AD 52-20-01

52-20-01 DOUGLAS: Applies to Models DC-6, DC-6A, DC-6B Aircraft Below Serial Number 43274.

To be accomplished as soon as practicable, but not later than February 1, 1954.

To reduce the likelihood of electrical fire and the loss of electrical and electronic equipment essential to continue flight, it is necessary to provide adequate overvoltage protection. There are two systems involved, known as the "Eclipse Generator System" and the "General Electrical Generator System". The changes required in each of these systems are as follows:

Eclipse. Replace the four B-14 type generator contactors with a high-voltage (120-volt rating) contactors of sufficient capacity to interrupt an overvoltage generator. Overvoltage relays are already installed in the Eclipse system, and these should be retained.

General Electric. Install overvoltage sensing relays and either (1) replace the four generator control relays, G.E. P/N 3GTR-77A102, with a high-voltage (120-volt rating)relay of sufficient capacity to interrupt an overvoltage generator, or (2) rework the G.E. P/N XRP-12 reverses current circuit breakers so as to trip out simultaneously with the generator control relay to provide for necessary additional interruption capacity. Except for the General Electric alternate (2) fix, this same subject is described in Douglas Service Bulletin DC-6 No. 470. The General Electric Co. has service information available for the G.E. system alternate (2) rework.