-20-
1000 feet. Captain O'Brien further stated that "it was absolutely impossible to have control of the turning radius of the airplane and control of the ascent and descent at all times"; this he attributed to an "extremely strong rotary pressure" that resulted in the airplane making flat turns. First Officer Crabtree testified that they encountered only the one updraft followed by the steep left bank, the loss of air speed, the subsequent spin, and recovery. It is impossible to conclude from this testimony whether the airplane was actually in a spin or making a number of flat turns in rapid succession. However, from the testimony it would appear that if the airplane was in a spin it was a relatively flat one and at a relatively low air speed with a small inclination of the longitudinal axis to the horizontal. We have found no record of any occurrence of this sort involving large modern multi-engine aircraft. In spite of a careful analysis of the record, we find it impossible to reach a definite conclusion on this point.
After giving proper weight to the testimony of Captain O'Brien and First Officer Crabtree, the passengers aboard the aircraft, and the four Eastern Air Lines pilots, and to the meteorological analysis, we conclude that the airplane encountered severe turbulence. However, it is impossible to determine with any degree of certainty the intensity of the turbulence and for this reason we cannot reach a conclusion as to whether Captain O'Brien exercised that degree of skill which could reasonably be expected of an airline pilot while the airplane was in the line squall. Captain O'Brien stated in his testimony that he observed a cloud formation extending across his course out to sea and inland indicating a frontal condition to be entered at right angles. Since in this instance the flight was at right angles to the line squall, a left turn probably served to keep the flight in the turbulent area for a longer period than would have been the case if the flight had continued on its original course. Moreover, in making a turn in such conditions, the difficulty of keeping the airplane under control is increased as the power required to maintain level flight in a banked turn is greater than in straight flight and the stalling speed is increased.
In conclusion, it must be said that this accident was the result of lax operating procedures and a severe weather condition. The most clearly remediable factor is, of course, the operating procedures of Eastern. In fact, this accident might have been prevented if Eastern's operations had been so conducted as to insure the pilot's receiving such information and instructions as were, or could reasonably have been expected, to have been available to ground personnel. Special caution in these matters should always be displayed when flights are dispatched over routes where they may encounter distinctly unfavorable weather conditions such as a cold front or line squall type of thunderstorms.
III
CONCLUSION
Findings
We find, upon all of the evidence available to the Board at this time, that the facts relating to the accident involving NC 21727, which occurred about 10-1/2 miles west-southwest of Vero Beach, Florida, on April 3, 1941, are as follows:
