Figure 19. Time history of MD-11 Flight Deck Simulation PCA landing, Flaps 28, no wind or turbulence.
Continuous light turbulence and occasional upsets from thermals occurred; however, PCA performance was judged adequate to proceed to PCA landings. On the .rst intended landing (.g. 20), initial lineup and .ightpath control were good. Based on simulation experience, the pilot selected a .ightpath of –1° at 140 ft AGL. The .ightpath overshot to approximately –0.5° and then began to decrease back through the –1° command. At 30 ft AGL, the sink rate was increasing to 8 ft/sec, so the safety pilot, as briefed, made a small nose-up elevator input, then allowed the airplane to touch down under PCA system control. The touchdown was 25 ft left of the runway centerline, 5000 ft from the threshold at a sink rate of 4.5 ft/sec. The MD-11 was stopped using reverse thrust and brakes but no spoilers or nosewheel steering.
The second landing, shown in .gure 21, was accomplished using a slightly different .ightpath control technique. Pilot A made small track changes to maintain runway lineup and set the .ightpath command at –1.9° for the initial part of the approach. Airspeed was 175 kn. At 200 ft AGL, based on the experience with the .rst landing, the pilot shallowed the .ightpath to –1° , and at 100 ft to –0.5° . The airplane touched down smoothly on the centerline at a 4 ft/sec sink rate, 3000 ft from the threshold with no inputs from the safety pilot. Note the upset from a thermal updraft that caused the airplane bank angle to increase to 8° at 100 ft AGL; the PCA track mode corrected without any pilot input. The airplane was stopped using reverse thrust and light braking but no .ight control inputs. Pilot A rated the pitch control as excellent and the lateral control as adequate on this landing.
From the two landings in light turbulence, it was observed that PCA generally controlled track and pitch to within ± 0.5° of command (disregarding the 1° bias in the track command). EPR values on approach were approximately 1.15, and variations were normally approximately ± 0.1; a 0.4 EPR differential thrust was used to correct for the thermal upset. Ground effect was similar to that seen in the simulator.
Later in the day, additional Flaps 28 approaches were conducted at Edwards AFB by pilot C. By this time, the afternoon turbulence activity had increased so much that the new pilot using the PCA mode had dif.culty adequately maintaining a stable approach. Next, three approaches with .aps and slats retracted were conducted with a go-around at 200 ft AGL. The .rst approach was at Edwards, and the last two were at Yuma. The results from all three approaches indicated that the aircraft, using PCA system control, arrived at a suitable position to land on the runway. PCA system operation was also evaluated en route from Edwards to Yuma using all the PCA modes. Testing during this period included phugoid investigation, step responses, rudder trim offsets, and frequency sweeps.
The only signi.cant problem encountered in PCA testing to this point was the sluggish and dif.cult-to-predict lateral control on approaches in turbulence. Pilots found that three or four approaches were required before adequate lineup was consistently achieved.
Pilot A, the NASA project pilot, had extensive PCA simulator experience and .ight experience before attempting actual landings, and thus did not represent the experience level of a pilot who might actually be making an emergency landing. However, pilot D had an opportunity to .y the PCA system on the MD-11 with only a few approaches in the simulator. The following text describes the .rst four approaches in the MD-11 by pilot D.
The approaches were made with a weight of 410,000 lb and a CG of 24 percent. Continuous light-to-moderate turbulence from thermals occurred, and lineup was complicated by the use of runway 03L at Yuma, which has a relatively short straight-in approach because of its proximity to the Mexican border. The .rst approach with Flaps 28 at 170 kn was not lined up well because the new pilot had dif.culty using the track mode on an approach with a short sharp turn to .nal; it was aborted at 300 ft AGL, displaced 200 ft left of the runway centerline.
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