FADEC (Full Authority Digital Engine Control)

Definition

FADEC is a system consisting of a 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.

Description

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.

Advantages

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)

Saves weight

Disadvantages

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. Upon total FADEC failure, pilots have no manual controls for engine restart, throttle, or other functions. Single point of failure risk can be mitigated with redundant FADECs (assuming that the failure is a random hardware failure and not the result of a design or manufacturing error, which may cause identical failures in all identical redundant components).

High system complexity compared to hydromechanical, analogue or manual control systems

High system development and validation effort due to the complexity

Whereas in crisis (for example, imminent terrain contact), a non-Fadec engine can produce significantly more than its rated thrust, a FADEC engine will always operate within its limits.