Touchdown,
4.5 ft/sec, 25 ft left of centerline 800 600 400 200
0
0
–1
–2
–3 226
225
224
223
5
0
–5 6
4
2
0
5
0
–5
1.3
1.2
1.1
1.0
.8
0 25 50 75 100 125 Time, sec
970602
Touchdown on centerline at 4 ft/sec sink rate
Command
Measured
Command
Measured
Therm al upset 2
Rudder
Aileron Elevator
Reverse
Left thrust
Right
Center
was reached well before lineup. Once on the glideslope, the engines were near idle and lateral control was very poor. This approach crossed the runway threshold 300 ft AGL and was aborted.
The third approach by pilot D was .own with .aps up but slats extended at an airspeed of 180 kn to simulate operation in the enhanced mode discussed earlier. In this case, the pilot was to use the PCA system FPA mode for pitch and the bank angle mode for lateral control. Figure 22 shows the time history and cockpit views at four times on the approach. Turbulence is evident in the airspeed excursions of ± 2 kn. Lateral deviations were mostly held within the 200 ft width of the runway, and the airplane was near the centerline when the 200-ft go-around altitude was reached. Bank angle commands were generally within ± 5° , and bank angle control was sluggish but tracked well. Pilot D commented that he had a mild pilot-induced-oscillation tendency in the lateral axis as he learned to compensate for the sluggish lateral performance. EPR averaged 1.05 with the .aps retracted. A PCA go-around was made at 200 ft AGL; the airplane was near the centerline as it crossed the threshold, as shown. In this third approach, the pilot had begun to learn to compensate for the sluggish lateral control.
The fourth approach (.g. 23) was .own by pilot D with Flaps 28 and a 1.5° offset on both rudders to simulate yaw asymmetry of the United Airlines .ight 232 accident situation. This approach, using the track mode, was lined up well throughout, indicating the improvement as pilot D became familiar with the lateral response. Once established on .nal, there was considerable engine activity because of turbulence, even though only very small pilot track changes and no .ightpath changes were made. The left engine averaged about 0.1 EPR lower (about 10,000 lb thrust) than the right to counter the rudder offset. Note the ± 2-kn airspeed changes from the turbulence, the increased average airspeed of almost 10 kn on the glideslope, and the extensive EPR activity to maintain control in the turbulence. A PCA go-around was initiated at 200 ft AGL. Go-around performance was good; approximately 60 ft was lost before achieving a positive rate of climb.
In smooth air, new pilots could make successful PCA approaches on their .rst try. Figure 24 shows the .rst approach of pilot E, one of the demonstration pilots. This pilot had a brief simulator session but no previous .ight experience with the PCA system. He engaged the PCA system on the base turn, used the PCA system FPA and track modes, used 1° and 2° track changes, and reached the predetermined go-around point near the runway centerline. One other demonstration pilot had similar success in smooth air.
PCA System Envelope Expansion
In October 1995, following successful completion of the PCA landings, PCA operation was tested beyond the original design envelope, as summarized in .gure 25. Based on simulation results, PCA performance was expected to degrade as altitude increased because of slower engine response and degrading dutch-roll characteristics. PCA was tested at mid and aft CGs, at altitudes from 200 to 30,000 ft MSL, at speeds from 160 to 360 kn, with a 1.5° rudder offset, with a 7° aileron offset, and with all hydraulics off. Approaches were .own with a takeoff .aps setting of 28° , with slats only, and with no .aps or slats. The center engine was used for speed control. PCA engagement in mild upset conditions was tested.
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