-coupled approaches cannot be continued muchbelow 200ft, partly because of the run-away characteristics of single-channel autopilots and partly because the normal ILSglide-slope signals become unacceptable below about 150ft. The automatic flare-out landing is made following a normal ILS-coupled approach with automatic throttle control. At about 150ft on a 24 to 3° glide-slope, the aircraft is approximately 3,000ftfrom the glide-slope transmitter and, therefore, some distance short of the runway or its level undershoot area. Glide-slopeguidance must be disconnected, but radio altimeter height-guid- ance cannot yet be relied upon, because undulating ground orobstructions might interfere with height measurement. The aircraft would be over suitable ground at about 70ft; andthe hiatus between glide-slope and altimeter guidance, lasting a few seconds, would be covered by holding a pitch attitudeaveraged during the preceding approach phase. This sequence is clearly shown in the diagram reproduced below. Below 70ftpitch attitude is controlled by the autopilot, using height and rate-of-change of height signals derived from the radio altimeters,and power is automatically reduced during the flare-out. It remains for the pilot to control yaw and roll, and he must beable to see sufficiently well to line-up the aircraft with the runway and to kick-off drift. The operations he has to perform are shownin the diagram and table. As well as controlling yaw and roll, he must monitor the automatics to see that they are operatingcorrectly, and must be ready to take over in the event of a failure. Mr Wilson points out that the successful exploitation of auto-matic flare-out may in reality depend on the confidence of the crew in the equipment, and upon their ability to monitor the automaticseffectively. No very great reduction in weather minima is expected, because the pilot must still be able to see the runway. The Trident equipped for automatic flare-out will not initiallyhave the full triplex Smiths SEP. 5 autopilot intended for auto- matic landing, although the remaining equipment can easily beadded at a later date to up-grade the system. Neither does all the equipment have to have the same level of multiplexing as thatpart which is actually involved in the final automatic sequence. Whereas a triplex channel will, following a failure of one channel,continue to operate automatically undisturbed, a duplex channel will simply disengage altogether, leaving the aircraft in a trimmedcondition ready for the pilot to take over. The initial scale of equipment for the Trident will comprisea duplex autopilot; duplex yaw-damper and single Mach stabilizer; duplicate compass system; triplicate attitude-reference system(three Sperry VG.102 vertical gyros); duplicate air data system; single flight director system; single Smiths Para-Visual Directorsystem; duplex Smiths automatic throttle control system; and a triplex Standard Telephones radio altimeter installation. Should the duplex autopilot disengage, the pilot should be ableto complete the landing visually, but he will be assisted by the PVD indicators, which will be immediately uncovered and areoperated by a separate computer. Altimeter signals would not be lost, because of th; triplex installation. There is therefore adegree of second stand-by. If the pilot for some reason decides to overshoot, he has simply to open up the throttles to full power.It is significant that de Havilland state that it is possible to re-engage the "good" half of a duplex channel after a failure"provided that the aircraft is adequately safeguarded by other means against a run-away fault of the single channel." Thisappears to imply some form of monitoring for each sub-system in a multiplex channel as well as cross-checking inherent inmultiplexing. The acceptance by the pilots of the Trident automatic flare-outsystem is going to be a determining factor in the timing and rate of introduction of full automation. Ref 1 2 3 4 5 6 7 Pilot Function Engage "Autothroute," engage "Glide," set in landing conditions Select "Land" Check radio altimeters Disconnect roll channel Keep aircraft aligned with runway Kick-off drift Apply brake, keep straight Autopilot Function Hold approach air- speed, hold glide-slope and totalizer beams Hold glide-slope and localizer beams Glide-slope signal dis- connected, Constant attitude held. Radio altimeters connected to landing computer Flare-out started Throttles to idle. touchdown completed Means of Monitoring Automatic Control Reference to a.s.i.. throttles moving. Ref- erence to flight com- pass and visualinformation Reference to flight com- pass Radio height indicators Reference to attitude director and flight com- pass, checked by visual information Reference to visual in- formation and Para- Visual display Th rottle position. r.p.m., visual informa- tion Gyropilot for the Piaggio P.166 FOLLOWING recent successful trials in a Piaggio P. 166 nowdelivered to the Consolidated Zinc Corporation of Australia, the Sperry AL.30 Gyropilot has been certificated for operation inthis type of aircraft. Another AL.30 is to be fitted in the United Steel P. 166 and the equipment is to be an accepted optional extra.The AL.30 has also been specified by the Italian Air Force for the military P. 166, a substantial number of which are likely to beordered. AUTOTHROTTLE ENGAGED. LANDING CONDITIONS SET AUTOPILOT COUPLED TO G SLOPE AND LOCALISER Plan and elevation of an autoflare approach to a 6,000ft runway with 1,500ft undershoot and 2.000tt overshoot areas, normal approach lighting and stan- dard ILS. The bold figures in the frames refer to the stages listed in the table, which show the pilot's and autopilot's actions and the means of monitoring operation GLIDE SLOPE SIGNAL DISCONNECTED CONSTANT ATTITUDE HELD R ALTIMETERS CONNECTED TO LANDING COMPUTOR AND FLARE-OUT COMMENCED. THROTTLES BROUGHT BACK. KICK-OFF DRIFT TOUCHDOWN 600 ELEVATION CATH CHECK RADIO ALTIMETERS APPLY BRAKE. KEEP STRAIGHT DISTANCE FROM TRANSMITTER 12 1000 APPROACH LIGHTS °ft o o o a o - "VJTH PATH TT- LOCALISER OVERSHOOT' KEEP AIRCRAFT ALIGNED WITH RUNWAY 5 KICK-OFF DRIFTDISCONNECT ROLL CHANNEL 4
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