Speed Control
The third FADEC was installed on the center engine, providing the low-frequency speed control mode shown in .gure 14(a). This mode worked very well; trim speed could be changed 30 kn greater and less than the initial trim speed. FPA was maintained within 1° during speed control operation. Figure 26(a) shows a time history of a speed change from 250 to 270 kn at an altitude of 10,600 ft. Starting at 247 kn, the speed command was increased to 270 kn. The center engine, which was initially at idle, increased thrust in response to the command, while the wing engines decreased thrust to maintain .ightpath. After 50 sec, speed was 268 kn, and slowly increased to 270 kn.

1.4
1.3
1.2
EPR
1.1
1.0
.9
Left 
R ight 

Ce nter 

0 50 75 100 150 175
200
Time, sec
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Figure 22. Time history of pilot B’s third PCA approach and go-around, slats extended, .aps retracted, gear down, bank angle mode, light-to-moderate turbulence.

Altitude, ft AGL
Airspeed, kn
Flightpath angle, deg
Magnetic track, deg
Bank angle, deg
EPR
2000 1500 1000 500 0 190
185
180
175 2 0
–2
–4 40 30 20 10
0 20 10
0
–
10

–
20

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1.3
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1.0
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5 nmi
Ground

Altitude, ft AGL
Flightpath angle, deg
Airspeed, kn
Magnetic track, deg
EPR
2000 1500 1000 500 0 4 2 0
–2
–4 160
155
150
145 228 226 224 222 220
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1.1
1.0
.9

970606
30 x 103 24 and 32 percent CG
20
Altitude, ft
10
0 100 200 300 400 Airspeed, kn
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PCA landings

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PCA approaches with no flaps, slats only, and rudder offset

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PCA ILS-coupled autolands

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Demonstration to 16 pilots, airlines, DoD, FAA, and industry

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Later, the speed command was increased to 300 kn, which was achieved with the center engine near maximum continuous thrust and the wing engines near idle.

High-Altitude Testing
PCA was tested at 15,000, 20,000, and 30,000 ft. Contrary to predictions from the simulation, operation was good; FPA was somewhat less damped at the higher altitudes but still adequate. Lateral control was adequate as well.

Tests at Aft CG
At 30,000 ft, the CG was shifted from 23.6 to 31 percent, and step response tests were conducted. Response was good. Pitch step response was only slightly less damped than at the mid-CG conditions. This lack of sensitivity to aft CG was primarily because of the low-slung engines providing pitching moment without a speed change. Figure 26(b) shows a time history of PCA performance at 29,000 ft with the CG at 31 percent. The speed control mode was engaged. A 180° turn was commanded; differential thrust was commanded to roll to the 20° bank limit, which took approximately 12 sec. Roll-pitch coupling caused a small FPA decrease; 150 ft was lost. The increased thrust caused a speed increase, as it did at low altitudes (.g. 18). The speed control loop reduced the center-engine thrust to hold speed. Once stabilized in the turn, the FPA converged to level .ight and held it well. During the turn, a –1° FPA command was made. Response was good, similar to that at low altitudes and mid-CG conditions (.g. 16). Center-engine thrust decreased to idle to hold airspeed. During the rollout, a 0.5° pitchup occurred, and the 150 ft lost on the turn initiation was recovered. Although overall performance was slightly degraded, it was still certainly adequate and better than the simulation predictions.

1.0
.5 Flightpath angle, deg
　
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