55-25-03 de HAVILLAND: Applies to All Model 104 "Dove" Aircraft.
Compliance required as soon as practical but not later than February 15, 1956, unless already accomplished.
A case has recently occurred where the presence of corrosion at the main earth connection, situated on the fuselage nose decking in the vicinity of nose frame 4, has reduced the efficiency of this earthling point sufficiently to cause overheating of the cockpit lighting cables.
The de Havilland Service strongly recommends that the following inspection be carried out at the earliest opportunity in order to ascertain the condition of this connection with which the FAA concurs and considers mandatory.
Method.
1. Examine earth post situated in nose floor, and ascertain if it has a protective coating of blue oil base paint D.T.D. 827. (If it is protected, do not disturb unless it appears to be in a bad condition.)
2. If no protection is evident, dismantle terminal, clear floor surface locally at the terminal with a stiff bristle brush, to ensure removal of any corrosion and to provide good electrical contact between mating faces of terminal assembly. Reassemble terminal, using corrosion washers D.H.S. 439 G in place of lead plated brass washer 4F.781. All other mating surfaces must be clean and free from corrosion. If steel washer shows signs of deterioration, it must be replaced by another one, cadmium plated. Completed assembly must be painted liberally with blue oil base paint D.T.D. 827 to prevent ingress of moisture.
(de Havilland Technical News Sheet CT (104), No. 121, Issue 2, dated July 14, 1955, also covers this same subject.)