(c)
Starttestunit pump motor.
(d)
Placegearselectorhandlein UP or DOWN position. Slowlyclosebypass valve untilsystem pressurehasreachedthat specifiedin 29-00-00, Chart 2.
(e)
Operate gear using landing gear control handle.
NOTE: If retraction malfunctiondue to air in system is expected, followprocedurefor CheckingLandingGear Cycle Time. Gearcyclingtimecan be prolonged by slowly openingthe test unit bypassvalve part way and bleeding off part of pump flow.
EFFECTIVITY:
PAGE4 29-10-00
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PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL
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)
Disconnecthydraulic 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)
Withlanding 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 causesa 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)
Disconnecthydraulictest unit.
EFFECTIVITY: 040-999 PAGE5
29-10-00Jan 10/90
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. Main (continued)
8. CheckingHandleReleaseto Neutral.
NOTE: Onereleasevalvereleases handle from bothgear down and gear up positions. If handle returnspringsare adjustedproperly,releasevalvemustrelease handle fromboth positionsat same pressure. The following procedures checkreleasepressurefrom gear downpositionand release pressure fromgearup position. This is done to assure satisfactoryoperationof other equipmentrelative to handle releaseoperations.
(a)
Placeairplaneon jacks(referto 7-10-00).
(b)
Connecthydraulictest unit (described in Connecting TestUnit).
(c)
Run landing gear through twocompletecycles,ending with gear down and lockedanddoors closed.
(d)
Set hydraulic test unit bypassvalvefully open.
(e)
Place landing gear selector handlefully down.
(f)
Closebypassvalveveryslowly until handletripsbackto neutral. Ensuregaugepressurereadingscomplywith those in 29-00-00,Chart2 when handletrips to neutral. Allowtimefor time delay valveto open.
(g) 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：夏延飞机维护手册 Cheyenne IIIA PA-42-720 AMM 1(148)
