Page:CAB Accident Report, Eastern Air Lines Flight 304.pdf/23

 of this is illustrated by the captain involved in the turbulence incident in N8607 at Dulles. He stated that "…we encountered the most violent jolt I have ever experienced in over 20,000 hours of flying.

"I felt as though an extremely severe positive, upward acceleration had triggered off a buffeting, not a pitch, that increased in frequency and magnitude as one might expect to encounter sitting on the end of a huge tunningtuning [sic] fork that had been struck violently.

"Not an instrument on any panel was readable to their full scale but appeared as white blurs against their dark background.

"From that point on, it could have been 10, 20, 60 or 100 Seconds, we had no idea of attitude, altitude, airspeed or heading. We were now on instruments with no Visual reference and continued with severe to violent buffeting, ripping, tearing, tending crashing sounds. Briefcases, manuals, ash trays, suitcases, pencils, cigarettes, flashlights flying about like unguided missiles. It sounded and felt as if pods were leaving and the structure disintegrating.

"The objects that were thrashing about the cockpit seemed to momentarily settle on the ceiling which made it impossible to trust ones senses although I had a feeling that we were inverted as my seat belt was tight and had stretched considerable. As my briefcase was on the ceiling, I looked up and through the overhead (eyebrow) window and felt that I was looking down on the top of a cloud deck. (The first officer) later said he had the same impression at the same instant as we acted in unison applying as much force as we could gather to roll aileron control to the left. The bariton bar at this time started to stabilize and showed us coming back through 90 degrees vertical to a level attitude laterally. At this time, I had my first airspeed reading decaying through 250 knots. The air smoothed out and we gently leveled off at between 1,400-1,500 feet…."

In further attempts to assess the Combination of turbulence and handling characteristic elements of the man-machine-environment triangle, the Board found two other discussions by the research pilot significantly important. "In our experience we find that slightly positive static margin… is an area where pilots get into more difficulty than zero static margin, or even considering slightly unstable. What happens is that, especially in large aircraft, We have these slow response characteristics… as long as you fly an airplane and don't try to force it–you allow the airplane to respond well within its capabilities–you don't have any difficulty If you, however, try to force the airplane to respond faster than it wants to, then you can get into what we call a low frequency pilot-induced oscillation. It is nothing more, really, than overcontrolling. You don't see the airplane respond immediately so you have the tendency to put a little more elevator in, and by this time the airplane has started to respond and you suddenly find the response is more than you wanted. So the tendency is to reverse the process…. I can see this situation can be quite critical in turbulence or possibly under IFR conditions plus turbulence where, let's say, you do have some large gusts which change your attitude appreciably if the pilot attempts to… maintain his attitude tightly, there is a possibility that he can get himself involved in a PIO." As amplification of this thought and in answer to a question concerning pilot comments, the witness, citing