Portal:Civil Aeronautics Board

“ Here again, as in the case of lightning, direct research is difficult, but a substantial amount has already been accomplished. We believe it important that the existing store of knowledge of the nature of atmospheric turbulence, of its structure when its severity is at a maximum, and of its effect on the flight performance and the control of the aircraft should be extended as rapidly as possible. ”

“ In undisturbed air, at 6000 feet, the maximum rate of climb of a fully loaded aircraft of the type involved in this accident is approximately 600 feet per minute at take-off power. Even with one engine dead, the maximum rate of climb would be over 100 feet per minute. If the airplane had flown out of a rising current in front of the storm and directly into rapidly descending air, approximately as it entered the rain, it is conceivable that it might have been impossible, even with the application of full power, for the pilot to avoid a rapid loss of altitude. ”

“ There is no reason to believe that any electrical effect of lightning other than accoustical shock may have been even a contributing cause of the accident.
The optical effect of lightning, or of any sudden and bright light, is well known. Mrs. Everhart testified, that the lightning flash which occurred in the vicinity of the airplane while she was watching from a distance of about 11⁄2 miles was so brilliant that she was blinded for a brief time during which she lost sight of the airplane. ”

“ The experience of pilots flying in the vicinity cannot be relied upon completely in arriving at a conclusion as to the presence of turbulence. Experience shows that of two airplanes flying at the same altitude at the same time, a very short distance apart, one may encounter very severe turbulence while the other may be operating in comparatively smooth air. Therefore, it is impossible for us to arrive at a definite conclusion that the pilot of Trip 19 was flying through conditions of severe turbulence just prior to the crash. ”

“ Pilots quite frequently have reported that when a flash of lightning has passed near their planes they have felt a slight "bump." This would be a result of the pressure wave, but all available data indicate that there never have been any serious effects upon the stability and flight path of an airplane from this cause. We do not believe that lightning itself produced such severe turbulence as to have caused or contributed to this accident. ”

“ The past record of safety of air transportation within the United States, extending to over 130,000,000 miles of transport flying without serious injury to any person in the 17-month period immediately preceding the present accident and to thirteen years of operation without fatal accident by Pennsylvania Central Airlines and its predecessors, is a sufficient evidence that only the highly exceptional or the hitherto unknown would produce so tragic an effect. ”

“ Not only would the interruption of oil thus tend to invite overspeeding but the interruption itself could be caused by the same maneuver which created the acceleration. If the airplane went into a sudden dive a momentary interruption of oil could be caused by the negative acceleration which would create a movement of oil away from the oil outlets in the tank, exposing the outlets to air. That such a condition is possible is borne out by the testimony of witnesses during the hearing. ”

“ It is quite likely that if a material loss in oil pressure was indicated shortly after taking off, Captain Scroggins would have returned to the Washington-Hoover Airport. When this fact is considered with the evidence to the effect that the condition of both right and left engines after the accident was almost identical, the conclusion seems clear that the condition of the oil filter prior to departure from Washington could not have had any bearing upon the cause of the accident.
No reason has been found to suspect an engine failure while in flight. ”

“ Stalling due to turbulence, without there having been any ice on the wings to increase the susceptibility to such stalling, is extremely rare, but cannot be absolutely eliminated as a possibility.
When an airplane of the type involved in the Lovettsville accident is deliberately stalled with power on, the stall customarily develops first on one wing-tip and that wing drops sharply, the airplane simultaneously turning toward the low wing. ”

“ Experts testified that the nature of lightning illumination was especially injurious to human eyesight and a considerable number of pilots have reported temporary impairment to their eyesight from lightning flashes near their aircraft while in flight for varying lengths of time depending upon such conditions as the brilliance of the flash, whether the pilot was looking directly at the lightning, the degree of darkness in the cockpit and outside the plane. ”

“ The first type of lightning may set a tree on fire, whereas the latter type may splinter a tree and toss heavy pieces of wood a considerable distance away. Brief, powerful discharges set up pressure waves with characteristically steep fronts which are capable of a damaging effect at a short distance away from the path of the lightning itself. It should be noted that a single lightning discharge may involve not only mechanical but also thermal and electrical effects. ”

“ The wobble pump control is located forward of and on the lefthand side of the jump seat and all are easily accessible as a support to one sitting in the jump seat if he finds it necessary to hold on to something. Since the occupant of the jump seat was not a pilot and had not ridden frequently in airplanes, consideration was given to the possibility that he might have grasped the flap control in order to steady himself if the airplane had been passing through turbulent air conditions and the possible effect such action could have had upon the flaps or the controllability of the airplane. ”

“ Where the maneuver is deliberately executed by a pilot who is prepared to initiate immediately the required measures of recovery, evidence received in the present investigation indicates that only from 400 to 600 feet of altitude is normally lost in restoring normal flight. The intentional stall, being initiated with the airplane's nose pointed up at a steep angle, does not strictly simulate the conditions of an inadvertent stall due to gusts encountered while in level or nearly level flight. ”

“ While the conclusions of the National Advisory Committee for Aeronautics indicate that heavy rainfall will not disturb the performance or behavior of an airplane such as a DC-3 to any marked degree, the Committee believes that heavy rainfall would have a substantial effect on the performance of the airspeed indicator. Beyond a certain critical combination of airspeed and rain density, the airspeed head will flood and the water will accumulate in the pressure line. ”

“ The sludge or sediment content which might be collected in an airplane engine would depend largely upon the usage of the engine, particularly the amount of power applied over extended periods. In other words, if the engine is operated at a high rate of horse power over an extended period of time, more sludge or sediment can be expected than if the engine is operated under lesser horse power conditions. If the cuno type filter which was installed in aircraft NC 21789 was free of sediment to an extent which would permit a normal oil pressure of 60 lbs. ”

“ If the pilots were blinded by a lightning flash their immediate concern would have been to avoid stalling of the airplane while their disability continued. In seeking to be perfectly safe on that point they might have over-corrected by pushing the machine into a dive, and with both pilots pushing on the control column together the force required might have been overlooked under conditions of such stress and the dive continued until the ground was reached. ”

“ The thermal effect of lightning is recognized in the electrical and radio systems of airplanes through burnt fuses, melted or destroyed wires, and other damage of a like nature, and there may be similar effects upon other parts of the airplane's structure, controls, or equipment. ”

“ Past experience has failed to reveal any case where lightning has caused the fuel of an airplane to catch fire while in flight, nor is there any record of any other serious form of fire in flight from this cause. ”

“ Following its arrival in Washington, the airplane was serviced with gasoline and oil and was given a routine "turn-around" inspection. This inspection consists of a general visual examination of the airplane, especially of the propellers, wing and tail surfaces, and the controls which are visible from the outside, and the testing of the controls, engines, instruments, and radio equipment. In addition, the interior of the airplane is cleaned and the outside surfaces wiped off. ”

“ The trip departed from the ramp at Washington-Hoover Airport at 2:05 p.m. having been delayed awaiting a local passenger. After taxiing out to the take-off position and running the engines up preparatory to taking off, the oil gauge for the right engine showed that the oil pressure in that engine was below normal. The airplane was then taxied back to the loading ramp where, at the request of the pilot, a Pennsylvania-Central Airlines mechanic made the appropriate adjustment to the oil filter to relieve it of any sediment which might be interfering with the oil flow. ”

“ A number of these witnesses stated that, while they had not noticed much lightning in connection with the storm, they recalled a violent flash of lightning and the sound of thunder which was immediately followed by an extraordinarily loud roar of motors. Some of these witnesses in the immediate vicinity of the point of impact testified that the loud roar of motors was followed by a "crash" or "blast".
Mr. I. W. Baker, who lives about 31⁄4 miles almost due south of the scene of the accident watched the storm with "rolling and tumbling" clouds come across Short Hill. ”

“ The drag effect varies with the size of the rain drops, but, assuming that the rain consisted entirely of large drops, the power absorbed by the rain while substantial, would be less than the power reserve available. Even if the reserve power were not drawn upon, the path angle and rate of descent would have to be maintained for several minutes and over a distance of several miles to force an airplane down from 5500 feet above the ground. ”

“ Undoubtedly the Board's statutory duty was thus defined in the Act in recognition of the fact, well known to the Congress, that due to the meager and inconclusive character of the evidence available, the circumstance surrounding air accidents have at times been enshrouded in obscurity. Probability flows from evidence which inclines the mind to a conclusion but leaves room for doubt. ”

“ While the electrical effect of lightning frequently produces a magnetic field which may temporarily or permanently influence metal parts, compasses, or other instruments, there is no record of serious results therefrom on aircraft in flight. ”

“ Since we are here necessarily dealing with occurrences of extreme rarity and consequent unfamiliarity and in some instances are considering phenomena of nature wherein the knowledge of men still remains extremely limited, it is inevitable that much of what follows must appear highly speculative. However, the inherent difficulties presented by the limited evidence available in the present case must not deter us from a full exploration of every possibility and an attempt to reach a conclusion as to what probably occurred to produce the accident. ”

“ If the particular discharge of lightning with which we are concerned in this investigation were of a nature to produce a strong pressure wave, the pilots might have suffered from acoustical shock or concussion of a severity depending upon the proximity of the lightning to the cockpit and whether or not the cockpit windows were open. Experience has revealed that such pressure waves have produced severe concussion upon human beings which might result in unconsciousness. ”

“ Although it would be impossible to determine the speed at contact with any accuracy from the condition of wreckage, the completeness of the destruction at least indicated a speed far above that of ordinary flight. The damage, which technicians who have had past occasion to examine a great many wrecked airplanes that have be contact with the ground in all sorts of attitudes and at all sorts of speeds found almost unprecedented in their experience, would be difficult to with a speed of less than 300 m.p.h. ”

“ While the Members of the Board, the Examiner, and the representatives of the Safety Bureau were the only ones designated to ask questions directly of any witnesses, the presiding examiner, acting under instruction of the Board, announced at the opening of the hearing that any person who had any evidence, questions, or suggestions to present for consideration in the proceeding might submit them to the Examiner. ”