Page:CAB Accident Report, Standard Airways Flight 388C.pdf/18

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July 30, 1963

Dear Mr. Chairman:

This supplements our July 8, 1963, acknowledgment of your letter dated June 14, 1963, reference B-1-96, concerning brake failures of Curtiss propellers on Lockheed 1049G alrcraft.

Based on the recommendations made by the Civil Aeronautics Board and our investigation of the recent accident at Manhattan, Kansas, on May 28, 1963, and incident at Elkins, West Virgina, on June 3, 1963, involving Standard Airways Lockheed 1049G aircraft, made in conjunction with CAB and Curtiss investigators, we have instituted the following corrective measures.

Regardlng the November 10, 1958, Seaboard and Western accident at New York International Airport, the CAB Aircraft Accident Report, File No. 1-0116, adopted March 22, 1960, indicated the probable cause was an unwanted propeller reversal and a contributing factor was the inadequate overhaul procedure employed by the propeller manufacturer. The CAB analysis noted that the wear of the rotor spline and mating speed reducer sleeve was of sufficient magnitude to cause complete disengagement between the power unit motor assembly and the speed reducer, thus preventing electrical control of the propeller. The analysis also stated these conditions would permit the centrifugal forces on the blades to move them to the flat pitch position and beyond. Action by this Agency resulted in issuance of Airworthiness Directives 58-25-2 and 59-7-1 requiring inspection of the old motor and speed-reducer spline couplings and AD 59-18-3 which required installation of modified oilbath-lubricated spline couplings. Mechanical low pitch stops were not required on the basis of satisfactory service experience of other Curtiss propeller models equipped with the modified spline couplings. This decision has been amply supported by service Attachment A (page 4 of 6)