AD 48-09-02

48-09-02 DOUGLAS: Applies to C-54 and DC-4 Aircraft.

To preclude the probability of short circuits occurring in the electrical distribution bus which runs from nacelles number one to four, and which is impracticable to protect by circuit protective devices, the following must be accomplished to assure that this bus will be in a fault-free condition.

I. Inspection required by April 1, 1948, and thereafter at intervals not to exceed 400 hours (or in the case of scheduled air carrier operators at each routine check period.)

Determine that at least 1/2-inch clearance is maintained between the bus and protuberances likely to "ground" the bus in the nacelle areas. Note particularly this clearance at the engine control pulleys and the pulley guide brackets.

II. Inspection required not later than July 1, 1948, and thereafter at intervals not to exceed 8,000 hours.

In those installations where the large No. 1/0 nacelle-to-bus feeder cables are run in metallic conduit, such cables must be pulled out for inspection. Replace by new cable ANA Spec. ANJC48a or Douglas DES SM-2001, where chafing or mechanical deterioration of the insulation is evident.

(NOTE: Oil-soaked insulation alone is not considered as sufficient cause to require the replacement of this cable.)

III. Not later than June 1, 1948.

Determine that the bus supporting brackets are of approved Douglas Aircraft Co. standard quality and that Adel or equivalent cushioned nongrounding type bus clamps are used for clamping the bus onto the brackets. Any substandard brackets and clamps must be replaced.

(Douglas Service Letter No. A214TS-1245/SRD-530 dated October 10, 1947, covers this same subject.)