Fuel System Flashcards
Total capacity of tanks? Gals/lbs
1028 Gals, about 6900-7000 lbs
Why are fuel capacities different in each tank?
Fuel quantities in each tank are different due to the placement of the filler caps in each of the tanks.
How many fuel quantity probes and where are they located?
10
3 in each main tank and 1 in each aux tank.
How many fuel tank boost pumps?
8
2 in each main and 1 in each aux
Which tanks do the heater and apu run off of?
Heater runs off of right main and APU off of left main
How many gallons per minute can the pressure refueling accept and at what psi?
The pressure refueling system allows the helicopter to be completely refueled in about 4 minutes with fuel supplied at 300 Gallons Per Minute (GPM) at 55 PSI.
Where is the crossfeed fuel line located?
Located overhead at station 504 (x feed fuel shutoffs also located at station 504 )
What do the fuel tanks do in a crash?
The mounting bolts of the fuel cell shear off and allow the pods to separate from the aircraft .
Also, the fuel pod cell is self sealing.
Can the pilot tell if there is a hole in the fuel pod bladder?
If the self sealing chemical is inadvertently activated and not noticed by maintenance personnel, the pilot will not notice any change in fuel quantity due to the design of the fuel quantity indicating system.
What prevents fuel from spilling in the event of a rollover?
The tank venting system.
There are primary and alternate fuel vents. Where are they located
The primary vents are float/drain valve assemblies installed on the bottom aft end of each pod that also work to seal the drains in the case of a water landing.
The alternate fuel vents are the high vent pipes on the top of each tube (covered by the screen).
Will the vents prevent main tank over pressurization from over filling?
The vent system is NOT capable to keep up with the fuel pumps if the high level shutoff valves fail. This situation will result in main tank over-pressurization.
What PSI do the in tank boost pumps supply?
At least 22 psi
What are the functions of the main and aux boost pumps?
The main pumps provide positive fuel pressure to the engines. The aux pumps purpose is to transfer fuel to the main tanks.
The forward pumps in the main tanks are also used to evacuate the pressure refueling manifolds and crossover line through the operation of the jet pumps.
What is the purpose of the bell mouth fitting?
To draw fuel out of the main tank via the ENGINE driven fuel pump when the main tank fuel pump(s) fail.
What is the purpose of the jet pump?
To evacuate the fuel from the pressure refueling system using a Venturi type system (main tank boost pump pressure creates little vacuum to suck fuel out of line and spit it in main tank.
Are all fuel lines self sealing?
No-pressure refueling line is not self sealing.
What type of fuel probes are used?
Capacitance type. The capacitance changes as the fuel level in the tank changes.
What illuminates the fuel level lights?
When approximately 20% of fuel is remaining 320 to 420 Lbs, the thermistor control unit illuminates the ―L FUEL LVL‖ or ―R FUEL LVL‖ low caution lights.
Is there a physical connection between the fuel quantity indicator and fuel level probes?
No. They are Electrically connected to the cockpit fuel quantity indicator.
At what PSI do fuel pump lights come on?
10 PSI
Indicates that the pump has failed or the tank is empty.
What is the function of the (main) fuel pump relay and where are they located?
The function of each relay is to control application of AC power to the pumps.
Located in the cabin at station 340 on left and right sides.
How does electricity get from the boost pump switch on the control panel to the boost pump?
All of the boost pump relays are controlled by the fuel pump switches with 28 VDC. Each relay supplies its respective pump with 115 VAC, three phase, for operation.
How are the auxiliary boost pumps relays different?
The auxiliary pump relays are controlled by thermistor control units, mounted externally on the top of each (main boost pump) relay box, and two thermistors mounted on each auxiliary pump mounting bracket.
When an auxiliary tank empties, and the thermistors on that pump mounting bracket become uncovered, DC power is interrupted to the pump relay through the thermistor control unit. This in turn removes AC power from the pump. In order for the pump to turn on again, fuel must cover both thermistors on the pump mount bracket
Where are the fuel pressure switches, which light the caution panel, located?
Aux switches are in aft inner tank area (fuel on way to main tank) and main switches are on the manifolds with the engine and crossfeed fuel valves.
What are fuel check valve function?
Prevent reverse flow from engine, prevent fuel from transferring to opposite tank when crossfeed is open and fuel pumps are off. Also the check valve incorporates a thermal relief that allows fuel to empty back into tank via bell mouth fitting during static times when fuel might expand (to prevent burst lines).
What is the fuel quantity indicator switch box for? Where is it located?
Fuel quantity electrical signals from six probes are connected to the switch box.
(a) If the refuel station switch on the overhead panel and the refuel panel power switch are OFF, the signals are connected to the cockpit fuel quantity selector switch.
(b) When the cockpit and refuel station switches are ON, 28 VDC is connected to the switch box and operates the relays.
(c) This connects the electrical fuel quantity signal to the refuel station selector switch.
Located station 232 overhead
Why does left side carry more fuel?
It carries more fuel if done via over wing filling due to where the fill port is and the angle the aircraft sits. The left side Carrie’s approximately 4 more gals in this case.
Can you use 100LL fuel?
Yes, but the limitation is “not to exceed 6 hours”
Which of the 3 fuel probes in the main tank sends the total to the cockpit? Which probe is quantity of tank sent from?
Forward probe. Quantity from center probe.
The fuel quantity indicator receives both digital and analog signals. Which signal is which?
Total fuel is digital
Analog is for each tank idv.
Where do the boost pumps pressurize fuel?
In the line.
What reduces vibrations to and from fuel tanks?
Vibration isolators
Why do the fuel cells need to be vented?
Because they are bladders and therefore collapsible.
Where do the fuel cells mainly vent from?
From the bottom of the tank. Secondarily from the top.
When does the fuel low light come on and why is it a variable number?
320-420 lbs. variable because thermistor that sits on probe is adjustable, so not always perfect, but within a range.
What processes the fuel signals and sends them to the cockpit?
Fuel pump relay box.
Why does the AUX boost pump have 2 switches?
Because the fuel acts as a coolant to the pump, they needed a separation of the switches so sloshing fuel wouldn’t be turning on and off the pumps. Both switches need to be covered by fuel for the unit to turn on.
What much each thermistor have?
A thermistor control unit that acts as a brain to open and close relays to turn components/lights off and on
Where are the main tank fuel pressure switches located? Aux tanks? What do these turn on/off?
Main tank pressure switches are located on the manifold with the crossfeed and engine fuel valves. Aux tank pressure switches are located in the inner-tank areas (can’t see aft). Main tank switches turn master caution L/R fuel pressure light on. Aux switch turns aux pump light on (overhead panel). Lights come on at 10 psi or less. Pressure for the AUX switch is sensed in the line leading to the main tank.
How many thermistor control units are there?
3: 2 for L/R aux pumps, 1 for low fuel level warning light system.
Refuel station switch provides power to what?
Provides power to refuel station panel AND closes refuel gate valves in aft inner tank areas when OFF. IF LEFT ON, FUEL WILL JUST RECIRCULATE IN AFT TANKS.
What is a good way to remember fuel carried per side of the helicopter?
275g/1800 lbs (mains)
120g/800 lbs (aux)
Remember, we carry about 6800 lbs (about 1000 gals), so each side is about 3400-3500lbs.
What are the fuel line check valves inside the helicopter for?
To prevent reverse flow from engine when supply is greater than demand, prevent transfer of fuel during crossfeeding operations, and prevents air from being drawn into line if boost pump fails.
When the Fuel LVL light comes on, what is being measured?
It only takes into consideration what is left in the main tanks. When 20% of the quantity in the main tanks is left, the light will come on.
