B. R. Allen, George S. Moore, C. W. Walker

“ During the course of our continuing investigation of the accident involving a United Air Lines Vickers Viscount aircraft near Parrottsville, Tennessee, on July 9, 1964, at was revealed, during static and flight tests, that certain discrepancies existed in the Pyrene fire extinguisher. The most serious of these discrepancies was the spraying of CO2 into the cockpit area when extinguishers are discharged. This was determined to have been due to leakage at either the bayonet floor fitting or at the valve in the head of the discharge bottle. ”

“ Brass terminal blocks attached to each end of the seal are connected to electrical wiring in the discharge head for normal electrical discharge. When the discharge button is pressed in the cockpit current flows through the seal diaphragm which acts as a resistance and results in heating the seal. When the temperature rises sufficiently, the metal is softened and the 200 psi pressure in the extinguisher causes the seal to rupture and the CO2 flows into the underfloor compartment. ”

“ Therefore, the Board recommends that the Federal Aviation Agency evaluate the design of the Pyrene Duo Head Model DCD-10 fire extinguisher system and take such corrective action as will increase its reliability and prevent release of CO2 into the habitable portions of the aircraft. ”