52-14-01 DOUGLAS: Applies to All DC-6, DC-6A and DC-6B Airplanes With Hamilton Standard Propellers Except as Otherwise Indicated. \n\n\tItems I and II are to be accomplished by means of a progressive modification program to be submitted to and approved by the FAA. This program shall begin no later than August 1, 1952, and shall be completed no later than August 1, 1953. \n\n\tI.\tIn order to prevent inadvertent actuation of the propeller reversing solenoid valves, protect the reversing solenoid circuits from all other electrical circuits and protect the reversing solenoid circuits from each other. This is to be accomplished in accordance with attachment A and the following instructions which pertain to some of the specific features to be considered in isolation of the reversing circuits from other circuits. Other features which are not specifically referred to in this list shall be treated in an equivalent manner: \n\n\t\tA.\tModify the following multiple pin connector assemblies as specified in item 2 of attachment A (See AD 52-13-02 Lockheed for Attachment A): \n\n\t\t\t1.\tFirewall connector (if the reversing solenoid lead has not already been removed). \n\n\t\t\t2.\tConnector at the front of the control pedestal. \n\n\t\t\t3.\tConnector at Hamilton Standard relay box (if used). \n\n\t\tB.\tModify the following terminal strips as specified in item 1 of Attachment A: \n\n\t\t\t1.\tFirewall junction box terminal strip (if used). \n\n\t\t\t2.\tTerminal strip at synchronizer compartment (if used). \n\n\t\t\t3.\tTerminal strip within propeller control box located behind pilot's seat. \n\n\t\tC.\tProtect the following exposed terminals as specified in item 1(c) of Attachment A: \n\n\t\t\t1.\tExposed terminals at secondary throttle lock relays located behind pilot's seat. \n\n\t\t\t2.\tExternal A2 and A3 terminals on "C" relays in propeller control box behind pilot's seat. \n\n\t\tD.\tHamilton Standard reversing relay box (if used): Reversing solenoid circuit relay contacts, etc., to be shielded from all other circuits which are energized at any time except when reversing is desired. Reversing relay boxes which have separate pin connectors for the reversing solenoid wire and the remaining circuits shall be so installed that it will not be possible inadvertently to interchange any connectors on any two relay boxes. \n\n\t\tE.\tPressure seal disconnect: Modify in one of the following ways: \n\n\t\t\t1.\tBypass the pressure seal by using continuous wiring. \n\n\t\t\t2.\tProvide a separate connector for the reversing solenoid lead. \n\n\t\t\t3.\tPins adjacent to the reversing solenoid pins shall be deactivated or used only in circuits which cannot provide sufficient energy to activate the reversing solenoid or circuits which are energized only when reversing is desired. Also, provide an insulating shield for the reversing solenoid pins on both sides of the pressure seal. The reversing solenoid wire shall be secured to this shield or in some equivalent manner to prevent the wire from falling free in casethe terminal pin comes out of the socket. \n\n\t\t\t4.\tIsolate the solenoid valve lead insert on both sides of the seal by covering both the socket and the wire terminal with insulation which will cover all exposed metal parts when the wire is in place, when the wire terminal has come out of the socket, or when the wire is broken at any point up to the point at which it is secured in the bundle. The nature of the insulation or the provisions for securing it in place must be such that its installation will not be overlooked during maintenance. \n\n\t\tF.\tReversing solenoid circuit wiring: Modify in accordance with item 4 of attachment A. \n\n\t\tG.\tOther circuit modifications: \n\n\t\t\t1.\tAll airplanes with fuselage numbers below 233 shall be modified to comply with Hamilton Standard Service Bulletin No. 221. \n\n\tII.\tReverse solenoid lock assembly: \n\n\t\tA.\tComply with Douglas Service Bulletin DC-6, NO. 356, dated March 9, 1949, to prevent excessive deflection of lock assembly components.B.\tThe "Reverse operable" warning device shall be clearly visible when the lock is open just a sufficient amount to permit pulling the throttles into the reverse regime. \n\n\tIII.\tMaintenance practices (to be instituted not later than August 1, 1952): \n\n\t\tA.\tAt each nearest scheduled service to 350 hours: \n\n\t\t\t1.\tInspect all points specified in items IB, IC, and IE. These inspections may be discontinued if the modifications made to the system are of the type described in item E1 or E2; item 1A or 1B of attachment A and item 2A or 2B of attachment A. \n\n\t\tB.\tAt any time that an electrical fault occurs in a circuit which is carried in the same bundles or the same conduits as the reversing solenoid circuit, representative terminal points in the faulty circuit are to be inspected to determine whether any damage may have occurred within the bundles or conduit. If there is evidence of possible damage, all the wiring involved is to be removed and inspected. Damaged wiring is to bereplaced as necessary. \n\n\t\tC.\tAt each nearest scheduled service to 350 hours, perform an electrical check of the reverse safety switches in the pedestal assembly to assure that the switch is open when the throttles are moved forward out of the reverse position, unless it is shown that failure of any of the reverse safety switches to open will be clearly apparent to the flight crew by reason of improper operations of the propeller control system. Because of the many technical considerations involved, analyses showing that the objective of this revision has been accomplished should be referred to the FAA for engineering evaluation and approval. \n\n\t\tD.\tConduct the mechanical functional test specified in AD 50-16-01 at each nearest scheduled service to 350 hours. \n\n\tIV.\tOperating instructions: Comply with item 5 of attachment A. \n\n\tV.\t(NOTE: Propeller governor design changes, which are under development and whose purpose is to provide a high pressure hydraulic circuit bypass tosafeguard against inadvertent reversing and ability to feather even when the reversing solenoid is energized, are still under consideration and may be the subject of a future directive.)