Following the Airbus A320 emergency airworthiness action, everyone will be talking about the ELAC (Elevator Aileron Computer) manufactured by Thales, which caused a sudden pitch-down without pilot input on JetBlue 1230 back in October.

So here’s everything you need to know about ELAC.

The ELAC System in the Airbus A320: The Brains Behind Pitch and Roll Control

At the heart of the sophisticated fly-by-wire flight control system of the Airbus A320 lies the ELAC (Elevator Aileron Computer). This crucial component acts as one of the primary computational units that translate pilot commands into precise movements of the aircraft’s fundamental control surfaces: the elevators and the ailerons. ELAC plays a pivotal role in ensuring the aircraft’s stability and enabling smooth, safe, and efficient flight.

What is ELAC?

ELAC stands for Elevator Aileron Computer. On the A320, there are two main ELAC computers—ELAC 1 and ELAC 2—which operate together as essential elements of the aircraft’s fly-by-wire architecture. This system relies on electrical signals, rather than traditional mechanical cables, to transmit control inputs from the cockpit to the flight control surfaces.

Key Functions of the ELAC System:

Elevator Control:

The elevators are control surfaces located on the horizontal tailplane of the aircraft. They govern movement around the lateral axis (pitch), determining whether the aircraft ascends or descends. ELAC receives signals from the pilot’s sidestick and translates them into precise commands to move the elevators, achieving the desired pitch attitude.

Aileron Control:

Ailerons are control surfaces situated on the trailing edge of the wings. They manage movement around the longitudinal axis (roll), controlling the aircraft’s banking to the left or right. The ELAC processes pilot inputs and moves the ailerons to achieve the intended bank angle.

Implementing Flight Control Laws:

One of ELAC’s most critical responsibilities is enforcing the pre-programmed flight control laws embedded within the Airbus computers. These laws ensure the aircraft responds to pilot commands in a calculated and safe manner, providing protection against maneuvers that could exceed operational limits (such as overspeed or critical angles of attack).

Fault Monitoring and Redundancy:

The ELAC system includes a high degree of redundancy to ensure safety. If one ELAC computer malfunctions, the other can seamlessly take over. ELAC also continuously monitors the performance of control surfaces and associated systems, issuing warnings to the crew if any anomalies are detected.

ELAC 1 and ELAC 2: Distribution and Responsibility

ELAC 1: Primarily controls the ailerons and certain elevator functions, especially those relying on the blue hydraulic system.

ELAC 2: Primarily controls the elevators and the Trimmable Horizontal Stabilizer (THS), utilizing the green and yellow hydraulic systems.

Info via Ashraf Yehia, Aircraft Structure Repair Engineer