52-15-01 BOEING: Applies to all model 377 Airplanes with Hamilton Standard Propellers.
Items 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 April 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 (see AD 52-13-02) and the following instructions which pertain to 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.
A. If any multiple pin connector assemblies are used in the reversing solenoid circuits, they are to be modified as specified in item 2 of attachment A.
B. Modify the following terminal strips as specified in item 1 of attachment A:
(1) Terminal strip at RH and LH wing break junction shield.
(2) Terminal strip at pilot's pedestal.
C. Protect the following exposed terminals as specified in item 3 of attachment A:
(1) Exposed terminal to which the solenoid valve leads are connected on "A" relays in propeller relay shield.
(2) Exposed terminals at throttle reversing switches.
D. Reversing solenoid circuit wiring shall comply with Boeing Service Bulletin No. 79 unless the circuits are completely isolated from all other circuits. The shielding on the wire shall be grounded at both ends and a protective cover shall be provided over the shielding wherever it runs in conduit with other wires.
E. Other circuit modifications: All airplanes shall be modified to comply with Hamilton Standard Service Bulletin No. 221.
II. Pedestal assembly. Make one of the following modifications:
A. Increase the height of the quadrant stop at the positive idle position by 1/8 of an inch. In addition, change the present positive taper on the stop and the sliding member of the throttle to a zero taper or a negative taper of not more than 3 degrees.
B. Add a plate to throttle quadrant. The plate is to be hinged at its rearward edge and its forward edge should be so located that it will act as a stop in the forward idle position. It shall not be possible to force the plate open solely by pulling rearward on the throttles. In addition, remove the positive taper from the existing quadrant stop and the sliding member of the throttle and provide a zero taper or a negative taper of not more than 3 degrees.
III. Maintenance practices (to be instituted not later than August 1, 1952):
A. At each nearest scheduled service to 350 hours:
(1) Inspect all points specified in items IB and IC. The inspections of item IB 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.
B. At 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 for inspection. Damaged wiring is replaced as necessary.
C. At 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 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. In the event the modifications outlined in A or B are not completed in accordance with B. If the Pedestal assembly is modified in accordance with item IIB, the operating instructions for airplanes so modified shall specify that the plate be open for takeoff and that it shall be closed immediately following takeoff. The plate shall remain closed during all other regimes of flight except that it shall again be opened just prior to landing.
V. (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 ability to feather even when the reversing solenoid is energized, are still under consideration and may be the subject of a future Directive.)