Revised: 2/18/94; Ground Procedure - Piper Navajo PA-31 Service Manual

PIPER NAVAJO SERVICE MANUAL
14-137. CONTROL VALVES. No service is recommended for these valves except for their replacement in
the event of failure.
14-138. TIMER. No field maintenance is recommended. Refer to Parts Catalog for replacement timer.
14-139. INSPECTIONS. A ground check of the entire deicer system should be made at least every 100 hours.
To permit ground checking the system without engine operation, a test plug is designed into all systems, usual-
ly between the pressure check valve and the combination unit.
Before checking the system, all deicers should be inspected for damaged areas and repaired according
to the procedure in this section outlining the cold patch or vulcanized repairs. In order to check the system,
refer to Table XIV-IX and Paragraph 14-140 for operating pressures and check procedures.
14-140. GROUND PROCEDURE.
NOTE
This operation may be omitted if the boots were installed on the
airplane subsequent to the last previous 100 hour check.
After the test pressure range is established, connect an external source of air providing this pressure to
the test plug. When the air supply is turned on, the check valves in the lines from the pneumatic pumps close
automatically. The deicer system should be within one psig of the recommended operating pressure with each
inflation cycle.
If deicers do not reach the operating pressure, check the inflation time to ascertain that the solenoid
valves are open the specified length of time (six seconds). If this is not the cause of trouble or if the boots
deflate slowly, the lines or valves may be plugged. Then the lines should be disconnected and blown clear.
Check the timing of the system through several complete cycles. All deicer boots should come ON for
six seconds. If the cycle time is off the specified time, determine and correct the difficulty.
Inflation must be rapid to provide efficient deicing. Deflation should be completed before the next
inflation cycle of the boots.
14-141. 100 HOUR INSPECTION. At each 100 hour inspection of the airplane, inspect and operate the deicer
boots. Make checks as follows:
a Carefully inspect the deicers for evidence of damage or deterioration and repair or replace dam-
aged boots.
b. Resurface boots which show signs of considerable wear or deterioration.
c. Inspect all hose connections which form a part of the pneumatic deicing system. Replace deterio-
rated sections of non-kink hose.
d. Check the operation of the boots and the operating pressure of the system as outlined in Paragraph
14-131 and Table XIV-IX.
e. If new or replacement boots have been installed, check the tube inflation to make sure that the air
connection stems have been properly connected.
f. Disconnect all drain lines in the system and check for proper drainage.
g. Check the on-off control switch for freedom of action. Check associated electric wiring.
h. Clean or replace the air filters.
14-142. REMOVAL OF BOOTS. The exact location of wing stall strips, as determined by the factory, is very
critical to the airplanes stall characteristics. Therefore, prior to removing deicer boots, determine exact loca-
tion of stall strips. Fabricate a template or determine exact vertical and horizontal location measurements from
a hard point on wing surface.
Revised: 2/18/94
ACCESSORIES AND UTILITIES
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