Page:CAB Aircraft Accident Report, Northwest Airlines Flight 705.pdf/22

 Consequently, rejected an unknown cause determination as an evasion of its responsibli1ties. When further detailed study showed that the general causal area involved the man—machine—environment relationship, the Board concluded that a meaningful probable cause could be formed around this finding. There is no doubt that a longitudinal upset did occur. There is no doubt that the severe weather was instrumental in producing the upset. Also, there is little doubt that the aircraft characteristics had a significant bearing on the pilot's control displacements and on the final noseover maneuver. Accordingly, the Board has concluded that the unfavorable interaction of high vertical air currents and large longitudinal control displacements resulted in the longitudinal upset. Since the Boeing recovery calculations indicate that a successful recovery might have been possible, the Board has preferred to avoid stating that a successful recovery could not have been made although there are some reasons to believe this latter possibility is more nearly correct. In any event there is no intended implication that the pilot did not do everything possible to regain and maintain control under the most unusual conditions and circumstances

This report would be incomplete if it did not include some discussion of the Board's views on the corrective actions that should be considered if accidents of this type are to be prevented in the future. From the preceding discussion of the evidence in this case, it should be evident that there is no simple panacea that will assure prevention of upset accidents. Since it is indicated that the cause lies in conflicting interrelationships of man-machine-environment factors, it must be realized that improvements in each and every one of these areas are required to raise the overall "system reliability" and to preclude other occurrences. One can easily be beguiled by undue emphasis on, or defense of, one aspect of the overall problem neglecting the other aspects, with the result that no improvement in safety is achieved.

It has been heartening to the Board to note that since the accident the entire aviation community has devoted considerable attention and effort to the upset problem, and that many, real safety changes in today's operations have been brought about as a result of this concerted industry effort. Among the many programs initiated by the FAA, their program for educating the pilot to the potential hazards of turbulence has received, perhaps, the greatest attention. Many Safety bulletins dealing with piloting technique and aircraft characteristics have been circulated to the pilots, and FAA inspectors have been instructed to insure proper attention to the problem in airline training programs. Plans underway to expedite the remoting of USWB weather radar displays on ATC radar scopes are expected to result in better weather information being relayed to flights. FAA‘s assistance to NASA in an intercenter rough air penetration program has enabled NASA to proceed expeditiously with that program. Finally, FAA has taken the initiative in stimulating the industry to develop improved attitude indicators. The broad, comprehensive NASA rough air penetration progiar has already produced extremely significant data, and is being continued in an effort to provide more information on the involved fundamentals. The aircraft manufacturers have developed improved recommended rough, air penetration techniques, and have restricted aircraft nosedown electric stabilizer trim limits so as to reduce the likelihood of serious out-of—trim conditions. The USWB is actively engaged in many turbulence research programs, all aimed at developing beeter understanding of the basic problem. Airlines have devoted increased attention to turbulence in their training programs with the result that the pilot group today is more aware of the hazard and the proper techniques for safe penetrations