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PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
P. Tires
Tubeless tires are designed to permit any air or nitrogen that is trapped in the cords or that diffuses
through the liner to escape through special sidewall vents. This venting prevents pressure build-up
within the cord body which might cause tread, sidewall or ply separation. Discounting tire growth after
initial inflation, once the tire has been inflated, the maximum permissible pressure drop due to diffusion
is 5% in any 24 hour period.
Vent holes penetrate the sidewall rubber to, or into, the cord body and may vary in size, depth and
angle. Therefore, the amount of diffusion through these holes will vary.
When water or a soap solution is brushed over the outside of an inflated tubeless tire, bubbles form.
Some vents may emit a continuous stream of bubbles. Others may produce intermittent bubbles. And
some may not bubble at all. This variety is normal and does not mean that there is anything wrong
with the tire. In fact, as long as a tubeless tire is inflated, there will be some diffusion from the vents.
When the loss rate exceeds 5% in 24 hours, recheck for possible injuries. Vents should remain open,
so check periodically to make sure they have not been covered over or closed by tire paint or spilled
solvent. And since vents may be covered during retreading, check for evidence that your retreads
have been revented.
Several basic characteristics of tubeless aircraft tires may be mistaken for problems:
1. Tire growth in the first 12 to 24 hours after inflation will result in a seemingly severe pressure drop.
Simply inflate, wait for another 24 hours, then check pressure. It will probably be within specs.
2. Make sure that initial inflation is to recommended operating pressure to ensure full tire growth.
3. It is normal for tubeless tires to show a small amount of pressure leakage throughout the life of the
tires.
Maintain tires at pressure specified in Chart 601, 6-00-00. When checking tire pressure, examine tires
for wear, cuts, bruises, and slippage. Apply Age-Master #1 to tires to protect against ozone attack and
weathering as follows:
1. Clean oil and grease from all tire surfaces.
2. Apply single heavy coat using brush at 0.4 - 0.5 fluid ounces per square foot. Cover surface
completely and evenly; allow to dry for 5 - 10 minutes.
3. Apply second coat per step 2; allow to dry for 20 - 30 minutes before handling.
4. Remove agent on wheel assembly with cleaning solvent.
5. Apply as conditions dictate.
Q. Hydraulic Power Pack
Check hydraulic power pack reservoir fluid level every 50 hours and fill as required. Special filling and
draining service hookup is installed inside right fuselage access panel of nose section. A pressure pot
or hydraulic test unit can be connected by removing panel, opening access in hydraulic component
covers and protective cap on suction; fill and drain fitting. Connect fluid supply line from supply source
to fitting. Raise lever to open valve and fill reservoir. To gravity fill reservoir, support hydraulic fluid
supply container higher than fluid level in power pack reservoir. Reservoir is full when fluid reaches full
line on transparent reservoirs. Be sure to close suction; fill and drain valve by placing lever in down
position before disconnecting supply line from fitting. Reinstall protective cap on fitting, close access
in hydraulic components cover, and install access panel.
EFFECTIVITY:
040-999
Jan 10/90
12-10-00
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