52-13-02 LOCKHEED: Applies to All Constellation (49 Series) Airplanes With Hamilton Standard Reversing Propellers.
Items I, II and III 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 November 1, 1953.
I. In 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 specific features to be considered in isolation of the circuits. Airplanes which have other features not specifically referred to in this list shall be treated in an equivalent manner:
A. The multiple pin connector assembly at the reverse coordinating relay panel must comply with item 2 of attachment A.
B. Protect the following exposed terminals as specified in item 3 of attachment A:
(1) Exposed terminal on "A" relay in reverse coordinating relay panel;
(2) Exposed terminals at throttle reversing switches (not required if item IIA(1) is installed).
C. Modify Hamilton Standard relay box, where used, to shield the reversing solenoid circuit relay contacts, etc., 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.
D. Reversing solenoid circuit wiring: Modify in accordance with item 4 of attachment A.
II. Other circuit modifications:
A. All airplanes shall be modified in one of the following ways:
(1) Install an additional switch in the reversing solenoid circuit which will prevent the application of power to the circuit until the switch has been closed by operation of the landing gear actuated throttle reversing lock system, or
(2) Comply with Hamilton Standard Service Bulletin No. 221.
III. Pedestal design (same compliance date as item I):
A. Reversing throttle switch and lock bar assembly: Modify the assembly by adding stop pin and plate for the lock bar and cutting clearance notches on No. 1 and No. 4 switch triggers.
IV. Maintenance practices:
A. At each nearest scheduled service to 350 hours:
(1) Inspect the points specified in item IB and any other critical points in the systems where two or more solenoid wires run together. These inspections may be discontinued if the modifications made to the system are of the type described in item 1(a) or 1(b) of attachment A.
(2) 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 operation 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.
(3) If item IIA(1) is installed, perform an electrical check of the switch to assure that it opens when the throttle lock bar is in the locked position.
B. At any time that an electrical fault occurs in a circuit which is carried in the same bundles or the same conduit 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 be replaced as necessary.
V. Operating instructions: Comply with item 5 of Attachment A.
VI. (Note: Propeller governor design changes which are under development and whose purpose is to provide a high pressure hydraulic circuit bypass to safeguard against inadvertent reversing and to provide ability to feather even when the reversing solenoid is energized, are still under consideration and may be the subject of a future Directive.)
ATTACHMENT A
Criteria for isolation of reversing circuits at terminal points and connections:
1. Terminal Strips. The following methods of isolation can be used:
(a) Elimination of connections at terminal strips by using continuous wiring,
(b) Providing separate, covered terminal strip for reversing lead connections,
(c) Isolating the solenoid lead stud, terminals and associated hardware from all other nearby studs or terminals by enclosing these components in an insulating cover which is so designed orsecured to the wiring that the wire will stay in place in case of breakage at the terminal or so that the broken wire and terminal will remain insulated by the cover from contact with other circuits if the wire comes off its terminal. The nature of the cover design or provisions for its attachment must be such that its installation will not be overlooked during maintenance,
(d) Removing or grounding studs adjacent to solenoid valve lead stud and securing all adjacent wiring and the reversing solenoid lead to prevent contact of broken leads with reversing solenoid terminal or contact of broken reversing solenoid lead with other terminals. If the adjacent studs are grounded, rather than removed, the studs must be identified distinctively so that they will not inadvertently be used for the attachment of wires serving other circuits.
2. Multiple Pin Connector Assemblies. The following methods of isolation can be used:
(a) Elimination of pin connectors by using continuous wiring,
(b) Providing separate pin connectors for each reversing solenoid circuit,
(c) Deactivating all pins adjacent to the one carrying the reversing solenoid circuit. These pins are to be retained in the connector but identified distinctively so that they will not be used inadvertently. When distinctively identified, these pins may also be used for circuits which cannot supply sufficient energy to actuate the reversing solenoid or circuits which are energized only when reversing is desired. At the points where wires are attached to the connector pins, all exposed metal parts are to be protected with insulating covers so secured that contact between circuits cannot occur in case of failure at the connection or in case foreign material is left in the connector assembly.
3. Exposed Terminals on Relays and Switches. Protect these terminals in either one of the following ways:
(a) As specified in item 1(c) for terminal strips, or
(b) If the terminal is a type which cannot be protected as specified above, cover all exposed metal components with insulating material and secure all wires so that no wire can touch another terminal if the wire breaks or falls off its own terminal. Install insulating barriers as necessary to prevent inadvertent contact between broken or loose wires and other terminals.
4. Reversing Solenoid Circuit Wiring. Modify in one of the following ways:
(a) Physically isolate the wiring from all other circuits.
(b) If the wiring is run in bundles with other wires, a shielded wire is to be used. The shielding shall be grounded at both ends and a protective cover shall also be provided over the shielding. The shielding shall be carried as close as possible to the terminal points.
5. Operating Instructions. Not later than August 1, 1952, all operating instructions regarding unfeathering procedures shall specify that the following practices are to be observed and shall indicate that the reason is to guard against inadvertent reversing during the unfeathering operation:
(a) If unfeathering is being accomplished at night the wing illumination lights or landing lights are to be used to permit observation of propeller operation.
(b) The propeller is to be watched during unfeathering and the button is to be released when rotation starts. (This should normally be in 1 or 2 seconds.)
(c) The tachometer is not to be used as a guide for determining when unfeathering is to be terminated.