Page:CAB Accident Report, Eastern Air Lines Flight 304.pdf/21

 later, while awaiting the results of pertinent test, study, and research programs, several incidents and other accidents occurred under conditions bearing some similarity to the conditions associated with this accident. Not all of these cases involved the same aircraft model family, and several of the cases were at greatly different altitudes. Flight recorder readouts and crew statements were available for study in a few cases, while in others the crew did not survive and the recorder foil was destroyed or otherwise not available for study. Not all of the involved aircraft were U. S Registered. The Board does not presume to judge any investigation that may have been completed or to prejudge any that is still under evaluation. It wishes only to note here that every possible avenue of investigation that could be explored was considered during its lengthy evaluation of this accident. Although in those cases where the crew survived to relate their experiences there were many dissimilarities in the occurrences, there were a few apparent common denominators. Turbulence of varying degrees, small and large, was involved in each case, the aircraft pitch attitude, airspeed, and altitude varied greatly in both positive-negative or increasing-decreasing directions. The crews indicated that large longitudinal control displacements of both stabilizer and elevator were used and required to maintain control. In some of these cases substantial altitude losses were experienced. Generalizing from a limited number of cases not fully evaluated or clearly understood is usually a technically unsound approach, yet it is still difficult to escape concluding that the phasing relationship between turbulence-induced aircraft motion with control inputs is at least a factor in these occurrences."

Some of the preliminary results of the extensive NASA intercenter rough air penetration studies were of considerable assistance to the Board in its assessment of both the Miami accident and this one. Of particular interest is NASA's finding that pilot Workload, flight deck acceleration environment, aircraft characteristics, instrumentation displays, and piloting technique can all be factors in precipitating upsets in some cases. In the work completed it has been shown that the simulator, without any pilot control inputs, can fly through the most severe National Severe Storms Project (NSSP) gust/draft history without excessive g excursions, large airspeed variations or great altitude changes but with, in many cases, large changes in pitch attitude. The inherent or augmented stability of the simulated aircraft provides the restoring forces necessary to maintain the trim condition. In most of the trials with a pilot control input, the simulator could be flown successfully through the "storm" and the extent of the g, airspeed, and altitude excursions depended largely on how close the pilot tried to maintain the desired pitch attitude. Some of the trials revealed oscillations quite large in amplitude, indicating pilot control input out-of-phase with the simulator motions induced by the imposed gust/draft history. In a few trials the oscillations became divergent and an upset occurred. When the pilot was told to deliberately ignore the pitch attitude display and to rely chiefly on controlling airspeed during the Simulated penetration, large oscillations of all parameters invariably resulted.

In line with the accepted concept that the attitude indicator becomes the primary instrument in turbulence flying, it is extremely interesting to recall the previously mentioned display characteristics of the Collins 105 instrument installed in this aircraft and others. The gearing of the pitch bar is such that when the aircraft is being rotated to high pitch attitudes (more than 20 degrees), the ratio of actual aircraft deck angle to indicated pitch attitude increases. The result, of course, is that unless the pilot is familiar with this phenomenon,