FADEC System | Full Authority Digital Engine Control Overview

FADEC System

Full Authority Digital Engine Control (FADEC) System Description & Operation

FADEC Fuel Control Systems

A full authority digital electronic control (FADEC) is a most advance system to control fuel flow on modern turbine engine models. For the majority of current turbine engine models, a full authority digital electronic control (FADEC) system has been incorporated to regulate fuel flow. A hydromechanical fuel control backup system is absent from a real FADEC system. The system makes use of electronic sensors to supply the EEC with data about engine parameters. The EEC collects the data required to calculate the fuel flow rate and sends it to a fuel metering valve. The gasoline metering valve only responds to the EEC's directives. The fuel delivery system's computational component, the EEC, is a computer, and the metering valve measures the fuel flow. Many different types of turbine engines, ranging from APUs to the largest propulsion engines, utilise FADEC systems.

FADEC Function

True full authority digital engine controls don't offer any kind of manual override, giving the computer entire control over the engine's operational parameters. The engine fails in the event of a complete FADEC failure. If the engine is digitally and electronically controlled yet has a human override feature, it is only referred to as an EEC or ECU. Despite being a part of a FADEC, an EEC is not a FADEC in and of itself. Until the pilot requests to take over, the EEC makes all decisions when operating alone.

The air density, throttle position, engine temperatures, engine pressures, and a variety of other factors are all input variables that FADEC uses to operate. The EEC receives the inputs and processes them up to 70 times per second. These data are used to compute and then apply engine operating parameters including fuel flow, stator vane position, air bleed valve position, and others. Engine starting and restarting are likewise under FADEC's supervision. The FADEC's primary goal is to deliver the best engine performance under a certain set of flight conditions.

The manufacturer may programme engine restrictions, get engine health and maintenance reports, and ensure that engines are operated efficiently thanks to FADEC. For instance, the FADEC can be set up to automatically conduct the necessary actions without the pilot's input to prevent exceeding a specific engine temperature.

FADEC Fuel Control Turbine Engine

Large high-bypass turbofan engines frequently employ fuel control systems of the FADEC type. The main element of the FADEC engine fuel control system is the EEC. The EEC is a computer that manages how the engine runs. The internal physical separation of the two computers within the EEC housing's two electronic channels allows for natural convection cooling. Typically, the EEC is situated in a section of the engine nacelle that stays cool while the engine is running. Shock mounts are used to secure it to the lower-left fan casing.

To control engine operation, the EEC computer uses input from numerous engine sensors and aircraft systems. To control engine power or thrust, it receives electrical signals from the flight deck. The throttle lever angle resolver sends a signal to the EEC proportional to the location of the thrust lever. Most engine parts are under the supervision of the EEC, which also gets input from them. For engine operation, the EEC receives data from numerous components.

The aircraft electrical system or the permanent magnet alternator provide power for the EEC (PMA). The PMA directly feeds power to the EEC when the engine is operating. Every aspect of engine function is managed by the two-channel EEC computer. Each channel, which is a separate computer, has full control over how the engine runs. The processor performs all control calculations and provides all the information needed to create the control signals for the solenoids and torque motors. In order to determine which EEC channel will best control the output driver for a torque motor or solenoid bank, the cross-talk logic examines data from channels A and B. Each output driver is under the control of the principal channel. If the cross-talk logic determines that the other channel is superior for controlling a particular bank, the EEC switches that bank's control to the alternative channel. The EEC has output driver banks that provide the engine parts with the control signals. Control signals are provided to the driver banks through each EEC channel. For storing performance and maintenance data, the EEC features both volatile and nonvolatile memory.

By using a mode selection switch, the EEC can manage the engine thrust in two different ways. Engine thrust is controlled by EPR in the standard mode and by N1 in the alternative mode. The EEC resets when the fuel control switch is switched from run to cutoff. All fault information is saved in the nonvolatile memory during this reset. To supply fuel flow for combustion, the fuel metering unit's metering valve is controlled by the EEC. The gasoline metering device is fixed to the front of the fuel pump and located on the front face of the gearbox. In order to start or stop the flow of fuel, the fuel metering unit's minimum pressure and shutdown valve receives a signal from the EEC.

Thermocouples, rotary differential transformers, and linear variable differential transformers are used by the EEC to obtain position feedback for various engine parts. These sensors transmit data on engine parameters to the EEC from various systems. The high-pressure fuel shutoff valve that regulates fuel flow is controlled by the fuel control run cutoff switch. The fuel outlet line on the back of the fuel/oil cooler is where the fuel temperature sensor thermocouple attaches. It communicates this information to the EEC.

The gasoline metering unit's metering valve is moved by the EEC using a torque motor driver. The other FMU operations are managed by the EEC via solenoid drivers. Through torque motors and solenoids, the EEC also regulates a number of additional engine subsystems, including the fuel and air oil coolers, bleed valves, variable stator vanes, turbine cooling air valves, the turbine case cooling and other system.

Three on each side and one on the bottom make up the seven electrical connections that each EEC channel has. The inputs of the two connections on top of the EEC are shared by both channels. These are the test connector and the programming plug. The programming plug chooses the appropriate EEC software based on the engine's thrust rating. A lanyard is used to fasten the plug to the engine fan case. The plug stays with the engine when the EEC is taken out. On the bottom of the EEC, there are three pneumatic connectors for each channel. A signal proportional to the pressure is provided to the associated and opposing EEC channels via transducers inside the EEC. The ambient pressure, burner pressure, LPC exit pressure, and fan inlet pressure are the pressures that the EEC measures. The cable colour that links the EEC to each channel's sensors is unique. While channel B sensor signals are green, channel A wiring is blue. The thermocouple indications are yellow, while the non-EEC circuit wire is grey.

Fuel System Operation

The fuel system of the aeroplane supplies fuel to the fuel pump. The fuel is pressurized and sent to the fuel/oil cooler via the pump's low-pressure boost stage (FOC). Fuel travels from the FOC to the high-pressure main stage of the pump after passing through the fuel pump filter element. Fuel pressure is raised by the high-pressure main stage and sent to the fuel metering unit (FMU). Additionally, it provides servo fuel to the engine parts, including the servo fuel heater. The distribution valve receives fuel for combustion (metered fuel) through the fuel flow transmitter.

The fuel supply manifolds receive metered fuel from the fuel distribution valve. The fuel supply manifolds feed the metered fuel to the fuel injectors, which then dispense it into the engine for burning. A disposable fuel filter element is located within the fuel pump housing. The EEC receives a signal from the fuel filter differential pressure switch informing it that the filter is virtually blocked. If the filter element clogs, unfiltered fuel can then get through.

Safety Concern

Safety is a major problem because the engines' operation depends so significantly on automation. Two or more independent but identical digital channels serve as redundancy. Any engine function may be provided by any channel without limitations. In order to provide fault-tolerant engine management, FADEC also keeps an eye on a range of data from the aircraft's linked systems and the engine subsystems.

A 2015 Airbus A400M catastrophe in Seville, Spain, has been linked to engine management issues that caused up to three engines to lose thrust at the same time. On May 29, Airbus Chief Strategy Officer Marwan Lahoud declared that the deadly crash was the result of improperly installed engine control software. There are no structural flaws in the aeroplane, however the final assembly is seriously lacking in quality.

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