ata 73

ATA CHAPTER 73

ENGINE FUEL AND CONTROL

73-10 DISTRIBUTION

2

OPERATION ... 2

Fuel System ... 2

Fuel Filter/Heater Unit ... 4

Fuel Manifold Assy & Nozzles... 7

Fuel Drain Ejector Tank... 8

OPERATION ... 8

73-20 CONTROLLING

9

Hmu Eec Mode... 10

Hmu Manual Mode ... 12

Fault Detection System ... 13

EEC Features & TSC Features... 15

EEC SAFETY FEATURES ... 15

TSC FEATURES ... 15

Auto-Feather System... 16

NH Overspeed Test: ... 18

Engine Trim:... 18

73-30 INDICATING

19

FUNCTIONAL DESCRIPTION ... 19

OPERATION ... 19

Fuel Flow Primary EICAS Page ... 21

FUEL FILTER / PRESSURE... 22

FUNCTIONAL DESCRIPTION ... 22

OPERATION ... 22

Fuel -Flow / -Used / -Temperature / -Pressure and HP Filter on Fuel Page ... 23

Fuel Flow on Engine Page... 24

LP Fuel Filter on System Maintenance Page ... 25

Fuel Flow on RMU Page 2... 26

INDEX

27

73-10 DISTRIBUTION

OPERATION

Fuel System

Fig. 1 Fuel System

Fuel is pumped from the aircraft fuel tanks, to the engine fuel inlet, by either the electrical fuel booster pumps or by the ejector pumps. Fuel is introduced into the engine fuel system at the fuel heater unit. This unit consists of a filter and a fin type heater in two integral housings. The filter housing contains a bypass valve to ensure an adequate fuel flow in the event of blockage and an indicator to wam of impending blockage.

The heater housing is divided into two circuits. RGB lubricating oil flows through one circuit to transfer heat to the fuel, which flows through the other circuit. A themnal sensor in the fuel circuit operates a valve to regulate the oil flow in order to maintain proper fuel temperature. The outlet port incorporates a switch to operate a low pressure waming and a retum port for the fuel drain tank. Fuel transfers to the fuel pump by an extemal transfer tube.

The pump is a positive displacement type. The inlet contains a screen which, when blocked, lifts from it's seat to allow the fuel to bypass. The fuel passes through the inlet screen and is pumped through the outlet filter by a single stage gear type pump. The outlet filter has a bypass valve to divert the fuel flow in the event of filter blockage and an indicator to wam of impending blockage.

To maintain fuel inlet pressure, an amount of fuel is retumed from the HMU to the inlet side of the pump through an ejector nozzle positioned ahead of the main inlet.

Fuel is routed between the HMU and the pump by intemal passages which are sealed by prefommed packings.

The hydromechanical metering unit (HMU) divides the high pressure fuel between the motive flow, metered flow and bypass flow circuits. The motive flow circuit is used to drive airframe ejectors and purge the fuel drain tank. The metered flow circuit provides fuel to the fuel nozzles. The bypass flow circuit retums excess fuel back to the fuel pump inlet. An airframe supplied fuel flow meter measures the amount of fuel flowing through the metered flow circuit.

The flow divider splits metered fuel flow into the primary and the secondary circuits with the engine running. During shut down the dump valve purges remaining fuel, trapped within the manifolds, to the fuel drain tank.

The primary and secondary fuel manifolds carries fuel to the 14 fuel nozzles and in the event of a defective packing, drains fuel leakage. The fuel nozzles delivers fuel to the combustion chamber. The fuel drain tank contains fuel from the previous engine shut down and will be purged, during the next engine run, into the low pressure fuel system at the fuel heater unit .

Types of fuel and additives Ref.: SB20004

Use of AVGAS limited to 150 hours/TBO

Fuel Filter/Heater Unit

Fig. 2 Fuel Filter/Heater Unit

Purpose: Pre-heat the fuel to prevent ice crystal formation

Construction: Consists of a low pressure fuel filter, an impending bypass indicator, a bypass valve (ref. fuel system), a heat exchanger,

a thermal sensor and an oil flow control valve

Operation: The heater housing has two circuits: lubricating oil and fuel.

Heat transfers from oil to fuel. A thermal sensor in the fuel circuit operates an oil flow control valve to maintain the required fuel temperature.

Fuel out temp. below 10°C = full oil flow, max. heating Fuel out temp. above 10°C = reduction of heat transfer Fuel out temp. above 32°C = full bypass, no heating Filter: 70 microns

Cleanable Buble Point test Impending bypass switch: Activates at 1.5 psid

Field replaceable Bypass valve: Opens at 3 psid

Fuel Pump

Fig. 3 Fuel Pump

Purpose: Provide high pressure fuel flow to the mechanical control unit to meet engine fuel requirements at any operating conditions

Description: Single stage gear type pump driven by the HP rotor through the accessory gearbox. The pump incorporates a 74 micron inlet strainer with integral bypass feature, a set of spur gears and a 10 micron outlet filter. The outlet filter is equiped with a bypass valve and an impending bypass switch. 100% NH = 3740 PPH (TYPICAL)

Operation: Rotation of the pump gears draw the low pressure fuel through the inlet strainer. Restricton in the system causes the fuel to pressurize and flow through the outlet filter out to the hydromechanical fuel control (HMU).

When blockage of the pump inlet strainer causes a pressure drop of 1.3 psid, the strainer lift off its seat and allow fuel to bypass the strainer.

When blockage of the pump outlet filter causes a pressure drop of 25 psid, the impending bypass switch sends a warning signal. When the pressure drop reaches 50 psid the bypass valve opens and send unfiltered fuel to the HMU.

Bypass fuel from the mechanical fuel control is returned to the inlet of the pump, through an ejector nozzle, to help maintain the inlet pressure to the pump gears.

Inlet strainer: cleanable (ELECTROSONIC)

Flow Divider Valve

Fig. 4 Flow Divider Valve

Purpose: Divides flow between primary and secondary fuel manifolds and dumps fuel from the manifolds on shutdown

Construction: Two concentric valves spring loaded to dump position Dump position: Purge fuel manifolds and nozzles from any remaining fuel

Prevents contamination of nozzles Fuel returns to engine

Primary flow position: 10 psi closes dump side of primary valve Opens flow to primary manifolds

10 nozzles begin to flow Primary and secondary flow position:

310 psi opens secondary valve Opens flow to secondary manifolds 14 additional nozzles begin to flow

Fuel Manifold Assy & Nozzles

Fig. 5 Fuel Manifold Assy & Nozzles

Purpose: Atomize and deliver fuel to the combustion chamber. Construction: Primary - secondary adapters

Primary flow through center orifice Secondary flow through annular orifice Locating pin on adapter

Secondary adapters Secondary flow only

Locating pin on gas generator case Positions # 1-4-8-12

Drain manifold Prevents fuel from leaking on the gas generator case Collects fuel manifold leakage and drains it overboard

Fuel Drain Ejector Tank

Fig. 6 Fuel Drain Ejector Tank

Purpose: Collect engine drain fuel and return it to the fuel heater upstream of the fuel pump. Construction: Tank

Float Valve Lever

Non- return valve Ejector pump

OPERATION

Fuel drained from the nozzles raises the tank fuel level and the float rises. During its movement, the float body lifts the lever which unseats the valve from the plug orifice.

The fuel pressure, acting on the upper end of the orifice, together with a small depression produced by the annulus at the orifice lower end, causes a pressure drop inside the plug orifice. The pressure drop unseats the non-return valve, permitting fuel to flow to the ejector pump. The fuel then is drawn by the ejector pump venturi action and returned to the engine low pressure fuel system.

73-20 CONTROLLING

Hydro - Mechanical Fuel Control Unit (Hmu)

Fig. 7 Hydro - Mechanical Fuel Control Unit (Hmu)

Features:

Provides metered flow for engine requirements Provides motiv flow for airframe ejector boost pomps Limits min / max fuel flow

Limits acceleration and deceleration rate Back up Nh speed control (manual mode)

Hmu Eec Mode

Fig. 8 Hmu EEC Mode

Motive flow valve: Opens to send fuel to airframe ejector boost pumps when supply pressure exceeds bypass pressure by 270 PSID.

High pressure relief valve: Opens at 1350 PSID to relieve excess pressure in HMU. Power lever valve: Manually controls metering orifice A1 for "manual mode",

and rotates potentiometer for "EEC mode".

Potentiometer: Connected to power lever valve, it reads position of lever and transmits (PLA) signal to EEC.

UP Towards min. WF stop (90 PPH). Closes windows A2 and A3.

DOWN Towards Max. WF stop (1350 PPH)Opens windows at A2 and A3. Pressure regulating valve: Maintains pressure differential of 23 PSID between

supply pressure and regulator pressure.

Torque motor: EEC controls torque motor. Increase current Torque motor valve opens. Decrease current Torque motor valve closes.

Enrichment solenoid: Enriches or de-enriches HMU manual schedule. EEC on - De-enriched - Solenoid up.- Energized EEC off - Enriched - Solenoid down.- De-energized

Min. pressurizing valve: Maintains a minimum pressure of 110 PSID in HMU before allowing fuel flow to the engine.

Cut-off valve: Shuts off flow to the engine, by forcing min pressurizing valve to close.

Note:

Hmu Manual Mode

Fig. 9 Hmu Manual Mode

Manual mode:

EEC off, torque motor de-energizes and closes. Enrichment solenoid de-energizes and moves down. Fixed fuel flow circuit then flows to Most Selector pushing it to the left and continuing to the pressure regulating valve. Differential pressure is now controlled via window A1 in the power lever valve.

Enrichment solenoid:

Up when EEC is on, blocking fixed fuel flow circuit to PRV, and allowing regulator pressure to control PRV via torque motor. Should the enrichment solenoid stay up (de-enriched) during a reversion to manual mode at take-off power, the engine would decelerate to min. flow. To prevent this, the solenoid is enriched (down) during take-off allowing the Most Selector to regulate the flow to the pressure regulating valve between the higher of two pressures.

As the aircraft climbs to higher altitudes and the EEC lowers the fuel flow in an effort to maintain NH constant, it becomes possible for the Most Selector to switch from EEC regulator pressure to manual fixed fuel flow pressure. When this happens the EEC can no longer reduce the fuel to control NH since authority has been switched to the manual schedule. Therefore, the enrichment solenoid must be de-enriched (up) after take-off.

Fault Detection System

Fig. 10 Fault Detection System

The control software contains various fault detection routines which allow the EEC to identify and accommodate system faults. The built-in-test infomms the pilot of the fault by setting the fault indicator. EEC hardware faults are detected by self test routines executed upon control initiation and at regular intervals during nommal operation. Sensor and input signal processing faults are detected by comparison of the input data with normal operating range and rate of change limits. Discrete switch input faults are identified by comparison logical input and output combinations.

The engine is controlled by the EEC (automatic mode) or by the pilot (manual mode) and a reversion from automatic to manual occurs under anyone of the following conditions:

- EEC detects a fault within itself

- EEC detects a fault in one of several components providing input pilot selection The ENG MANUAL light illuminates whenever a reversion has taken place.

The EEC FAULT light illuminates when a fault has been detected within the EEC or within the HMU PLA system

There are two types of reversion to manual: latching and non-latching. Latching fault:

- Once corrected, does not automatically result in the EEC resuming functioning

- The EEC must be pilot reset by cycling the 28 volts reset breaker or the ENG MANUAL switch Non-latching fault:

- Once corrected, results in the EEC resetting itself (ENG MANUAL light OFF) • Example: Loss of Nh signal when CLA is in feather

• EEC resets itself at engine start-up when Nh is > 25% Minor fault:

- Fault affecting accuracy but not integrity of control system Major fault:

- Fault affection integrity of control system - Always revert to manual

Fail fixed:

- Ensures no power loss during reversion to manual when a minor is fault detected

- Available when PLA and CLA are in the take-off range Operation:

During takeoff, upon detection of a minor fault the EEC will freeze the torque motor current at the level it was an instant before detection of the fault. The EEC will then revert to manual but there will be no power loss if fault occurred in steady state.

EEC Features & TSC Features

Fig. 11 EEC Features & TSC Features

EEC FEATURES

Command the handling bleed valve.

Keeps NH constant during cruise through various ambient conditions. Controls accel and decel rate based on Nh.

NP fuel governing functions

Maintain minimum NP at low power.

Schedule NP as a funciton of PLA in reverse. Limits maximum NP in reverse.

EEC SAFETY FEATURES

NH overspeed protection at 103%. -> EEC switches off.

NP > 100% or NP accelerating faster than a predetermined rate, EEC will reduce fuel flow to control NP within 105%. -> Feature enabled when NP > 80%.

TSC FEATURES

Auto-Feather System

Fig. 12 Auto-Feather System

Purpose: Detect an engine failure and signal airframe to feather

the failed engine propeller. System is used during take off only Components: TSC reads torque from sensor and manages auto-feather logic\ Arming: Auto-feather switch ON

Both PLA's in TO range

Both torque > 50.4% (+- 5.1%) "Ammed" light ON

Trigger: One engine torque < 19.4% (+-5.1%) Other engine torque > 50.4% (+-5.1%)

0.5 second later "Armed" light OFF, propeller feathers,

auxiliary pump activates and local NP fuel goveming is cancelled Disarming: Auto-feather switch OFF or

One PLA < TO range or Both PLA's < TO range or

Both engine torque < 50.4% (+- 5.1%) or Auto-feather triggered

Test: Both engines Nnning CLA at MAXIMUM rpm PLA's at flight idle Auto-feather switch ON A/F test switch 1 and 2 ON "Armed" light ON

Release one A/F switch

0.5 second later "Arrned" light off, propeller feathers,

auxiliary pump activates and local NP fuel goveming is cancelled

Governing

PLA:

Position of PLA represents a certain NH speed. The EEC will vary fuel flow to maintain NH as required by a schedule of a rating chart.

Cancel NP(T) Governing:

-When feathering propeller NP(T) fuel governing feature must be cancelled to avoid an overtorque, since EEC would otherwise try and maintain a minimum NP.

NP(T) fuel governing is cancelled whenever prop is feathered by 1. Auto-feather

2. Condition lever selecting electrical feather 3. Manual selecting feather (OHP)

or

NH Overspeed Test: NH OVSP ENG LH LH FI TEST OFF 1 TEST PLA FI PLA FI ENG RH SSEC DISABLE MADC 2 TRIM TEST

Fig. 13 LH Engine Test Panel

Checks EEC's 103% overspeed protection without running engine at high NH. When NH overspeed test switch is on, it resets limit to 60% NH.

Engine Trim:

TEST

LOCK

AUX PUMP

ENG

RH

ENG

LH

RH

3

4

3

4

ENG-TRIM

TAB

LH

GO

ACTR

Fig. 14 RH Engine Test Panel

Purpose: 1. To establish power loss when EEC reverts to manual. 2. To eliminate throttle staggers.

Procedure:

Run engine with EEC's off. Trim switches in minimum position. Set power as recommended by MM Remove power lever stagger by moving both power levers to mid position of stagger.

73-30 INDICATING

FUEL FLOW AND TEMPERATURE

FUNCTIONAL DESCRIPTION

The system indicates the fuel flow rate (consumption) and also the fuel temperature of the LH (RH) engine.

The signals supplied by the fuel flow transmitter and the fuel temperature sensor are indicated on the EICAS display.

The fuel flow transmitter is located on the right side of the engine next to the ignition exciters. The fuel temperature sensor is located on the left side of the engine on the fuel heater valve (fuel outlet).

The fuel flow and temperature indication system consists of the following main components: - Fuel flow transmitter

- Fuel temperature sensor - EICAS on the central displays.

OPERATION

Fuel supplied to the engine flows through the fuel flow transmitter. The transmitter is driven by a turbine driver which generates torque and thus turns the measuring unit.

The fuel flow rate output-signal from the transmitter is proportional to the time displacement between two sinus pulse signals.

This generated signal is supplied for indication processing to the DAU 1 (DAU 2). Subsequently the EICAS display indicates the fuel flow rate (FF) in LBS / HR (or KG / H). The indicating range is between 0 and 1 200 LBS / HR.

The fuel temperature sensor supplies resistance signals which correspond to the temperature of the fuel which is present at the sensor. The signal supplied to the DAU 1

(DAU 2) is indicated on the EICAS display in 0C. The indicating range between - 600C and 990C (+/-20C).

EICAS Indication MFD PAGE Indication Fault or Condition FUEL PAGE digital - 600 to + 990 C white amber

Fuel temperature indicating LH / RH

FUEL PAGE digital / white

0 to 1200 LBS / HR

FF LH / RH

Fuel flow indicating LH / RH

ENGINE PAGE digital / white

0 to 1200 LBS / HR

FF LH / RH

Fuel flow indicating LH / RH

digital / white

0 to 1200 LBS / HR

FF LH / RH

Fuel Flow Primary EICAS Page Honeywell

MAIN

END 2870 500 FF LBS / HR FQ LBS 2870 500 80.3 NH 800 ITT 80.2 NP 97.0 TQ 80.3 800 80.2 0 2000 CAB ALT V / S FT FPM NU ND OIL TEMP OIL PRSS COPY 97.0 0 ° 0 °

FUEL FILTER / PRESSURE

FUNCTIONAL DESCRIPTION

The system monitors the fuel pressure and also the fuel heater inlet (low pressure) and fuel pump outlet (high pressure) filter for clogging. The signals supplied by the low fuel pressure switch or by the HP- or LP - fuel warning switches are indicated on the EICAS display.

The low fuel pressure switch is located on the left side on the fuel heater. The fuel warning switches are also located on the left side. The HP-fuel warning switch is installed on the fuel pump outlet filter and the LP fuel warning switch on the fuel heater inlet filter.

The pressure indication system consists of the following components: - Low fuel pressure switch

- HP-fuel warning switch - LP-fuel warning switch - EICAS on the central display

OPERATION

If the fuel heater inlet filter or fuel pump outlet filter is clogged, the HP-fuel warning switch or LP-fuel warning switch installed in the bypass circuit connects ground to the DAU 1 (DAU 2). The EICAS subsequently displays caution messages.

If the fuel pressure below the minimum value (< 40 +/- 3kPa) the low-fuel pressure switch connects ground to the DAU 1 (DAU 2) and the EICAS displays caution messages.

CAS FIELD Indication MFD PAGE Indication Fault or Condition AMBER

L / R FUEL PRSS LOW

Low fuel pressure condition LH /RH ENGINE Page

AMBER

PRSS LOW (LH) (RH)

Low fuel pressure condition LH /RH

FUEL Page AMBER

PRSS LOW (LH) (RH)

Low fuel pressure condition LH /RH

AMBER

FUEL FILT

BYPASS

Fuel filter (HP) clogged

FUEL Page AMBER

HP FILTER (RH) (RH)

HP - fuel filter LH RH clogged

SYS MAINT AMBER

L R LP FILTER

Fuel -Flow / -Used / -Temperature / -Pressure and HP Filter on Fuel Page Honeywell

FLIGHT

CONTROL

HYDR

ENGINE

FUEL

NEXT

SYSTEM 1/3

Fuel Flow on Engine Page Honeywell

FLIGHT

CONTROL

HYDR

ENGINE

FUEL

NEXT

SYSTEM 1/3

LP Fuel Filter on System Maintenance Page Honeywell

SYSTEM 3/3

CPCS/

OXYGEN

DOORS

SYS

MAINT

SENSOR

DATA

NEXT

FUEL

L TRANSFER MON 021292

R TRANSFER MON 021292

CPCS

BACKUP INSTRUMENTS

OXYGEN

QTY ACCURACY

ICE PROTECT

L

R

L

R

SWDW TEMP

SWDW TEMP

FWDW TEMP

FWDW TEMP

HYDRAULICS

FLIGHT CONTROLS

ELECTR

APU

OVERTEMP EGT

OVERCURRENT ECU

OIL TEMP HIGH

ENGINE

L RGB CHIPS DETECT

R RGB CHIPS DETECT

L ENG CHIPS DETECT

R ENG CHIPS DETECT

PROXI MAINT

L LP FILTER

R LP FILTER

L MAIN OIL FILT

R MAIN OIL FILT

L SCAV OIL FILT

R SCAV OIL FILT

Fuel Flow on RMU Page 2

CPCS AUTO FAIL

PITOT S HEAT FAIL

L AOA FAIL

R AOA FAIL

BATT 1 FAIL

BATT 2 FAIL

RUDDER LIMITED

600

FF

600

85

OIL TEMP

84

61

OIL PRS

61

INDEX

Auto-Feather System 16 CONTROLLING 9 DISTRIBUTION 2

EEC Features & TSC Features 15 EEC SAFETY FEATURES 15 Fault Detection System 13 Fuel Drain Ejector Tank 8 Fuel Filter / Pressure 22 Fuel Filter/Heater Unit 4

Fuel -Flow / -Used / -Temperature / -Pressure and HP Filter on Fuel Page 23

Fuel Flow and Temperature 19

Fuel Flow on Engine Page 24 Fuel Flow on RMU Page 2 26 Fuel Flow Primary EICAS Page 21 Fuel Manifold Assy & Nozzles 7 Fuel System 2

Hmu Eec Mode 10 Hmu Manual Mode 12

Hydro - Mechanical Fuel Control Unit (Hmu) 9 INDICATING 19

LP Fuel Filter on System Maintenance Page 25 TSC FEATURES 15

LIST OF ILLUSTRATIONS

Fig. 1 Fuel System ...2

Fig. 2 Fuel Filter/Heater Unit ...4

Fig. 3 Fuel Pump ...5

Fig. 4 Flow Divider Valve...6

Fig. 5 Fuel Manifold Assy & Nozzles...7

Fig. 6 Fuel Drain Ejector Tank...8

Fig. 7 Hydro - Mechanical Fuel Control Unit (Hmu)...9

Fig. 8 Hmu EEC Mode...10

Fig. 9 Hmu Manual Mode ...12

Fig. 10 Fault Detection System ...13

Fig. 11 EEC Features & TSC Features...15

Fig. 12 Auto-Feather System...16

Fig. 13 LH Engine Test Panel ...18

Fig. 14 RH Engine Test Panel ...18

Fig. 15 Fuel Flow Primary EICAS Page ...21

Fig. 16 Fuel -Flow / -Used / -Temperature / -Pressure and HP Filter on Fuel Page ...23

Fig. 17 Fuel Flow on Engine Page ...24

Fig. 18 LP Fuel Filter on System Maintenance Page ...25

End of ATA Chapter 73

Engine Fuel and Control