Full authority digital engine (or electronics) control (FADEC) is a system consisting of digital computer, called an electronic engine controller (EEC) or engine control unit (ECU), and its related accessories that control all aspects of aircraft engine performance. FADECs have been produced for both piston engines and jet engines.
The goal of any engine control system is to allow the engine to perform at maximum efficiency for a given condition. The complexity of this task is proportional to the complexity of the engine. Originally, engine control systems consisted of simple mechanical linkages controlled by the pilot, but then evolved and became the responsibility of the third pilot-certified crew member, the flight engineer. By moving throttle levers directly connected to the engine, the pilot or the flight engineer could control fuel flow, power output, and many other engine parameters.
Following mechanical means of engine control came the introduction of analog electronic engine control. Analog electronic control varies an electrical signal to communicate the desired engine settings. The system was an evident improvement over mechanical control but had its drawbacks, including common electronic noise interference and reliability issues. Full authority analogue control was used in the 1960s and introduced as a component of the Rolls Royce Olympus 593 engine of the supersonic transport aircraft Concorde. However, the more critical inlet control was digital on the production aircraft.
Following analog electronic control, the logical progression was to digital electronic control systems. Later in the 1970s, NASA and Pratt and Whitney experimented with the first experimental FADEC, first flown on an F-111 fitted with a highly modified Pratt & Whitney TF30 left engine. The experiments led to Pratt & Whitney F100 and Pratt & Whitney PW2000 being the first military and civil engines, respectively, fitted with FADEC, and later the Pratt & Whitney PW4000 as the first commercial "dual FADEC" engine. The first FADEC in service was developed for the Harrier II Pegasus engine by Dowty & Smiths Industries Controls.
True full authority digital engine controls have no form of manual override available, placing full authority over the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails. If the engine is controlled digitally and electronically but allows for manual override, it is considered solely an EEC or ECU. An EEC, though a component of a FADEC, is not by itself FADEC. When standing alone, the EEC makes all of the decisions until the pilot wishes to intervene.
FADEC works by receiving multiple input variables of the current flight condition including air density, throttle lever position, engine temperatures, engine pressures, and many other parameters. The inputs are received by the EEC and analyzed up to 70 times per second. Engine operating parameters such as fuel flow, stator vane position, bleed valve position, and others are computed from this data and applied as appropriate. FADEC also controls engine starting and restarting. The FADEC's basic purpose is to provide optimum engine efficiency for a given flight condition.
FADEC not only provides for efficient engine operation, it also allows the manufacturer to program engine limitations and receive engine health and maintenance reports. For example, to avoid exceeding a certain engine temperature, the FADEC can be programmed to automatically take the necessary measures without pilot intervention.
With the operation of the engines so heavily relying on automation, safety is a great concern. Redundancy is provided in the form of two or more, separate identical digital channels. Each channel may provide all engine functions without restriction. FADEC also monitors a variety of analog, digital and discrete data coming from the engine subsystems and related aircraft systems, providing for fault tolerant engine control.
A typical civilian transport aircraft flight may illustrate the function of a FADEC. The flight crew first enters flight data such as wind conditions, runway length, or cruise altitude, into the flight management system (FMS). The FMS uses this data to calculate power settings for different phases of the flight. At takeoff, the flight crew advances the throttle to a predetermined setting, or opts for an auto-throttle takeoff if available. The FADECs now apply the calculated takeoff thrust setting by sending an electronic signal to the engines; there is no direct linkage to open fuel flow. This procedure can be repeated for any other phase of flight.
In flight, small changes in operation are constantly made to maintain efficiency. Maximum thrust is available for emergency situations if the throttle is advanced to full, but limitations can’t be exceeded; the flight crew has no means of manually overriding the FADEC.
- Better fuel efficiency
- Automatic engine protection against out-of-tolerance operations
- Safer as the multiple channel FADEC computer provides redundancy in case of failure
- Care-free engine handling, with guaranteed thrust settings
- Ability to use single engine type for wide thrust requirements by just reprogramming the FADECs
- Provides semi-automatic engine starting
- Better systems integration with engine and aircraft systems
- Can provide engine long-term health monitoring and diagnostics
- Number of external and internal parameters used in the control processes increases by one order of magnitude
- Reduces the number of parameters to be monitored by flight crews
- Due to the high number of parameters monitored, the FADEC makes possible "Fault Tolerant Systems" (where a system can operate within required reliability and safety limitation with certain fault configurations)
- Can support automatic aircraft and engine emergency responses (e.g. in case of aircraft stall, engines increase thrust automatically).
- Saves weight
- Full authority digital engine controls have no form of manual override available, placing full authority over the operating parameters of the engine in the hands of the computer. If a total FADEC failure occurs, the engine fails. In the event of a total FADEC failure, pilots have no way of manually controlling the engines for a restart, or to otherwise control the engine. As with any single point of failure, the risk can be mitigated with redundant FADECs.
- High system complexity compared to hydromechanical, analogue or manual control systems
- High system development and validation effort due to the complexity
- Engineering processes must be used to design, manufacture, install and maintain the sensors which measure and report flight and engine parameters to the control system itself.
- Software engineering processes must be used in the design, implementation and testing of the software used in these safety-critical control systems. This requirement led to the development and use of specialized software such as SCADA.
NASA has analyzed a distributed FADEC architecture rather than the current centralized, specifically for helicopters. Greater flexibility and lower life cycle costs are likely advantages of distribution.
See also 
- "Chapter 6: Aircraft Systems" (PDF). Pilot's Handbook of Aeronautical Knowledge. Federal Aviation Administration. 2008. pp. page 6–19. Retrieved 2009-02-09.
- Gunston (1990) Avionics: The story and technology of aviation electronics Patrick Stephens Ltd, Wellingborough UK. 254pp, ISBN 1-85260-133-7
- "Safran Electronics Canada: FADEC and EEC". Retrieved 2010-04-30.
- "Hispano-Suiza: Digital Engine Control". Retrieved 2007-03-09.
- Moren, Chuck. Interview with student. FADEC. Embry-Riddle Aeronautical University, Daytona Beach. 2007-03-13.
- www.faa.gov [[Federal Aviation Regulations|Title 14 CFR: Federal Aviation Regulations]]. FAA. 2007-03-10. Wikilink embedded in URL title (help)
- Harrier flies with digitally controlled Pegasus - a 1982 article in Flight International magazine
- Active-control engines a 1988 Flight International article on FADEC engines