ATR 72-600 Fuel System

Fuel System Overview

Introduction to the Fuel System

• The discussion begins with an overview of the fuel system, outlining the structure and components that will be covered: system description, fuel tanks, vent system, refuel/defuel systems, engine feed system, and controls/indicators.

Components of the Fuel System

• The ATR's fuel system includes two integral wing tanks capable of holding 2,500 kg each. Each tank features a feeder tank near the wing root that holds 160 kg of fuel and contains both an electrically driven pump and a jet pump.

• The maximum allowable fuel imbalance between tanks is 730 kg. Two fuel lines run through the wing center box for cross-feeding engines and refueling operations.

Vent System Functionality

Venting Mechanisms

• A vent line prevents vapor concentration in the tanks while providing positive pressure during aircraft maneuvers. Each wing tank has a surge tank vented through individual ducts.

• A flush neck event inlet allows atmospheric pressure into the surge tank while preventing ice accumulation; these inlets are designed to withstand lightning strikes.

Surge Tank Operations

• A float valve collects fuel in the surge tank which is then returned to the main wing tank via associated ducts. This mechanism also helps prevent overfilling during refueling by discharging excess fuel overboard if necessary.

Refueling Procedures

Refueling Systems

• The aircraft uses a single-point pressurized refueling system with gravity refueling options available via caps on top of each wing tank.

• Refueling can be completed in approximately 16 minutes by connecting a line to a rear-mounted connector on the right main landing gear fairing.

Safety Precautions During Refueling

• Important safety measures include avoiding switch operations (especially ground power unit activation), smoking, cell phone usage, and ensuring no thunderstorms are nearby during refueling activities.

Defueling Process

Defueling Mechanism

• Defueling utilizes the same single-point fueling system by applying pressure to open valves downstream from the connector.

Engine Feed System Details

Engine Fuel Supply

• Each engine receives fuel from its respective feeder tank located within each wing; these tanks remain full to mitigate negative or lateral load factors.

• Feeder tanks hold 200 L of fuel and incorporate both electrical pumps and jet pumps for consistent supply throughout flight conditions.

Pump Operations

• Electrical pumps powered by DC essential bus provide continuous flow; they operate primarily at startup before switching to jet pump supply once engines are running.

Fuel Flow Management

Fuel Pathway Description

• After passing through various valves including low-pressure (LP), high-pressure (HP), filters, and hydromechanical units (HMU), fuel flows into engines where some is returned for motive flow purposes back into feeder compartments.

Fuel System Overview and Operations

Motive Flow Valve and Engine Jet Pump Functionality

• The motive flow valve opens to allow fuel through to the engine jet pump, controlled by a push button on the fuel panel. If deselected, the valve remains closed.

• A portion of fuel is returned from the engine jet pump to the feeder jet pump via a check valve, which then transfers fuel from the main tank to the feeder tank for further pumping.

Electrical Pump Activation Conditions

• An electrical pump activates automatically if an engine jet pump's output drops below 5 PSI, provided its associated push button is selected. Below 4 PSI triggers an amber low-pressure light.

• Automatic activation of electrical pumps can also occur during cross-feed operations or if the feeder tank's fuel quantity falls below 160 kg, indicated by an amber low-level message.

Cross Feed System and Operations

• The cross feed system allows either tank to supply fuel to the opposite engine through a cross-feed valve controlled by a push button on the fuel panel. This system helps correct fuel imbalances between tanks.

• To balance tanks when one is lower than another, press the cross-feed button; this turns on both electrical pumps while shutting off the pump in the lower tank until levels equalize.

Single Engine Operation and Fuel Quantity Indication

• In single-engine operation scenarios, both tanks supply fuel without shutting down any electrical pumps to maintain balance. This ensures continuous supply from both sources.

• The fuel quantity indication system calculates and displays each tank's weight-based fuel quantity using capacitance probes located in each wing tank, with independent channels for redundancy in case of failure.

Magnetic Level Indicators and Control Panel Layout

• On-ground readings can be taken using magnetic level indicators accessed at each wing tank's bottom; these readings help derive quantities based on conversion tables marked in centimeters of fuel volume.

• The control panel features buttons for electrical pumps and cross-feed valves arranged schematically for clarity; pressing a pump button activates its corresponding electrical pump under specific conditions like low delivery pressure from an engine jet pump.

Fuel System Operations and Indicators

Engine Jet Pump Functionality

• The MFD indicates that when the pump push button is pressed, the engine jet pump's motive flow valve opens, but it remains closed if fuel pressure is insufficient.

• The operation of the engine jet pump is controlled by a pressure switch; it automatically shuts off after 30 seconds once pressure exceeds 8.5 PSI.

• After engine start, the Green Run light on the MFD goes out, and "run" is replaced with a vertical green flow line in the associated pump icon when the electrical fuel pump is deactivated.

Low Pressure Valve Indicators

• The LP valve position indicator above each pump push button shows whether the low-pressure valve is open or closed; it’s controlled solely by the associated engine fire handle.

• When open, a green inline flip bar appears; when closed, a green crossline flip bar displays. The flip bar disappears during transit.

Fuel Supply Pressure Monitoring

• An amber low-pressure light activates when fuel supply pressure drops below 4 PSI, indicating potential issues like loss of electrical fuel pumps or blockage in supply lines.

• If this occurs, a single chime sounds, master caution lights flash, and an amber feed low-pressure message appears on both EWD and MFD.

Cross Feed Valve Operation

• Pressing the cross feed push button opens the cross feed valve and activates both electrical pumps, illuminating their Green Run lights and displaying a "fuel cross feed" message on the memo panel.

• Selecting out on the push button closes the cross feed valve; its status changes to show a vertical green flare bar only visible when opened or closed.

Fuel Quantity Management

• Fuel quantity displayed on MFD turns amber when levels drop below 160 kg; this triggers automatic activation of associated electrical fuel pumps.

• A low fuel condition causes master caution lights to flash alongside an amber warning message on EWD for further alerts to crew members.

Critical Alerts for Low Fuel Conditions

• If fuel quantity falls below 50 kg in any tank, it will be shown in red reverse video for immediate attention from operators regarding critical levels.

• The LP valve and cross feed valve are visually represented as circles on MFD; their positions indicate operational status within system diagrams.

Electrical Pump Status Indications

• Each electrical pump's status is depicted as squares on-screen with solid green lines showing pressurized states while outlines indicate non-pressurized conditions.

• Clog indications appear if there’s excessive loss across any part of the fuel system.