What is the Airbus ‘Icarus Bug’ and how are airlines fixing it?
It involves a rare failure in a flight-control computer that can occur when high-energy radiation from the Sun interferes with onboard electronics
The "Icarus Bug" is the name given to a vulnerability found in several Airbus A320-family aircraft.
It involves a rare failure in a flight-control computer that can occur when high-energy radiation from the Sun interferes with onboard electronics.
The issue came to attention after an October incident in which an aircraft flying between the United States and Mexico suddenly lost altitude.
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Airlines are now carrying out repairs under the Icarus A32F Airworthiness Directive.
How does the bug work?
The problem centers on the way intense solar radiation can affect the data used by software that calculates the plane's elevation, says BECA (Belgian Pilot Association).
At high altitudes, cosmic rays—high-energy particles from the Sun and distant space—can penetrate aircraft and strike sensitive parts of computer chips. In some cases, this can cause a bit flip, which is when a stored "0" turns into a "1," or vice versa. In technical terms, this is called a single event upset (SEU).
Investigators found that ELAC B units (Elevator & Aileron Computers) running software version L104 were more likely to be affected. If corrupted data is fed into the flight-control system, the aircraft's elevators could move unexpectedly. In a worst-case situation, this could push the aircraft close to or beyond safe structural limits.
Why was it dangerous?
A single bit of wrong data inside a flight computer can cause incorrect readings or unexpected flight-control behavior. At cruising altitude, exposure to cosmic radiation is higher than at ground level, making this type of error more likely.
The October event, which involved a sudden altitude loss, increased concern that the vulnerability could put passengers and crew at risk if not corrected.
Which aircraft were affected?
The vulnerability affects the Airbus A320 family of planes, including:
- A318
- A319
- A320
- A321
About 6,000 aircraft worldwide were initially believed to be at risk.
How are airlines fixing the issue?
Airlines were given two repair options:
- Software reversion
Most aircraft—about 5,100—can be fixed by reverting to a previous, stable version of the flight-control software. This process takes about three hours per plane. - Hardware replacement
Older aircraft—around 900 to 1,000—require the physical replacement of the ELAC B computer with a unit running the earlier software. These aircraft cannot carry passengers until the replacement is completed.
Why does cosmic radiation affect aircraft electronics?
Cosmic radiation consists of high-energy particles from the Sun and deep space. On the ground, the Earth's atmosphere and magnetic field protect people and electronics from most of this radiation. At typical cruising altitudes, however, the air is much thinner, and aircraft computers are more exposed.
Cosmic rays can affect electronics in three main ways:
- Transient error (Single Event Upset) – a temporary bit flip caused by a particle hitting a chip.
- Minor component damage – small but recoverable degradation.
- Permanent damage – irreversible harm that requires hardware replacement.
Aircraft designers have been required to consider these risks since 2007, but the Icarus Bug shows that vulnerabilities can still appear when specific software or hardware combinations react unexpectedly to solar activity.
