Development and Flight Test of an Emergency Flight Control System Using Only Engine Thrust on an MD-11 Transport Airplane(41)

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Manual throttles-only control is extremely dif.cult, but the PCA control laws provide stable track control and show promise of providing stable .ightpath control. Using the PCA track control knob, runway alignment could be achieved and maintained. Figure 48 shows the MD-11 with a 31-in. CG offset, the left engine at idle, and the right engine being controlled by the unmodi.ed PCA lateral control laws to hold track. As seen, track control is very sluggish but it does track and hold the command with a steady-state error. A limit is apparent on roll rate with the unmodi.ed control laws. The pitch phugoid is uncontrolled and is a problem; it interacts with the lateral control.
In .gure 49, an open-loop thrust increase on the center engine (to establish a climb) fortuitously damped the phugoid. Also shown at 1965 sec is a decrease in the bank angle feedback gain from 1.0 to 0.5. This change was designed to reduce the steady-state error in track, which it did, but it also increased the amplitude of a dutch-roll limit cycle.
Control law improvements are expected to greatly improve the lateral control, and a longitudinal control law has been developed to control pitch with the center engine.
1.7
Airspeed,
kn
≈ 300
≈ 250
≈ 210

Single engine
1.5
FPA ≈ 0°
Open symbols: left engine idle
Solid symbols: left
Engine 3

engine off EPR for 1.3 wings level
Desired EPR for equal roll rates in each direction 1.1
.9

Figure 46. Effect of lateral CG offset on EPR on engine 3 required for wings-level .ight, .aps and slats up, gear up, altitude ≈ 10,000 ft, gross weight ≈ 400,000 lb, center engine idle.

Unfamiliar Crew PCA System Test
In a test designed to evaluate the need for PCA system training, a crew with no previous experience with the PCA system was exposed to a total .ight control system failure situation in the MD-11 FDS. One of the crewmembers was an MDA pilot without extensive MD-11 experience. The other was a Honeywell pilot that was familiar with normal MD-11 operation. Neither had ever seen PCA in operation.
The failure was induced soon after takeoff at Los Angeles International Airport with the gear up, Flaps 10, gross weight of 445,000 lb, and an airspeed of 230 kn. The simulation operator turned off all three hydraulic systems. A placard was exposed (simulating an electronic advisory system message) advising the crew that all three hydraulic systems had failed, and that a PCA system was available with instructions on how to engage the PCA system. The placard also referred the crew to a PCA page that could be included in an emergency procedures manual for more information.
The crew immediately engaged the PCA system and found operation similar to the normal autopilot. They continued the climb to a safer altitude, then read the emergency procedures PCA page, and planned a return to the airport. The crew leveled off, practiced with PCA operation, and were satis.ed that they understood its operation and performance. They initially decided to .y to Edwards, but to make this test more generic, they were asked to return to Los Angeles. The crew decided to .y an ILS-coupled approach at Los Angeles. The hydraulic failure had increased trim speed by 20 kn. Available information included ways to reduce airspeed; the crew used the technique of reducing the center engine to idle, which reduced airspeed by 20 kn. They also dumped fuel, reducing speed by another 15 kn to 215 kn. The crew set up a long downwind at 4000 ft, lowered the gear, and turned inbound at 20 mi to intercept the ILS. Approach speed was 210 kn, still with Flaps 10. ILS capture was nominal, and the approach was successfully .own down to 20 ft. At this point, because of the ground effect and the higher than normal speed, the airplane .oated, and with most of the runway behind them, the crew elected to go around. They stated that if

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6
Degrees 4
　
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