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Figure  4-3-13.  Center Cargo Hook and Cargo Hook Release
4-3-16.  Cargo Hooks Operational Check.

TM-1-1520-240-10 Army CH-47D Heilcopter (EIC:RCD) Manual
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TM  1-1520-240-10 4-3-18            Figure  4-3-14.  Forward and Aft Cargo Hooks CAUTION The forward and aft hooks may fail to open if  the  slings  are  slack  when  the  release solenoids are energized (a load of approx- imately  20  pounds  is  required  for  open- ing). The hooks can be opened by select- ing  the  desired  hook(s)  and  depressing the release switch as the aircraft is lifted to apply tension to the slings. e. CARGO HOOK EMERG Switch.  The emergen- cy cargo hook release switch is on the CARGO HOOK control  panel.  It  is  a  guarded  switch  and  it  is  labeled EMERG REL ALL (emergency release all). The switch is used to simultaneously open the three hooks, if an emer- gency situation develops. The three hooks will open re- gardless of CARGO HOOK MSTR or HOOK SEL switch positions. Setting the switch to REL ALL, energizes an emergency hook release relay. The relay then energizes release  solenoids  in  the  forward  and  aft  hooks  and  a solenoid valve in the center hook. The solenoid valve in the center hook releases the aircharge stored in the low- er half of the hydraulic actuator, transferring the charge to the upper (release) half of the actuator to open the hook. After this method of opening the hook, the hook actuator must be recharged to 2,000 to 2,100 psi. The emergency hook release relay will automatically deener- gized after a 10 second time delay. This prevents dam- age to the hook release solenoids. CAUTION Before  external  load  operations,  crew– members    shall    familiarize    themselves with the manual emergency cargo release mechanism installed on the helicopter WARNING When  the  center  cargo  hook  is  opened with the external load off the ground, the cargo hook will whip back back and forth. CAUTION When the center cargo hook is opened us- ing the manual emergency release handle, the hook must be closed manually. No at- tempt should be made to close the hook using the normal hydraulic or pneumatic method, since damage to the cargo hook can result.







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