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.
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
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.
Dont 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 dont 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 theyre
in good condition. Towing or dragging these jacks
around with broken wheels will damage the frame or
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. Dont leave a defective jack where someone
else may use it.
HANDLING AND MOVEMENT
Handling airframe jacks can be hazardous. The
jacks are heavyanywhere 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, its even more
hazardous. The jack footplates and wheels at the base of
the tripod stick out, and are notorious foot-crunchers
and shin-knockers. Its not hard to damage an aircraft
tire, wheel brake assembly, hydraulic lines, landing gear
door, or any other pact of an aircraft if youre 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 youre 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
commissionjust when you need it!