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Examination revealed nothing which indicated malfunction or failure of the engines prior to the breakup sequence. There was no indication of operational distress, inadequate lubrication, or overheating. On the other hand, there were clear indications that all of the engines were operating when they tore off. The Nos. 2 and 4 fuel-trimmer actuators were positioned for reduced power.
Each propeller, except No. 3, was found attached to its respective engine. No. 3 separated in flight and was found about 775 feet from its engine. Examination indicated separation occurred when the No. 3 propeller blades struck a heavy object during the inflight breakup. This gouged the blades and caused a torsional failure of the engine reduction gearing coupling shaft. The blow also caused an elongation of the propeller blade operating dowel pin holes at a position which showed a propeller blade angle of 52 degrees.
At ground impact the NO. 1 propeller blades were positioned about 24 degrees; No. 2, about 29 degrees; No. 3, about 6 degrees; and No. 4, 16 degrees. Propellers Nos. 3 and 4 were in the ground fine pitch range. These positions, because of the numerous safeguards that prevent ground fine pitch from occurring in flight, were determined to have resulted from free fall and impact forces. Consequently, only the blade angle of the No. 3 propeller was considered valid and significant.
A review of the original certification process for the British-manufactured Viscount showed it was built to conform to the British Civil Air Requirements and issued a British airworthiness certificate. The Federal Aviation Agency, then CAA, reviewed the specifications and requirements and, when satisfied that an adequate standard of airworthiness existed, accepted the British certificate and issued the aircraft the U. S. airworthiness certificate. This process was carried out under the terms of Executive Agreement 69 of October 17, 1954. It was stated by both representatives of the British and U. S. that the strength requirements of each country are substantially the same and the Viscount met or exceeded both.
The recommended rough air penetration speed for the Viscount is about 170 knots, the last airspeed reported by Flight 75. At or near this speed the aircraft strength is sufficient that extreme maneuver and/or gust loading will stall the aircraft rather than cause a structural failure.
Autopsies were performed on all of the crash victims according to provisions of the law of the State of Maryland. At the public hearing the Chief Medical Examiner testified relative to the findings in order that the Board could avail itself of every facet of information relevant to the accident. The findings indicated that all of the occupants of the plane were killed by impact with the ground, although about 20 passengers had sustained ante-mortem injuries. The majority of the ante-mortem injuries were described as scalp injuries of the type and degree which suggested heavy bumps on the head by contacting overhead structure. Others were seat belt injuries and two or three suggested forces applied downward on the body forcing it into the passenger seat. The findings showed that some passengers were exposed to an intense flash fire which contained droplets of flaming liquid. At least 10 passengers revealed an elevated level of carbon monoxide; the highest was about 10 percent, not normally a disabling amount. The medical Examiner said the time required to attain the levels found was difficult to determine. Depending on several factors, the time could vary from eight seconds to several minutes. He indicated that the relatively few bodies showing carbon monoxide was consistent with a short period of exposure during which some passengers were affected while others in the immediate area were not. The medical
