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Aero Precision provides OEM part support for military aircraft operators across more than 20 aircraft


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Showing content with the highest reputation on 07/13/2021 in all areas

  1. First question is what year/model? Yes it matters if its a B-model verse a mid 80s H-model. Ground test valve commonly considered bad for transfers and to be honest it almost never is. Check the rigging to the ground test valve. It should be tighter on one cable verse the other so that the valve wants to pull to the closed position. The incorrect rigging of the cable is much more common than a valve itself. Check the brake shuttle valves. These can transfer aux to utility and utility to aux when brakes are used. They should not allow fluid to flow through them once they shift to other side of shuttle. A strange one that I have seen is one of the brake selector valves not receiving power to close so both valves were open and causing util/aux brake pressure to fight at the shuttle valves. Its easy to check. They are powered close so when energency is selected, you should have 28 vdc on normal selector and opposited when normal is selected. Nose landing gear uplock, NLG actuator and nose gear emergency selector valve can also cause this. Not too common but I have seen it. Do you have UARRSI, refuel pods or weapons systems? If so, all of those can be points of transfer. Emergency brake and normal brake accumulators should be checked for internal leakage as well. Most common of all is a person not fully depleting brake pressure on BOTH normal/emergency before moving the ground test. There is always some avionics or electrics guy that wants to help but doesnt know the details of running hydraulics. I have seen people chase this ghost and come to find out the new guy was improperly trained on tying ground test.
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