return lines. When pressure increases above 3,730 to
The wings are unlocked by lifting the wing fold
3,830 psi, the spring-loaded ball check unseats, and the
handle up and forward until it reaches the first stop.
valve relieves excessive pressure. The spring-loaded
This action operates the cable and pushrod mechanisms
ball check reseats when pressure falls to 3,360 psi.
that control mechanical locking of the wing lock
cylinders. This same action, through the pushrod
Maintenance of the wing fold system at the
connected to the mechanical locks, causes the warning
organizational level consists mainly of scheduled
flags to appear on top of the wings. Further movement
inspections, lubrication, rigging of mechanical
of the wing fold handle at this point is prevented by a
linkages, removal and installation of components, and
spring-loaded mechanical latch that blocks the crank at
analysis of system malfunctions.
the wing lock cylinder.
The MIM provides system schematics and trouble
With flight controls in the proper position and
analysis sheets to assist in pinpointing causes of
weight on the wheels, the wing fold lockpin switch is
malfunctions. A thorough knowledge of the system
placed at UNLOCK. Power is supplied to the unlock
before troubleshooting is necessary. Logical reasoning
side of the wing lock selector valve, allowing combined
plus a systematic operational checkout of the system
system utility hydraulic pressure to the four wing lock
will produce better results than trial and error
cylinders in each wing. Pressure in the wing lock
troubleshooting methods.
cylinders moves the lock shaft to retract the wing
Lack of lubrication or other required maintenance
lockpins. After completion of this action, the wing fold
at prescribed intervals will generally be reflected by
control handle can be moved to the full forward
stiff, hard-to-operate wing fold control mechanisms or
position, operating the wing fold selector valve in each
related wing fold discrepancies. Strict compliance with
wing and porting hydraulic pressure through flow
maintenance requirements, in all cases, will eliminate
regulators to the wing fold actuating cylinders, which
or minimize this possibility. All corrective maintenance
extend and cause the wing to fold.
should be in accordance with the instructions provided
The wings are spread by moving the wing fold
in the appropriate MIM.
control handle aft to the first stop, mechanically
Wing lock warning flags rarely get out of
positioning the wing fold selector valve in each wing to
adjustment, and whenever they fail to retract, it should
port hydraulic pressure through flow regulators to the
be considered an indication of failure of all locks to
wing fold cylinders, causing them to retract and spread
properly enter lock fittings. Realignment to provide a
the wings. The wing fold control handle is held at the
wing lock indication without ensuring that the wings
first stop by the retracted lockpins, which prevent
are positively locked certainly does not correct the
rotation of the lock shafts and cranks.
discrepancy and presents an extremely hazardous flight
After spreading action, the wing fold lockpin
condition.
switch is placed at LOCK, and power is supplied to the
Good maintenance practices, strict quality
lock side of the wing lock selector valve. The selector
assurance by qualified inspectors, and good super-
valve then ports hydraulic pressure to the closed timer
vision will ensure safe, timely, and quality corrective
valve in each wing fold joint. As spreading is
maintenance actions.
completed, a spring-loaded lockpin detent in each
inboard wing lock fitting is depressed by the outboard
Intermediate maintenance of wing fold hydraulic
lock fitting. When the lock fittings are aligned, the
components generally consists of installing cure-date
lockpins can extend and enter the wing lock fittings.
repair kits (sealing devices, etc.) and/or replacement of
With lockpins extended, the lock shaft is free to rotate,
miscellaneous parts available as fleet-type repair kits.
and the wing fold control handle can be moved flush
Parts in the repair kit are normally easy-to-replace
with the top surface of the center console. This action
items, which do not require the depth of disassembly
rotates the lock shafts to prevent retraction of the
and inspection necessary at complete overhaul, and are
lockpins and retracts the warning flags. When any
replaced whenever high time removal of a component is
lockpin fails to extend, the wing fold handle cannot be
necessary. Information on repair kits for various
secured, and the warning flags will remain exposed.
components is provided in the applicable "Illustrated
Parts Breakdown" and, in some cases, the
A thermal relief valve is installed in the pressure
"Intermediate Maintenance" section of the MIM and
line of the wing fold and wing lock selector valves. It
appropriate (03) overhaul manuals.
vents excessive pressure buildup because of the thermal
expansion of trapped fluid into the combined system
15-14
