Checking Landing Gear Cycle Time; Checking Time Delay Valve - Piper Cheyenne IIIA Airplane Maintenance Manual

PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. Main (continued)
5. Cycling Landing Gear. (continued)
(f) After completion of cycling, ensure landing gear selector handle is in DOWN, neutral position,
and landing gear is down and locked.
(g) Disconnect hydraulic test unit.
(h) Remove airplane from jacks (refer to 7-10-00).
6. Checking Landing Gear Cycle Time.
NOTE: The following times, taken using a single test unit, can be considerably reduced by using
two test units, one hooked to each firewall fitting. If times are within limits when operated
by test unit, but exceed limits when operated by engine driven pump, either internal
leakage in pump or suction air leak through suction plumbing system to either of the
engine driven pumps could exist. (Refer to paragraph entitled Checking For Suction Air
Leakage.) If tests indicate a defective pump, repair or replace defective pump. If time
exceeds limit when operated by either test unit or engine driven pump, internal leakage
exists in hydraulic system. Check actuators for internal leakage and repair or replace
actuators as required. If actuators are not defective, power pack internal leakage exists,
and repair or replace power pack.
When malfunction in hydraulic system is suspected, due to slow gear cycle time, it could be
caused by low fluid in airplane reservoir causing system to be full of air. The following procedure
will purge air from system and fill reservoir:
(a) Place airplane on jacks (refer to 7-10-00).
(b) Cycle landing gear through two complete cycles.
(c) Excessive foam in reservoir indicates a possible leak in suction plumbing where air is drawn
into system. Check all ground service suction connections for leaks.
(d) With landing gear extended, place gear handle in full UP position, and record time required for
gear to retract and doors to close. Time must not exceed 9 ± 0.5 seconds, plus time required
for time delay valve to operate.
(e) With landing gear retracted, place gear handle in full DOWN position, and record time required
for gear to extend and doors to close. Time must not exceed 8 ± 0.5 seconds, plus time
required for time delay valve to operate.
7. Checking Time Delay Valve.
(a) Connect hydraulic test unit (described in Connecting Test Unit).
(b) With test unit operational and airplane master switch ON, move landing gear selector handle to
DOWN position. Note delay of handle returning to NEUTRAL position.
NOTE: Time delay between moving selector handle to down position (with master switch on)
and automatic releasing of selector handle to neutral, must be 3 to 9 seconds at room
temperature. Colder temperature causes a longer delay.
(c) If time delay is not 3 to 9 seconds, ensure valve is not air locked. Bleed air out by holding
selector down for 30 seconds and complete three or four rapid movements from neutral to
down.
(d) Replace time delay valve, if defective.
(e) Disconnect hydraulic test unit.
EFFECTIVITY:
040-999 PAGE 5
29-10-00
Jan 10/90