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Aviation History
1965
1965 - 0075.PDF
International, 14 lanuary 1965 45 ONE-ELEVEN BLIND LANDING THAT automatic landing is a desirable capability for all cate-gories of transport aircraft is now beyond serious doubt; thefacility is even being developed for application to the smallest of executive jets. Nevertheless, the path to full "zero-zero" weather minima is still a long one—though well defined for the BAC One- Eleven. While this new short-hauler is now on the eve of commercial service, one test aircraft is being made ready for actual low-weather- minima trials. The first stage, using minima of 100ft cloudbase and i-mile visibility, should be approved before the next European winter. Development flying to the stage 2 minima of 100ft/280yd (with Type 4 equipment, described later) should begin next January. How feasible are automatic approach and blind-landing systems? The answer, of course, lies in the acceptable failure rate. BAC has assumed (in line with the airworthiness authorities) an acceptable dangerous failure rate of not more often than once in 10m landings. The common electronic autopilot forms the basis of most currently proposed automatic approach and landing systems, yet with present production and inspection techniques the mean time between failures is 250hr to 500hr, giving, in the present context, an unacceptable incident expectancy of 1 in 10,000. However, a duplicated self-monitoring system (as in the VC10 for instance) can meet the 1 in 10m safe landings requirement even with an equipment mean-time-between-failures of only 26hr per channel. The aircraft's basic systems, on which the automatic controls rely, obviously must be no less reliable. The One-Eleven has a fail-safe structure and fully duplicated and independent systems. Other notable features are: considerable surplus electrical generating capacity; the minimizing of the work-load of two-man crews; and an unsurpassed field of view from the flight deck. Good flight-deck visibility is fundamental to correct pilot participation in automatic approaches and landings. The One-Eleven is the first aircraft to meet the FAA's vision requirements without concession. The 20° downward view below the fuselage datum (compared with 10'-15' on most current jets) permits an additional 100yd of approach lighting to seen at 100ft on finals. British research into blind landings has been under way for at least ten years. The only major change of principle has been that high-precision ILS developments have replaced the leader cable for azimuth guidance of the aircraft. A Standard Telephones ILS localizer at Hum achieves centre-line displacemsnts of less than 5ft. Eventually, six types of automatic approach equipment will be approved and offered to One-Eleven customers. The likely weather minima for each system have been assessed by BAC following informal discussions with the ARB, BLEU and the MoA. One-Eleven Typs 1 automatic approach equipment comprises the standard Elliott 2000 basic autopilot with separate pitch and azimuth computers and pitch monitor. Ths fully proven system will have an autopilot break-off point no highsr than 150ft and will be cleared for 200ft/J-mile weather minima. Typs 2 will simply have the addition of a lateral monitor on the autopilot (and an advanced flight director) to give a completely disturbancs-proof disconnect in the event of a runaway. Weather minima will not be less than with Type 1 but the autopilot will be cleared down to the beginning of flare-out at 50ft. The addition of a single autothrottle unit, radio altimeter and monitored radio, to form the Type 3 system, will permit a halving of the weather limits to 100ft/i-mile, but still retains the 50ft autopilot disengage point. The autothrottle working from air-data sensor inputs will control speed to within 3kt; the recommended STR 53-A radio altimeter has already produced accuracies of ± lft at touchdown over many thousands of BLEU and FAA trials. Automatic touchdown, in simplest form, will first be offered by the Type 4 equipment (Type 3 with the addition of single-channel auto-flare). Automatic flare is achieved by fesding the autopilot with the commands of a self-monitored computer programmsd to the exponential flightpath flare-out (as developed by BLEU) and The various phases of a One-Eleven automatic landing. The complete approach and landing sequence is as follows. First set runway heading, tune ILS and localizer. Set the approach speed and engage autothrottle. Select the glideslope to "auto" (situation display unshutters). At or before reaching the glideslope, select final approach flap and undercarriage down and adjust airspeed. Check radio altimeters with test switch. Engage second pitch channel and check automatic change-over. Assume azimuth control and continue to land if all indications satisfactory at break-off height. Check flare initiation. Disconnect automatics after touchdown I5OO'-2POO' AE>ROX. 30 SEC. RISK PERIOD FINAL AIRCRAFT CONFIGURATION- FULL FLAP AND APPROACH SPEED I 3 VMS CHECK PITCH AUTO CHANGE OVER BOTH AUTOMATIC SYSTEMS SELECTED AUTOMATIC GLIDE SLOPE ENGAGEMENT RADIO ALTIMETER SIGNALS APPEAR ON SITUATION DISPLAY f I 1150'-2OO'(AUTO-APPROACH BREAK-OFF HEIGHT) ABOUT IOO' SO' RUNWAYATTITUDE I HOLD PHASE FLARE PHASE THROTTLESCONFIRM FLARE1 MANUAL AZIMUTH RESUMED I GLIDE SLOPE START CLOSING SUPPRESSED TOUCH DOWN FULL PILOT CONTROL RESUMED
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