HUMAN FACTORS

Human factors played a part in some of the key issues that have already been discussed above. Examples are: confidence in lift-fans, concern for approach to the fan-stall boundary, high pilot workload tasks, and conversion controller design.

The human factor issue that concerned the writer the most was that of the cockpit arrangement. An XV-5A and its pilot were probably lost because of the inadvertent actuation of an incorrectly specified and improperly positioned conversion switch. This tragic lesson must not be repeated, and care­ful human factor studies must be included in the design of modern lift-fan aircraft such as the SSTOVLF. Human fac­tor considerations should be incorporated early in the design and development of the SSTOVLF from the first simulation effort on through the introduction of the production aircraft. It is therefore the writer’s hope that SSTOVLF designers will remember the past as they design for the future and take heed of the "Lessons learned.”

Fatal Accident #1

One of the two XV-5As being flown at Edwards AFB during an official flight demonstration on the morning of April 27, 1965, crashed onto the lakebed, killing Ryan’s Chief Engineering Test Pilot, Lou Everett. The two aircraft were simultaneously dem­onstrating the high-and low-speed capabilities of the Vertifan.

During a high-speed pass, Everett’s aircraft pushed over into a 30° dive and never recovered. The accident board concluded that the uncontrolled dive was the result of an accidental actu­ation of the conversion switch that took place when the air­craft’s speed was far in excess of the safe jet-mode to fan-mode conversion speed limit. The conversion switch (a simple 2- position toggle switch) was, at the time, (improperly) located on the collective for pilot "convenience.” It was speculated that the pilot inadvertently hit the conversion switch during the high-speed pass which initiated the conversion sequence: 15° of nose-down stabilizer movement was accompanied by actuation of the diverter valves to the fan-mode. The resulting stabilizer pitching moment created an uncontrollable nose – down flight path. (Note: Mr. Everett initiated a low altitude (rocket) ejection, but tragically, the ejection seat was improp­erly rigged…another lesson learned!) As a result of this acci­dent, the conversion switch was changed to a lift-lock toggle and relocated on the main instrument panel ahead of the col­lective lever control.