United States Army Aviation Warfighting Center
Fort Rucker, Alabama
January 2008
UH-60A
STUDENT HANDOUT
UH-60A FUEL SYSTEM
4744-3
PROPONENT FOR THIS STUDENT HANDOUT IS:
110TH AVIATION BRIGADE
ATTN: ATZQ-ATB-AD-C
Fort Rucker, Alabama 36362-5000
FD5: This product/publication has been reviewed by the product developers in coordination with the USAAWC,
Foreign Disclosure Officer, Fort Rucker, AL. foreign disclosure authority. This product is releasable to students
from all requesting foreign countries without restrictions.
TERMINAL LEARNING OBJECTIVE
ACTION: State the characteristics of the UH-60 fuel system.
CONDITIONS: Without references, given the Aircraft Systems Test and an answer sheet.
STANDARDS: Describe the UH-60 fuel system, to include the APU fuel system. Describe the location,
function and interaction of components associated with the UH-60 fuel system.
SAFETY REQUIREMENTS: None.
RISK ASSESSMENT LEVEL: Low
ENVIRONMENTAL CONSIDERATIONS: There are no environmental concerns for this lesson.
EVALUATION: You must answer four out of six questions correctly to receive a "GO" on this scoreable
unit.
LEARNING STEP/ACTIVITY 1: Identify the characteristics of the UH-60 Fuel System.
a. UH-60 Fuel System description. The fuel system supplies fuel to both engines and the APU. The fuel
system consists of two interchangeable, crashworthy, self-sealing fuel cells; self-sealing supply lines;
quantity gauging and low level warning systems.
b. Fuel Cells
(1) The cells are located on the left and right side of the transition section.
(2) Cells are constructed of several layers to make them crashworthy and ballistic tolerant.
These layers are the inner liner, nylon fuel barrier, sealant, and retainer.
(3) The fuel cells are constructed of several layers of a rubber compound with a nylon filament added
for strength, and an outer coat of vithane to give the cell a scuff resistant exterior.
(4) The fuel cell materials will allow the projectile to enter or leave the cell, and then the materials will
return to their original position. This mechanical reaction is almost instantaneous. The chemical reaction
takes place as soon as fuel vapors penetrate through the inner liner material and reach the sealant. The
sealant, upon contact with fuel vapors, will extend or swell to several times its normal size. This
effectively closes the rupture and prevents the fuel from escaping. The sealant is made from natural gum
rubber.
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(a) The sealer mixes with the fuel to seal the fuel cell.
(b) It will automatically seal a bullet hole from a 7.62 millimeter (mm) armor piercing projectile.
(c) A water filled fuel cell has been dropped from 65 feet with no damage.
(5) Gravity Drain Valve
(a) The gravity drain valves are centrally located under the transition section below each cell
which provides a means of draining fuel from each fuel cell.
(b) The drain valve is located in a self-sealing compartment.
(c) The access door seal consists of the same chemical compound as in the fuel tanks.
(d) This special compound will automatically seal the compartment should a leak occur at the
drain valve.
(6) Unusable fuel is approximately .435 of a gallon.
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c. Servicing. The UH-60 fuel system can be serviced by one of three methods.
(1) Gravity Refueling Port
A standard Army-type filler cap is located on the right and left sides of the transition section allowing for
individual tank gravity fueling. Maximum capacity is 180 gallons.
(2) Pressure Refueling Port
(a) Pressure refueling or defueling of the helicopter is accomplished through a single-point
service connection (standard 5 inch NATO fitting) on the left side of the aircraft.
(b) The right fuel cell is pressure filled through an interconnect tube from the left fuel cell.
(c) This interconnect tube does not interconnect the fuel cells for the supply system.
(d) When using the single-point pressure refueling method, the fuel cell's usable capacity is
approximately 179.5 gallons.
(e) Maximum fuel pressure from the service vehicle is 55 psi, at 300 gpm.
(f) The following valves are used for both pressure and closed circuit fueling and defueling:
1. Pressure Fuel/Defuel Valve
a. The pressure fuel/defuel valve is a double-diaphragm (primary and secondary
chambers), spring-pressure-operated valve.
b. It is controlled by either incoming fuel pressure or back pressure (high-level, float-type,
shutoff valves) acting on the backside of the diaphragm.
2. High-Level Shutoff Valve/Tank Full Shutoff Valve
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a. Each fuel cell has two high-level shutoff valves.
b. The fuel level activates these float-type valves.
c. The high-level shutoff valve closes the pressure refueling valve in the tank when the
tank is full.
3. Low-Level Shutoff Valve
a. A low-level shutoff valve is located in the bottom of each fuel cell.
b. During pressure defueling a low-level shutoff valve closes the pressure refueling valve
when the tank is empty.
(3) Closed Circuit Refueling Port
(a) A single-point service connection (standard 2.5-inch fitting) is located on the left side of the
aircraft for closed circuit fueling.
(b) The inlet pressure rate is 15 psi, and the flow rate is 110 GPM.
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(c) When using the closed circuit refueling method, the fuel cell's useable capacity is 178 gallons.
(4) Refueling Operation
(a) When the fuel reaches the high level shut-off valves, the float raises and closes the check
valve.
(b) The back pressure of fuel increases in the respective chamber of the fueling/defueling valve,
terminating the refuel process.
(c) The refueling process is the same for both pressure and closed circuit refueling.
(5) Pressure Defueling
(a) Pressure defueling is the preferred method for defueling the aircraft.
(b) Suction pressure should not exceed 3 psi.
(c) During pressure defueling of the aircraft, the low-level shutoff valve allows air pressure to the
refuel/defuel valve.
(d) After pressure defueling approximately 3.5 gallons of fuel remains in the fuel cells. The
gravity drains under the aircraft are used to remove this fuel.
d. Fuel Quantity System
(1) The fuel quantity indicating system is a capacitance-type system that visually indicates the
amount of fuel, in pounds, in each cell.
(2) This system requires 115 Volts of Alternating Current (V ac) for cockpit indications.
(3) A fuel quantity probe is located inside of each cell, sensing the level of fuel.
(4) The signal is amplified, conditioned, and routed through the appropriate SDC to the fuel quantity
indicator.
(5) The fuel quantity indicator is located on the Central Display Unit.
(a) The fuel quantity vertical indicator displays fuel quantity in LBS X 100 for both the # 1 and # 2
fuel tanks.
(b) The FUEL QTY indicator scales are amber for 0 to 200 pounds of fuel, and green for 200 to
1500 pounds of fuel.
(c) A digital readout of total fuel in both tanks is shown at the bottom of the vertical indicators.
(6) A fuel quantity indicator test switch is located on the miscellaneous switch panel. The switch is a
press-to-test switch that is used to test the fuel quantity system.
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(a) The fuel quantity system can be checked by pressing the FUEL IND TEST push-button on
the miscellaneous switch panel. Test indications should be the following:
1. Both vertical scales of the FUEL QTY indicator should change.
2. The digital readout should change.
3. The #1 and #2 FUEL LOW cautions should flash in unison with the MASTER CAUTIONS.
(b) Electrical power required for fuel probe and low level sensor operation of the fuel quantity
system test circuit is 28 V dc, supplied by the # 1 dc primary bus.
e. The fuel low-level warning system consists of one low-level sensor on each fuel quantity probe, a lowlevel warning conditioner, #1 FUEL LOW and #2 FUEL LOW cautions, and a fuel low indicator test circuit.
(1) The low-level sensor called a thermistor is located on the lower end of each fuel probe. It senses
the presence or absence of fuel in each tank at a specific level.
(2) When approximately 172 pounds of fuel remain in the fuel cell, a #1 FUEL LOW or #2 FUEL LOW
caution will flash in unison with the MASTER CAUTIONS.
(3) The appearance of these cautions does not mean a fixed time period remains before fuel
exhaustion, but is an indication that a low fuel condition exists.
(4) The pilot can reset the master cautions; however, the #1 or #2 FUEL LOW cautions will continue
to flash.
f. A fuel cell vent system utilizes a 2.5 inch vent line, located on the top of each fuel cell.
(1) They connect over the aft transition section through a common vent line that exits underneath the
aircraft.
(2) If the helicopter banks and/or rolls excessively, or should the aircraft lay on its side, the valves will
prevent fuel from flowing out of the vent line onto the ground.
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(3) The vent line provides positive atmospheric pressure inside the fuel cell.
(4) The vent valves have double-acting check valves which open when there is a pressure differential
between the fuel cells and the atmosphere.
(5) Check valves are located on top of the fuel cell, inside each vent valve.
(6) These valves prevent the fuel cell from becoming over pressurized by allowing air to escape
through the vent, when the tanks are being refueled under pressure.
(7) Each cell vent line is equipped with self-sealing breakaway valves preventing fuel loss should a
break occur in the line.
g. Fuel sample guide tubes provide a means for quality fuel sampling in each tank.
(1) The tubes are made of a 0.5 inch plastic conduit, located near the opening of each gravity
refueling port.
(2) They extend towards the bottom of each fuel cell.
(3) A thumb operated hand pump is utilized to draw fuel form the bottom of the cells.
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LEARNING STEP/ACTIVITY 2: Identify and/or describe the operational characteristics of the fuel system
components of the UH-60.
a. Fuel Supply Lines
(1) The # 1 fuel cell has two main fuel supply lines, one for the # 1 engine and one for the Auxiliary
Power Unit (APU).
(2) The # 2 fuel cell has one main supply line for the # 2 engine.
(3) The #1 and #2 main supply lines are self sealing.
(4) Check valves located on the pickup end of the main engine supply line maintains primed fuel to
the supply line and prevents a reverse flow of primed fuel into the main fuel cell.
(5) The supply line thermal bypass check valve is located parallel to the outlet check valve and
relieves excess pressure in the supply line due to thermal buildup.
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b. Breakaway Valves
(1) There are 15 breakaway valves located throughout the fuel system.
(2) These valves provide an automatic seal to prevent loss of fuel and reduce the possibility of fire, if
the valves break away from the fuel lines during a crash or malfunction.
c. Submerged Fuel Boost Pump
(1) Each fuel cell contains an electrically operated submerged fuel boost pump.
(2) The fuel boost pumps provide pressurized fuel in the main fuel supply lines to the engine driven
fuel pumps.
(3) Each boost pump operates on 3 phase, 115 V ac at 25-27psi outlet pressure.
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(4) Each boost pump is controlled by a two-position switch on the FUEL BOOST PUMP CONTROL
panel; the switches are marked ON and OFF.
(5) Each boost pump in monitored by a pressure switch which signals proper pressure output from
the pumps.
(6) The green advisory light, near each control switch on the panel, receives 28 V dc from the battery
bus indicating proper pump pressure and operation.
d. Main Fuel Selector Valve
(1) There is a fuel selector valve for each engine, which is located on the airframe side of each
engine firewall.
(2) The fuel selector valve is connected to the ENG FUEL SYS selector lever on the engine control
quadrant by push/pull cables to provide a direct feed or cross feed of fuel to the engines.
(3) The three positions of the fuel selector valves are OFF, DIR (direct), and XFD (cross feed).
(a) OFF shuts off fuel flow to the engine.
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(b) DIR allows fuel to flow directly from its individual fuel cell to the engine.
(c) XFD allows an engine to receive fuel from the opposite fuel cell (#1 engine from #2 fuel cell).
e. ENG FUEL SYS selector levers
(1) There are three ENG FUEL SYS selector lever positions on the quadrant: OFF, DIR and XFD.
(2) When the ENG FUEL SYS selector lever is moved to the desired position, a cable routed through
the airframe to the valve will position the valve in the desired position.
(a) OFF shuts off fuel flow to the engine.
(b) DIR allows fuel to flow directly from its individual fuel cell to the engine.
(c) XFD allows an engine to receive fuel from the opposite fuel cell (#1 engine from #2 fuel cell).
LEARNING STEP/ACTIVITY 3: Identify and/or describe the operational characteristics of the engine fuel
system of the UH-60.
a. Engine Driven Boost Pump
(1) The engine driven boost pump is located on the front left side of each engine accessory module.
(2) The pump's inlet side creates a negative pressure -3 to -6, which suctions fuel from the fuel cell
up to the pump and is driven by Ng in proportion to Ng speeds.
(3) This prevents fuel from leaking or spraying out (possibly feeding a fire) should the line be
damaged or ruptured.
(4) The pump's outlet side creates a positive pressure 45-90, which pumps fuel to the HMU.
(5) A fuel pressure switch, which is located on the output side of each pump, monitors pump output
and illuminates the fuel pressure caution if fuel pressure drops below 9 psi.
b. Fuel Filter Assembly Components
(1) The fuel filter assembly is located on the left front of each engine accessory module.
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(2) The fuel filter provides filtration for engine fuel prior to entering the (HMU).
(3) The fuel filter assembly consists of the filter head, filter bowl, a disposable filter element,
impending bypass indicator button, a bypass relief valve, and a filter bypass pressure switch.
(4) The filter element is a 30-micron pleated barrier type filter element.
(5) The impending bypass indicator button indicates condition of the filter and pops at 8-10 psid.
(6) The filter bypass pressure switch, located on the output side of each filter, monitors the condition
of the filter.
(7) A bypass valve allows fuel to bypass when the filter becomes clogged.
(8) The filter should go into a bypass condition at 18-22 psid, illuminating the #1 FUEL FLTR
BYPASS or #2 FUEL FLTR BYPASS cautions in the cockpit.
c. Hydromechanical Unit
(1) The HMU is mounted to and driven by the AGB, and contains a high pressure pump that delivers
fuel to the POU.
(2) The nine functions of the HMU are:
(a) High Pressure Fuel Pumping
(b) Fuel Flow Metering
(c) Collective Pitch Compensation through the LDS
(d) Acceleration/Deceleration Flow Limiting
(e) Ng Limiting
(f) Variable Geometry Positioning
(g) ECU Lockout via the PAS
(h) Torque Motor Servo to Trim Ng Output
(i) Opens Vapor Vent for HMU Priming
(3) Refer to the engine handout for a detailed description.
d. Oil Cooler
(1) The cooler is mounted adjacent to the fuel boost pump on the forward side of the gearbox.
(2) Fuel is used as the coolant and is provided to the cooler via the boost pump, fuel filter, and HMU.
(3) Fuel flows through the tubes, while the oil flows over the tubes, resulting in the counter-parallel
flow arrangement.
e. Pressurizing and Overspeed Unit
(1) The POU has four functions.
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(a) Sequences start fuel.
(b) Sequences main fuel.
(c) Purges start and main fuel manifolds and nozzles/injectors.
(d) Fuel flow cut back to provide Np O/S protection.
(2) Refer to the engine handout for a detailed description.
f. Engine Manifolds
(1) The start fuel manifold carries starting fuel from the sequence valve to the two start fuel nozzles,
located at the 4- and 8-o'clock positions in the combustion chamber.
(2) The main fuel manifold carries fuel from the sequence valve to the 12 main fuel injectors located
in the combustion chamber.
(3) The manifold also carries compressor discharge (P3) air for purging the start and main fuel
nozzles after fuel is shut off to them. This prevents coking of the nozzles.
g. Engine Fuel Prime System
(1) The engine fuel prime system provides a means of priming the engine's HMU if required.
(2) It provides 5psi of fuel pressure to the APU fuel control and primes the APU fuel lines for APU
operations.
(a) Prime/Boost Pump
1. The prime/boost pump is located on top of and between the # 1 and #2 fuel cells. It is
used to prime the engine and APU fuel lines, and provide fuel under boost pressure for APU operation at
high altitudes.
2. The pump is a 28 V dc, wet-motor, vane-type pump with an output of 5psi, which provides
a means of priming both engines and the APU.
(b) Prime/Boost Pump Control Switch
1. The Prime/Boost Pump control switch is located on the upper console on the Overhead
Control panel marked FUEL PUMP, FUEL PRIME, OFF, and APU BOOST.
2. When the Prime/Boost Pump control switch is moved to the FUEL PRIME (spring loaded)
position, it energizes the prime/boost pump and opens all three shut-off valves. This position can be used
to prime the engines and APU.
3. The APU BOOST position is used anytime the APU is running. This turns on the prime
boost pump and opens the APU shut-off valve.
4. The OFF position turns the pump off.
(c) Engine Prime Shutoff Valve
1. There are two engine prime shutoff valves, one for each engine.
2. The valves are located on the top of each cell, attached to the main fuel breakaway valve.
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3. The # 1 or # 2 engine starter system will electrically open or close the prime shutoff valves
and supply electrical power to the prime boost pump from the 28 V dc battery bus. Referred to as AutoPrime.
4. The valves are also controlled by the fuel pump switch.
5. When the starter speed switch drops out, the prime shutoff valve closes and turns off the
prime boost pump if the fuel pump switch is in the OFF position.
6. When the valve closes, the engine driven boost pump takes over.
(d) Engine Prime Procedures (for alternate method see Section IV FUEL SYSTEM in TM 1-1520237-10)
1. When priming the fuel system for the engine, using the submerged boost pumps, a/c
power must be available.
2. ENG POWER CONT lever(s) - Hold at LOCKOUT.
3. FUEL BOOST PUMP CONTROL switch(es) - ON until crewmember reports fuel
from the overflow drain (steady stream).
4. FUEL BOOST PUMP CONTROL switch(es) - OFF.
5. ENG POWER CONT lever(s) - OFF.
h. Cautions/Advisories
(1) #1 FUEL PRESS - The #1 FUEL PRESS caution indicates that the left engine fuel pressure
between engine-driven fuel pump and the HMU is below 9 psi.
(2) #1 FUEL FLTR BYPASS - The left engine fuel filter has excessive pressure differential across
filter and filter is in a bypass condition.
(3) #2 FUEL PRESS - The #2 FUEL PRESS caution indicates that the right engine fuel pressure
between engine-driven fuel pump and the HMU is below 9 psi.
(4) #2 FLTR BYPASS - The right engine fuel filter has excessive pressure differential across filter
and filter is in a bypass condition.
(5) PRIME BOOST PUMP ON - Whenever the Prime boost pump switch is in PRIME or APU
BOOST position, or during a start cycle, the PRIME BOOST PUMP ON advisory will appear.
i. Engine Start Fuel Flow
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(1) The engine driven boost pump suctions fuel at -3 to -6 psi from the selected fuel cell.
(2) If the electric submerged boost pump is "ON", fuel is pumped to the engine driven boost pump in
the pressurized mode.
(3) The engine driven boost pump raises the output fuel pressure to 45-90 psi, and pressurizes the
AGB fuel passages.
(4) Next are the fuel filter, the fuel pressure sensor (controls the #1 FUEL PRESS and #2 FUEL
PRESS cautions), the fuel filter, and the HMU.
(5) The HMU has a high pressure vane pump that increases the fuel pressure to 300psi at idle, and
varies the fuel pressure from 400-832psi at fly.
(6) Main metered fuel then flows from the HMU through the oil cooler, the POU, and then to either 2
start fuel nozzles or 12 main fuel injectors.
LEARNING STEP/ACTIVITY 4: Identify and/or describe the operational characteristics of the APU fuel
system of the UH-60.
a. APU Fuel System
(1) The APU fuel supply line, located on top and between the # 1 and #2 fuel cells, supplies fuel from
the # 1 fuel cell to the APU fuel control for APU operation.
(a) The major difference between this fuel system and the main engine fuel system is that the
APU fuel supply line is not self-sealing.
(b) A breakaway valve is also located in the APU supply line.
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(2) APU Supply Line Check Valve
(a) The APU supply line check valve is located on the pickup end of the APU supply line inside
the # 1 fuel cell.
(b) The check valve maintains a supply of primed fuel to the supply line.
(3) The supply line thermal bypass check valve is located parallel to the outlet check valve and
relieves excess pressure in the supply line due to thermal buildup.
(4) APU Fuel Operation
(a) The prime/boost pump, located above the # 1 fuel cell, is used to prime the engine and APU
fuel lines, and provide fuel under boost pressure, for APU operation at high altitudes.
(b) Placing the fuel pump switch in the APU BOOST position energizes the prime boost pump
and the associated PRIME BOOST PUMP ON advisory.
(c) When the fuel pump switch is in the APU BOOST position, the Prime Boost pump shutoff
valve will open and route fuel to the APU fuel filters.
(d) The fuel is directed to the APU fuel pump, located inside the fuel control enclosure, which
provides high-pressure fuel to be metered for the APU.
(e) When the FUEL BOOST PUMP switch is in the off position the PRIME BOOST PUMP ON
advisory will disappear.
LEARNING STEP/ACTIVITY 5: Identify and/or describe the emergency procedures for malfunctions of
the UH-60 fuel system.
a. #1 or #2 FUEL PRESS Caution Appears.
(1) If the caution appears, flameout is possible. Do not make rapid collective movements. This
emergency procedure has been written to include corrective action for critical situations. Critical
situations are those where the loss of an engine represents a greater hazard than the possibility of
pressurizing a fuel leak.
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(a) If the caution appears and the situation is critical:
1. FUEL BOOST PUMP CONTROL switches - # 1 PUMP and # 2 PUMP - ON.
2. LAND AS SOON AS PRACTICABLE.
(2) This portion of the emergency procedure has been written to provide the best method of isolating
the cause of the failure and prescribing the proper corrective action when the situation is not critical. This
portion of the emergency procedure assumes the FUEL BOOST PUMP CONTROL switches are OFF
when the malfunction occurs.
(a) If the situation is not critical:
1. ENG FUEL SYS selector on affected engine - XFD.
If caution still appears:
2. FUEL BOOST PUMP CONTROL switches - # 1 PUMP and # 2 PUMP - ON.
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If caution still appears:
3. FUEL BOOST PUMP CONTROL switches - # 1 PUMP and # 2 PUMP - OFF.
4. LAND AS SOON AS PRACTICABLE.
b. #1 and #2 FUEL PRESS or #1 and #2 FUEL FLTR BYPASS Cautions Appear
1. LAND AS SOON AS POSSIBLE.
c.
#1 or #2 FUEL FILTER BYPASS Caution Appears
1. ENG FUEL SYS selector on affected engine - XFD.
2. LAND AS SOON AS PRACTICABLE.
d. #1 and #2 FUEL LOW Cautions Appear
1. LAND AS SOON AS PRACTICABLE.
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