Full Authority Digital Engine Control (FADEC)

What Is FADEC?

Full Authority Digital Engine Control (FADEC) is an electronic system that governs all aspects of an aircraft engine's operation. Unlike older hydromechanical fuel controls where the pilot directly commanded fuel flow, FADEC interprets crew thrust lever inputs and translates them into precise fuel scheduling, variable vane positioning, and bleed air management — optimizing performance at every point in the flight envelope while preventing over-temperature, over-speed, and surge conditions.

How It Works

FADEC consists of two or more redundant Electronic Engine Controllers (EECs) running identical software. Key operational characteristics:

• Full authority: No mechanical backup. FADEC commands directly control all engine actuators — fuel metering valves, variable stator vanes, bleed valves, and ignition.
• Sensor fusion: Processes dozens of inputs including N1/N2 shaft speeds, Exhaust Gas Temperature (EGT), ambient pressure (P0), total air temperature (TAT), and throttle lever angle (TLA).
• Dual-channel redundancy: Two independent channels continuously cross-check each other. If one fails, the other takes over with no interruption.
• Self-powered: FADEC generates its own electrical power via a Permanent Magnet Alternator (PMA) on the engine, ensuring operation even during electrical emergencies.
• Envelope protection: Automatically limits fuel flow to prevent EGT exceedances, fan surge, stall, and overspeed — pilots cannot command beyond safe limits.

Performance Specifications

• Response time: Adjusts fuel flow in milliseconds to compensate for atmospheric disturbances and power demand changes
• Fuel savings: Optimized combustion scheduling can save 1–3% fuel compared to hydromechanical controls
• EGT margin protection: Continuously targets optimal turbine inlet temperature, maximizing engine life between shop visits
• Fault codes: FADEC stores up to hundreds of fault codes accessible during maintenance via ACARS datalink or ground stations
• Update cycle: Control laws run at 20–80 Hz processing loops depending on system design

Aircraft Examples

• Airbus A320 Family: FADEC on CFM56 and LEAP engines — integrated with fly-by-wire flight management for autothrust
• Boeing 777: FADEC on GE90, PW4090, and Trent 800 engines — pioneered use of thrust management computer integration
• Airbus A380: FADEC on all four GP7200 / Trent 970 engines with cross-engine monitoring
• Bombardier CRJ series: FADEC on General Electric CF34 — enables single-lever thrust management

FADEC is conceptually related to Fly-by-Wire systems that govern flight control surfaces. Both replace mechanical linkages with digital computers for precision and safety. The system also manages Bleed Air extraction from the engine compressor.