Pilote automatique (Autopilot)

Qu'est-ce que le pilote automatique ?

An autopilot (A/P) is an automatic flight control system that manages an aircraft's attitude, heading, altitude, and speed without requiring the pilot to continuously manipulate the flight controls. Rather than replacing pilots, autopilot frees them to monitor systems, communicate with ATC, and plan ahead — particularly on long-haul flights where manual flying for hours would cause fatigue.

Fonctionnement

Modern autopilot systems receive inputs from multiple sensors — inertial reference units, air data computers, GPS receivers, and radio navigation aids — then issue commands to the aircraft's control surfaces via servo actuators. The system continuously compares actual flight path against the desired flight path and corrects deviations. Pilots interact with autopilot through a Mode Control Panel (MCP) or Flight Control Unit (FCU), dialing in target altitude, heading, vertical speed, and airspeed.

• Heading mode: Maintains a selected magnetic heading
• Altitude hold: Locks the aircraft at a specified pressure altitude
• VNAV/LNAV: Follows vertical and lateral profiles computed by the Flight Management System
• Autoland: Coupled with ILS, can execute a fully automatic landing in Category III low-visibility conditions

On Airbus aircraft, autopilot works in conjunction with the fly-by-wire flight envelope protection — the autopilot cannot command maneuvers that exceed structural or aerodynamic limits.

Évolution et systèmes modernes

The first practical autopilot was demonstrated by Lawrence Sperry in 1914 using a gyroscope-stabilized system. By the 1950s, analog autopilots were standard on airliners. Today's digital flight control computers — such as the Boeing 777's AFCS (Automatic Flight Control System) or the Airbus A320's Flight Augmentation Computer — can manage an entire flight from shortly after takeoff to touchdown. The Boeing 747 introduced autoland in revenue service, and modern widebodies like the A350 and 787 feature triple-redundant autopilot channels for fail-operational capability.

Exigences réglementaires

FAA FAR Part 121 and EASA CS-25 mandate autopilot for extended overwater operations (ETOPS) and certain high-altitude routes. Category IIIb autoland operations require autopilot systems with demonstrated reliability of at least 10⁻⁷ failure probability per flight hour. Pilots must be type-rated on each autopilot variant and conduct periodic manual flying to maintain hand-flying proficiency.