AD 48-25-01

48-25-01 DOUGLAS: Applies to All C54-DC Series and DC-4 Airplanes Prior to Serial Numbers 43095, Operated in Scheduled and Nonscheduled Air Carrier Passenger Service.

Compliance required by May 1, 1949.

Because of previous fires and the fire hazard which exists in zone 3, it is necessary that the following be accomplished:

1. To increase the effectiveness of the fire warning system in the nacelles, seven fire detector units must be installed in the nacelle (zone 3) aft of the firewall at the following approximate locations:

(a) 1 unit at the top of nacelle approximately 15 inches forward of the front spar.

(b) 1 unit at each wing section fireseal.

(c) 1 unit at the aft end of the nacelle area under the fuel tank and near the fuel supply lines.

(d) 3 units on the aft face of the firewall (one near the top and one at each side.)

These fire detectors should be connected into the existing engine accessory compartment fire detector circuit, and the entire system wired into the circuit of the audible warning system.

(Douglas Service Bulletin DC-4 No. 60 covers this same subject.)

2. Revise the present fire extinguisher system in nose wheel well in order to install two additional 15-pound CO2 bottles. Provide additional plumbing aft of the firewall in each nacelle by running a perforated line across the top of the nacelle directly aft of the oil tanks and then diagonally aft and down to a point under the bottom wing skin aft of the front spar, at which point it will cross the nacelle and run diagonally forward and up to the original starting point. The discharge pipes tee into the present 3/4 ring O.D. supply pipes for the accessory section. All aluminum CO2 supply pipes between firewall and front spar and between the inboard and outboard fireseal ribs of each nacelle are to be replaced with steel pipe.

(Douglas Service bulletin DC-4 No. 67 covers this same subject.)