CIVIL AERONAUTICS BOARD
BUREAU OF SAFETY
October 9, 1964
Mr. George S. Moore
Director
Flight Standards Service
Washington, D. C. 20553
Dear Mr. Moore:
During the Board's investigation of the recent accident near Parrottsville, Tennessee, on July 9, 1964, involving a United Air Lines Vickers Viscount, N7405, several static and inflight tests were conducted on the fire extinguishing systems for the underfloor cargo compartment using similar aircraft. The results of these tests pointed out certain discrepancies which could seriously affect the safety of the aircraft and passengers.
At least fifteen fire extinguishers, Pyrene Duo Head Model DCD-10 were discharged during the static and inflight tests. This extinguisher is located behind the first officer on the right hand side of the flight deck companionway. Connection of the extinguisher to the underfloor cargo compartment spray tube assembly is accomplished by means of a flexible hose between the bottle discharge head and a bayonet floor fitting. This arrangement allows the bottle to be utilized as a portable extinguisher should the need arise. All of the static tests were conducted with the flexible hose configuration. United Air Lines replaced the flexible hose with a rigid tube for the inflight tests.
The most serious discrepancy noted during the tests concerned spraying of CO2 into the cockpit when extinguishers were discharged. At least five of the fifteen tests resulted in the gas escaping into the cockpit where CO2 concentrations in the atmosphere at head level were measured at maximum values of 12 percent. This leakage occurred at the bayonet floor fitting on the flexible hose installations and at the valve in the bottle discharge head of the extinguishers with the rigid tube installation. In each of these cases very little of the CO2 was discharged into the under-floor compartment.
