Several safety features are built into the tripod jacks. A locknut (also called a ring or collar) on the ram mechanically locks the ram in position. The locknut prevents the ram from settling in the event of hydraulic failure or inadvertent lowering. A safety bypass valve in the system bypasses fluid from the pump or ram when excessive pressure is built up. Airframe (tripod) jacks are normally checked out from the SE division (AIMD) when needed. Since transporting these heavy and cumbersome jacks is a problem, they often remain in custody of an organi- zation for a prolonged period of time. The organization must be responsible for their care and cleanliness during periods when not in use. As with axle jacks, these jacks need to be load tested prior to being placed in service and annually thereafter. Special inspections are performed every 13 weeks at AIMD S/E and recorded on the OPNAV form 4790/51. Your MIM will tell you what type of aircraft jack to use at each position. When deployed, you may not be able to get the jacks that are called for in your MIM. You will have to refer to the index and Application Tables for Aircraft Jacks, NAVAIR 19-70-46. It was prepared under the direction of the Commander, Naval Air System Command, by the Naval Air Engineering Center. It contains a list of approved prime and alternate jacks for all Navy and Marine aircraft. PREOPERATIONAL INSPECTION The same basic safety precautions apply to all jacks. Conduct a good preoperational inspection before you use it. NAVAIR 19-600-135-6-1 is the general preop maintenance requirements card (MRC) for all jacks. Make sure that the jack has been load tested within the last 13 weeks. Next, if the jack is dirty, take the time to wipe it down. You can’ t see cracks or broken welds under dirt. If the jack is covered with hydraulic fluid, you can suspect it may be leaking. Inspect it more closely. Check the reservoir; it should be full with the jack ram fully collapsed. If the reservoir is low, you can suspect a leak somewhere. Fill the reservoir with clean, fresh, hydraulic fluid. Check the filler plug vent valve to make sure it is not clogged. If the plug is blocked, you may get an air lock, and the jack may not operate correctly. You could also get a pressure buildup in the reservoir and a possible rupture. Check the pump handle for bends and the pump rocker arm and link for elongated or out-of-round holes. These are signs that the jack may have been overloaded, and that the safety bypass valve is malfunctioning. With the filler plug air vent valve open and the release valve closed, pump up the ram and check for leaks and full extension. When the ram reaches full extension, you will feel the pumping pressure increase. Don’t continue to pump or you may damage the internal ram stops because there is no load on the jack. Lower the ram and screw out the extension screw, but don’t forcibly overextend it past the internal stops. Check to see that it is clean and oiled. If it is dirty, wipe it clean and coat it with a light film of MIL-L-7870 oil. On jacks equipped with wheels, check the wheels and springs suspension assemblies to make sure they’re in good condition. Towing or dragging these jacks around with broken wheels will damage the frame or reservoir. Since many leaks in jacks will only appear when the jack is under a load, be sure to watch for leaks when you are jacking the aircraft. If you find a leak, or other defects, during the preoperational inspection, do not continue to use the jack Down or red line it, tag it as bad, report it, and turn it into the SE division (AIMD) for repairs. Don’t leave a defective jack where someone else may use it. HANDLING AND MOVEMENT Handling airframe jacks can be hazardous. The jacks are heavy–anywhere from 110 to 900 pounds-and the wheels are free-swiveling and small. Directional stability is poor, and pushing one into position around an aircraft is no simple chore. Trying to move or position a tripod jack by yourself is hazardous. If the jack is dirty and covered with grease or fluid, it’s even more hazardous. The jack footplates and wheels at the base of the tripod stick out, and are notorious “foot-crunchers” and “shin-knockers.” It’s not hard to damage an aircraft tire, wheel brake assembly, hydraulic lines, landing gear door, or any other pact of an aircraft if you’re not careful and ram it with a jack. Movement of jacks aboard ship when there is any pitch or roll of the deck is extremely hazardous. Even with a calm sea, a smart turn into the wind by the ship while you’re moving an airframe jack can be disastrous. Movement of jacks from hangar to hangar, through hangar bays, and across hangar tracks and ramp seams can easily damage a jack and put it out of commission–just when you need it! 3-40