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While in flight cargo door fluctuates 4 inches short of uplock


pedejd424
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Test flight procedure RCAF C130 332 E/H model. 30500 hours. On ground ramp and door control work fine when actuating door or ramp open/closed using electrical control. While in flight using ADS in flight deck ramp and door will open and close no problem. However when using door and ramp control from cargo compartment, ramp closed and locked then select door open, door reaches 4 inches short of uplock and begins to pulse up and down. If door is open and locked ramp will open normally, but when trying to close using ramp electric control ramp reaches closed position and pulses. Does anyone know of a common component that is bypassing hydraulic pressure? Additional food for thought while actuating ramp and door switches simultaneously, they will open and close without problem, providing the switches are held in position. Thanks and Hercs rule.

Edited by pedejd424
Snag resolved
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Update on this snag, Maintenance has replaced the following components, Cargo door actuator, cargo door shuttle valve, ramp and door manifold, and carried out switch adjustments. Test flight today with no change.

With ramp closed and locked the door reaches just short of the uplock and oscillates up and down. If you unlock the ramp and lower it slightly the door will completely go up and locked. Also when the door is open and locked the ramp fails to completely close and lock, once again there is a pulsation as the locks repeatedly extend and retract trying but failing to engage. If the door is closed and locked the ramp operates fine. Seems like a pressure bypass/hydraulic lock somewhere in the system.

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That doesn't sound like a hydraulic problem. To rule out hydraulics, use the manual knob and handle in flight with pressure coming from the aux pump. It sounds like an electrical problem, check the terminals on the back of the control panel, the relays up above the left paratroop door.

Also check the wiring coming from the ramp position switch running down the longeron, we had some get damaged from crews throwing the chocks up in the ribs, and it would make the ramp do funny things

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I've had some experience in this arena.

Your issue is most likely the clamps on the deice duct up in the tail. They need to be rotated. They are probably facing down, which causes the screw portion to contact the corrigated metal on the door. The clamp needs to be rotated 90' forward or aft. I don't know if the TOs specify.

We flew more than a half dozen times trying to figure that one out. A crew chief pointed it out.

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When closing the ramp and door from the back, the door must close first, then the ramp. If you don't do it that way, the air stream will cause the door to float that last 4 inches and the door will not close. Watch the ramp and door when closing, using the ADS switch, you'll notice that the door always closes first.

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Maintenance replaced aux pump. Air test no change. Operated door open and locked, ramp open and locked, ramp closed and locked, door closed and locked in that order using manual control. Test successful, isolated to electrical issue. This model has ADS arms ( anchor arms ) installed for aerial delivery, wiring diagram shows if these arms are loose when retracted or switch is minimally contacting the power is lost to the ramp solenoid.. Sure enough techs went out and rattled the arm finding circuit being opened and ramp solenoid de-energized. Switch adjustment in progress. Test flight this afternoon. Fix sounds promising since air loads when opening door with the ramp closed are different than with an open ramp, possibly affecting a minimal contacting arm switch. Update to follow and thanks smoedog for the suggestion.

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ADS arm micro switch adjustment fixed the snag. The airflow around the ADS arms causes them to flutter while the door is in transit. Extra play or an under adjusted switch caused circuit interruption when the door was opening. The RH arm switch was adjusted and air tested serviceable. Simple fix, complicated troubleshooting since snag could not be duplicated on ground. Thanks for input.

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  • 3 weeks later...

Sorry I didn't see this one sooner, I thought of that switch while reading the initial post. We've got some copies of old service manuals from back before I was born and pointed out the ADS arm switch. Pretty incredible the technology hasn't changed and is still so reliable, not to mention the guys who make sure it works!

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