The .rst attempted ILS landing at Edwards with .rst .are of –1.5° at 130 ft and a second .are of –0.5° at 30 ft resulted in the aircraft .oating down the runway at 10 ft AGL, as it had at Palmdale. At the 5000-ft mark beyond the runway threshold, the system was intentionally disconnected, and a manual go-around was .own. For the next ILS approach, the second .are angle was set to a slightly steeper approach, using an MCDU input.
ILS-Coupled PCA Landings
Figure 34 shows the last 83 sec of the .rst PCA ILS-coupled landing. For this approach to Edwards runway 22 with a 6-kn wind from 260° , the second .are was reduced to an FPA of –0.75° . Localizer tracking was excellent all the way to touchdown. Glideslope tracking showed a ± 0.25° wander that was typical of the coupled approaches. First .are at 130 ft and second .are at 30 ft to –0.75° reduced the .ightpath to less than 0.5° , and touchdown occurred at about 1 ft/sec on the centerline 3000 ft beyond the runway threshold. Pilot A stated that this was as good a landing as he could have made with the normal .ight controls. The cockpit views from the cockpit video camera showed runway lineup was maintained throughout the approach.
Figure 35(a) shows a time history of another ILS-coupled approach and landing. Before the time shown, the pilot had selected a track that intercepted the localizer about 12 mi from the runway, and pressed the
Touchdown
Flightpath
angle,
deg
Radar
altitude,
ft AGL
Airspeed,
kn
EPR
970616
Approach/Land button (shown in .g. 33) to arm the ILS capture mode. At localizer capture, the system rolled onto the localizer with one overshoot and maintained the selected slight descent rate until glideslope capture 10 mi out. The glideslope capture resulted in an overshoot, but once established on the ILS, localizer tracking was excellent, and glideslope tracking was adequate. The preprogrammed .ares at 130 ft and 30 ft mostly arrested the sink rate and resulted in a touchdown a foot from the centerline at 5 ft/sec sink rate, 1200 ft beyond the threshold. After touchdown, the PCA system was disengaged by moving the throttles to idle. The nose lowered and the nosewheel touched down smoothly; the pilot then used differential braking to slow and maintain directional control. Figure 35(b) shows an expanded view of the .nal minute of this landing. The higher sink rate for this ILS-coupled landing was primarily caused by the 2-sec lag in translating between the glideslope and the .rst .are. For this approach, the MD-11 glideslope was becoming more negative at 130 ft, and the lag allowed the airplane to continue to sink below the glideslope, resulting in a shorter touchdown at a higher sink rate. This transition logic could have been better re.ned for improved control (and in fact was improved for the analytical touchdown dispersion study discussed later).
Two more ILS-coupled approaches were .own with .aps and slats retracted at a speed of about 200 kn. As expected, the one-dot-low approach could not be .own because the engines were at or near idle. With the glideslope set, through an MCDU input, to 1.5 dots low, the approach worked well and was executed down to a go-around at 100 ft. Figure 36 shows this approach. A good landing could have been made from this low approach, but because of the airspeed proximity to the 204-kn tire speed limit, no landings without .aps were made. Localizer and glideslope tracking was excellent. Engine thrust was very close to idle, so signi.cant turbulence could probably not have been accommodated in this con.guration.
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本文链接地址：Development and Flight Test of an Emergency Flight Control System Using Only Engine Thrust on an MD-11 Transport Airplane(34)
