TM 55-1520-240-23-10
16-2
EXTERNAL CARGO HOOK SYSTEM RELEASE MODES
16-2
NORMAL RELEASE
The hook release system is normally operated from
either cockpit or cabin. Selection of the hook or hooks
to be released is made at a five position rotary HOOK
SELECT switch on the overhead panel in the cockpit.
Switch positions are FWD, MID, AFT, TANDEM, and
ALL. The position of this switch determines which hook
opens when the CARGO HOOK RELEASE switch on
either control stick or the hoist operators grip is pressed.
The switch operates through a dual hook relay box
containing relays and three maintenance indicator lights.
NO BREAK - WORK HARDER
Actual release of the hook or hooks is done from the
cockpit or cabin. Cockpit release is made by the CARGO
HOOK MASTER switch on the CARGO HOOK panel.
The switch has three positions ARM, RESET and OFF.
When the switch is set to ARM, power is applied to the
CARGO HOOK RELEASE switches on the cyclic sticks
and also to the CARGO HOOK ARMING switch at the
hoist operators station. OFF position is used to close
the mid cargo hook. RESET position is used to turn off
the HOOK OPEN caution lights. Cabin operation is by
a switch on the hoist operators grip.
NO BREAK - WORK HARDER
The forward and aft hooks are electrically released. The
center hook is hydraulically released through a solenoid
valve in the tunnel area.
NO BREAK - WORK HARDER
Three indicator lights on the master caution panel
show if any of the three hooks are open. A fourth light
indicates a fault in dual hook operation. It comes on to
show if one of the hooks is not prepared to open.
EMERGENCY RELEASE
In an emergency, all three hooks can be released at the
same time from a switch on the overhead panel in the
cockpit. It is a guarded switch marked EMERG REL
ALL. The switch releases all three hooks regardless
of the position of the HOOK SELECT switch. Setting
the switch to REL ALL, energizes an emergency hook
release relay. The relay then energizes electrical release
solenoids in the forward and aft hooks and a solenoid
valve in the center hook. The solenoid valve in the
center hook releases an aircharge stored in the lower
half of the hydraulic actuator, transferring the charge to
the upper release halt of the actuator to open the hook.
NO BREAK - WORK HARDER
After emergency release, the forward and aft hook will
relatch automatically. The center hook must be manually
reset and recharged with air to 2,000 to 2,200 psi.
16-10
