If you’ve spent any time looking at the Minimum Equipment List (MEL) for the A320, you’ll notice a curious asymmetry. While you can often dispatch with ELAC 1 inoperative (under specific conditions), ELAC 2 is a hard “NO GO.”
To understand why, we have to look past the day-to-day “Normal Law” flying and dive into the nightmare scenario every Airbus pilot trains for: the Emergency Electrical Configuration (ELEC EMER CONFIG).
The Core Architecture: The 8-Second Gap
The primary reason ELAC 2 is mandatory for flight is a design characteristic of the aircraft’s transition into emergency power. If the aircraft loses both main generators (GEN 1 and GEN 2), it initiates the deployment of the Ram Air Turbine (RAT).
The RAT is a small windmill that drops into the slipstream to provide hydraulic pressure and electrical power. However, it isn’t instant. There is a critical window of approximately 8 seconds between the initial power loss and the RAT reaching full speed.
Pitch Authority and the “Hydraulic Trap”
During those 8 seconds of “darkness,” the aircraft is powered solely by its batteries. The system logic is split to ensure redundancy:
- Battery 1: Powers ELAC 1 and SEC 1.
- Battery 2: Powers ELAC 2 and the Trimmable Horizontal Stabilizer (THS) Motor 1.
The problem lies in which hydraulic systems these computers control. ELAC 1 controls the elevators via the Blue hydraulic system. However, in this emergency, the Blue system is pressurized only by the RAT. Since the RAT takes 8 seconds to spin up, the Blue system has zero pressure during the transition.
If ELAC 2 is inoperative, the aircraft effectively has no elevator control during those 8 seconds because the only active computer (ELAC 1) is trying to move surfaces with a “dead” hydraulic system.
The Backup to the Backup
You might wonder if the Spoiler Elevator Computers (SECs) could help. While SEC 1 and 2 can provide backup pitch control, they are also subject to the same electrical/hydraulic limitations during that transition period.
Why ELAC 2 is the “Chosen One”
ELAC 2 is wired to the Green and Yellow elevator actuators. Even with the engines off, these systems retain residual pressure in their accumulators (typically 3000 psi). This residual pressure is enough to maintain pitch control during the 8-second RAT deployment gap.
Because ELAC 2 is the only computer that can utilize this residual pressure while being powered by Battery 2, losing it means losing the ability to keep the nose up if the lights go out.
Modern Context: The “Solar Radiation” Software Issue
In more recent technical bulletins (2024–2026), ELAC 2 has faced additional scrutiny due to a specific software vulnerability. Research and real-world incidents (like a notable JetBlue event) revealed that intense solar radiation at high altitudes could occasionally corrupt the memory of the ELAC 2 computer.
Critical Fault: This corruption can lead to uncommanded pitch-down movements without triggering a “Fault” light. Because ELAC 2 is the primary computer for pitch, its failure to “self-diagnose” in this scenario is extremely dangerous.
Airbus and EASA have issued Airworthiness Directives (ADs) requiring software upgrades or hardware realignment. This recent history has only reinforced the strict “NO GO” status of ELAC 2; the system is so fundamental to the aircraft’s stability that any doubt about its integrity grounds the plane.
