Page:Civil Aeronautics Board accident investigation report, National Airlines Flight 2511.pdf/6

 structure was severely crushed at impact. The firewall was ruptured at two places in the lower inboard area as a result of impact. The ground fire had entered zone 3 through these openings and burned part of the propeller control relay junction box. No other zone 3 components were fire damaged. The firewall contained no evidence of fire burning through the structure itself.

The outboard sections of the accessory cowlings remained on the engine and were severely fire damaged. The inboard accessory cowlings were detached at impact. They were excessively oil coated on the inner surface but showed no evidence of fire damage.

The No. 4 powerplant was located approximately 600 feet southwest of the No. 3 engine. This powerplant was buried approximately six feet in a water-filled crater and was found in a nosedown and inverted position. This powerplant had separated with its nacelle structure attached to the engine mount. There was no evidence of fire either prior to or after ground impact.

All of the powerplant and propeller assemblies evidenced severe ground impact damage. Upon disassembly and inspection, however, no evidence was found of internal failure, operating distress, or other malfunction. All of the main bearings, master rod bearings, and other bearings were found to be in place and adequately lubricated. Examination of the main screens and sump plugs failed to reveal any evidence of any foreign material or contamination.

All of the propeller assemblies remained in place with their respective engines. All blades exhibited impact damage in varying degrees and two blades of the No. 3 propeller assembly evidenced paint smears on their face side as a result of contact with fuselage structure.

The four propeller assemblies all evidence severe ground impact damage. Examination of the dome assemblies, pitch changing mechanisms, stop levers, barrel halves, and spider assemblies failed to show any evidence of any malfunctions or pre-impact failures. Examination of the slip ring assemblies, thrust bearings, and washers, and remaining components of the propeller assemblies showed no indication of inservicein-service [sic] difficulty.

The blade shims and shim plates of the four propeller assemblies showed that the respective blade angles at ground impact were: 30 degrees, 30 degrees, 45 degrees, and 34 degrees. The No. 4 propeller assembly showed light impact markings on the shim plates at 50 degrees and also had heavy indentations at approximately 34 degrees.

The No. 1 propeller governor was broken from its pad at impact and was not recovered intact. The No. 2 propeller governor was examined and the speeder rack spring measurement was equivalent to 2240 engine r. p. m. The No. 3 propeller governor speeder rack spring position also indicated 2240 engine r. p. m. The speeder rack spring in the No. 4 propeller governor was intact in its housing and measurement of the rack spring position indicated 2240 engine r. p. m. also.

The fuel tank compartments in the wings were damaged to various degrees at impact. The fuel tanks in the entire left wing area between the front and center spars were severely broken apart at impact. The fuel tank compartments in the right inner wing were also severely damaged. The fuel tanks in the wing outboard of the No. 4 engine