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were eight instances of early removals. Half of these had not attained the pretriously prescribed overhaul interval without needed repair. Additional importance must be attached to this record of reliability when it is realised that there is no secondary or backup proViSion for the mix box, synchronising shaft, or either trmsndssion. The satisfactory performance of these comments is essential to the safe Operation of this helicopter. On November 6, 1963, the Board recommended a EGO—hour overhaul lmtation on aft transmissmns and mix boxes. (See Attachment B.) To date this recommendation has not been fully unplemeﬂted. (See Attachment C.)

It was acknowledged by the FAA witnesses at. the public hearing that verbal approval of TBVZLSiDnS to the Operations Specifications-Maintenance, which was given New York Airways orallyr by an FM. maintenance inspector was not in compli— ance with existing regulations which required written approval of the SuperviSing inspector. The requirement for written approval does incurs that the superv1Sing inspector, removed from the day—touday contact With the carrier, will be able to alternate an independent check on the recommendations of the inspector in charge Wl‘bh respect to liberalizations in the carrier's Operations Specifications.

Probable Cause

The Board determines the probable cause of this scoldent was fatigue failure

of the drive quill shaft due to contamination of the lubrication system in the aft transmiss1on assembly.

BY THE CIVIL AERONAUTICS BOARD:

/s/ ALAN S. BOYD Chaim

/s/ ROBERT T. mars! Vice Chainsan

/s/ our answer Member

/s/ o. JOSEPH MINETTI Member

/'s/ warmer GILLILLAND Member