Page:CAB Accident Report, National Airlines Flight 23.pdf/4

 Investigation of the No. 1 cylinder exhaust push rod housing revealed an upper hose seal improperly installed and secured. The housing and hose had been installed approximately ¼ inch too low, preventing the upper end of the housing from being sufficiently sealed by the hose and clamp installation. Due to improper installation and normal engine vibration, the connection was opened in flight allowing oil to leak from the housing as it drained from the rocker box assembly and to blow over the No. 1 and No. 9 cylinders as well as the exhaust collector ring. At least two other hose seals on the subject aircraft were found sufficiently loose to permit moving by hand, which on those clamps, was due to loss of tension of the springs. Detailed inspection of both power plants and the aircraft structure revealed no other indication of malfunction of materiel prior to impact.

Inspection of maintenance records revealed no discrepancies in either overhaul or maintenance. However, investigation disclosed that adequate supervision of lesser skilled employees was not always provided during engine disassembly. In one instance it was observed that an apprentice mechanic was responsible for a disassembly crew in one of National’s overhaul shops. The spring clamps employed on the hose seals require a special tool both during installation and disassembly if the clamps are to retain their required tension and are to be reinstalled, yet investigators of the Civil Aeronautics Board observed instances in which pliers were employed in the removal of those clamps during tear-down.

The installation of the new oil hoses and clamps at Jacksonville was accomplished by two certificated mechanics. Step ladders were used on which to work, and hand-flashlights were necessary because of the darkness. A defective spring clamp hose seal was located on No. 1 cylinder exhaust push rod housing which permitted oil leakage during the preceding flights. Two