Use airframe (tripod) jacks for lifting the entire aircraft off the ground or deck. Airframe jacks are commonly called tripod jacks. You may hear them called wing, nose, fuselage, or tail jacks. These names come from the jack placement on the aircraft. The points for jacking vary with the type of aircraft, and can be found in the MIM for each type of aircraft. There are two different types of tripod jacks-fixed height and variable height, Both are mobile, self-contained, hydraulically operated units. They consist of three basic assemblies. These assemblies are the hydraulic cylinder, the tubular steel wheel tripod leg structure, and the hydraulic pump. The main difference between the two types is that the tripod structure on a variable height jack can be adjusted to different height by adding leg extensions.

All model designations for tripod jacks begin with the letter T, for Tripod, such as T10-2FL or T20-1VH5. The number following the T indicates the jack capacity in tons, such as 10 for a 10-ton jack. This is followed by a dash (-) and the specific jack identification number. Then comes two letters indicating the type of tripod jack (FH = fixed height, or VH = variable height). The number that follows the VH for variable height jacks indicates the number of leg extension kits available for that jack. Figure 3-28 shows a T20-1VH5 jack with only two of five extension leg kits installed. Each leg extension kit increases the effective height of the basic jack by 18 inches. The airframe tripod jacks weight varies from 275 pounds to 837 pounds.

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 Center. It contains a list of approved prime and alternate jacks for all Navy and Marine aircraft.