PIPER AIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL
A. Distribution(continued)
17. Jet Pump Flow Check
WARNING: AREA SURROUNDING AND INSIDE OF AIRCRAFT MUST BE WELL VENTILATEDANDCLEAR OF ANY SOURCE OF FLAME OR SPARK.
(a)
Drain affected fuel system (if not already drained).
(b)
Disconnect and plug jet pump return line from pump.
(c)
When accumulating any fuel, ensure it is done outside or as close as possible to outside of aircraft. Obtain an eight foot or longer piece of 1/2-inch hoseor tubing. Connect line to jet pump, and while keeping free end 24 inches above jet pump outlet, route line out or near door. Connect control on/off valve to free end of line.
(d)
Withfirewall shutoff valve closed (off), add at least 20 gallons of fuel to system.
(e)
Open firewall shutoff valve, operate boost pump until fuel flow clears, and close control valve to checkfor leaks. With control valve open, it must take maximum 4.3 minutes to accumulate 5 gallons(466PPH minimum).
18. Cleaningof Fuel Filter Screen
(a)
Clean bowl and body with oil solvent and check for damage. Replace if necessary.
(b)
Cleanfilter electrosonically and inspect damage. Replaceif necessary.
EFFECTIVITY: 040-999
PAGE14 28-20-00
Jan 10/9028-20-00
PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL
A. Indicating
1. DescriptionandOperation
(a) Fuel Quantity IndicatingSystem
The fuel quantity indicatingsystem contains two separate capacitancesystemsusing dual
display indicators.Eachidenticalprobe system measuresits fuel capacitywith two probes
in each inboardmaincell (95 gal cap.), and one probe in all other cells and tanks (refer to
28-40-00 Figure 1). The probeunits have fixed tabularcapacitorelementsto match the
contourof the respective cell or tank position. This system displays very accurate
indicationsdue to the linear response of probes. With fixed electrodes,sensor capacitance
is about 2:1, or approximately twice as great with a full system. Any change in fuel quantity
betweenfull and empty producescorrespondingchanges in capacitance. These changes
areamplified within the dual indicator andcontinuouslydisplayedon the indicatorface. The
dual indicator readoutis a direct indication of fuel weight on board the aircraft.
Thedual-needlefuelquantityindicator,mountedonthe copilot side abovethe control wheel, has its own ac inverterto powerthe capacitance probesystems. Electricalpower for the entire system is supplied fromthe 28 Vdc aircraft power supply.
(b) AutomaticFuel Pump System(referto 28-10-00in PA-42-720 (AdvancedTrainer)Wiring DiagramManual)
Theautomaticfuel pump system suppliesthe appropriatesystemwith properfuelif fuel pressurefalls belowan acceptable level. If fuel pressure startsto fall, the fuel pressuregauge mechanismsensesthe drop, and at 15 psi, completes a circuit to activate the low fuel pressure annunciatorandthe fuel pumprelay. The relay completesa circuitbetweenthe autoposition of the fuel pump switch andthe fuel pump.
Thissystemonlyworkswith the switchin auto,which in turn prevents the submergedfuel pumpfrom runningcontinuously.Theannunciatorlight will still come on at 15 psi. With both
the pump and lightcontrolled,in this case bythe gauge,the gauge also shutsthemoff when pressurerises above 33 psi.
Thefuel pump relaysarelocatedon a shelf mountedto bulkheadat Fuselage Station25.6. Accessto the shelf is made by removing the royalite coverat the rear of the nose baggage compartment.
EFFECTIVITY:
040-999 28-40-00 PAGE
Jan10/90
PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL
A. Indicating (continued)
Outboard
MainTank
FuelCapacitanceProbeInstallations
Figure 1
EFFECTIVITY:
040-999
28-40-00Jan 10/90
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL
A. Indicating
2. FaultIsolation-Fuel System
Fault
Fuel gauge failsto indicate proper tank level.
Lowfuel pressure.
Engine stops with more than 10 gallons (67lbs.) of fuel remainingand/or a significant amount of fuelstill remainsin aft inboard(aux) tank.
Erraticmovementof
meter in Fuel Quantity
Indicator.
FuelQuantity Indicator
inoperative.
CHART 1 FAULTISOLATION(FUELSYSTEM)
Cause
Circuit breaker out.
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