Fly-by-Wire

Was ist Fly-by-Wire?

Fly-by-wire (FBW) is a flight control architecture in which the physical connection between the pilot's sidestick or yoke and the aircraft's control surfaces — ailerons, elevators, and rudder — is replaced by electronic signals processed through flight control computers. The pilot's inputs become digital commands that computers interpret and translate into surface deflections, often with built-in envelope protection that prevents the aircraft from exceeding its structural or aerodynamic limits.

Funktionsweise

When a pilot moves the sidestick on an Airbus A320, sensors measure the deflection and send electrical signals to the Flight Control Primary Computers (FCPCs). These computers calculate the appropriate control surface positions based on the pilot's intent, current flight conditions (speed, angle of attack, load factor), and programmed flight envelope limits. Servo actuators then physically move the surfaces. The system operates with triple or quadruple redundancy — if one computer fails, others take over seamlessly.

• Normal law: Full envelope protection active (bank angle limit, pitch protection, overspeed protection)
• Alternate law: Partial protection, activated when sensors degrade
• Direct law: Pilot inputs command surfaces directly, no protection — last resort

FBW integrates tightly with autopilot and the glass cockpit, sharing sensor data and computer infrastructure.

Entwicklung und moderne Systeme

The Concorde used an early analog FBW system in the 1970s. The Airbus A320, entering service in 1988, was the first commercial airliner with a fully digital FBW system and sidestick controllers. Boeing adopted FBW on the 777 (1995) and later the 787, but retained the conventional yoke rather than Airbus's sidestick. The Airbus A380 and A350 use FBW with force-feedback sidesticks. Military aircraft like the F-16 were pioneering FBW in the 1970s, as their inherently unstable aerodynamic designs are only flyable via computer-mediated controls.

Regulatorische Anforderungen

FBW systems must satisfy FAA AC 25.1309 and EASA AMC 25.1309 design assurance requirements, demonstrating catastrophic failure probability below 10⁻⁹ per flight hour. Software is developed to DO-178C Level A (highest integrity). Hardware follows DO-254. Certification requires extensive iron-bird rig testing, simulator validation, and flight test demonstration of all degraded modes before revenue operations begin.