Investigation Summary
The accident highlighted a specific logic conflict within the Airbus A320's fly-by-wire system. During the final approach, the aircraft was subjected to vertical gusts and a tailwind that caused the angle of attack (AoA) to fluctuate rapidly. As the pilots pulled back on their sidesticks to arrest a high sink rate, the flight control computer calculated a 'predicted' AoA based on the current value and the rate of change. Because the pilots were pulling back hard while the aircraft was already experiencing high AoA due to windshear, the computer activated Alpha Protection. Once active, the system prioritized stall prevention over pilot pitch commands. Furthermore, because both pilots were making simultaneous 'dual inputs' without one pilot taking priority, the computer summed their inputs, further increasing the calculated rate of change and reinforcing the software's decision to limit nose-up pitch. The system also attempted to dampen perceived phugoid oscillations by pitching the nose down as the airspeed dropped due to the tailwind, directly opposing the crew's efforts to flare.
Final Conclusions
The CIAIAC concluded that the cause was the activation of the angle of attack protection system under a specific combination of vertical gusts, windshear, and simultaneous sidestick inputs not accounted for in the original design. This logic prevented the aircraft from pitching up and flaring. The investigation resulted in four safety recommendations and led Airbus to modify the flight control software to prevent the stall protection from being triggered solely by a high rate of change in the angle of attack when the aircraft is close to the ground.
Video Analysis
When Automation Goes Horribly Wrong | The Crash Of Iberia 1456 — A detailed breakdown of how the Airbus A320's Alpha Protection logic inadvertently caused a crash landing by overriding pilot inputs during a windshear encounter.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Seated in the left seat, supervising the flight.
First Officer
Seated in the jumpseat for this leg, having given his seat to the trainee.
Trainee Pilot
Pilot Flying (PF), seated in the right seat under supervision for line training.
Systems & Failure Modes
Alpha Protection (AoA Protection)
A flight envelope protection law that prevents the aircraft from exceeding a safe angle of attack. In this case, it incorrectly triggered a nose-down command during a critical landing flare.
Sidestick Priority System
In the A320, if both pilots move their sticks, the inputs are algebraically summed unless one pilot presses a priority button. The lack of priority assignment contributed to the high rate-of-change values seen by the computer.
GPWS (Ground Proximity Warning System)
The system provided 'Sink Rate' alerts, which prompted the crew to attempt a go-around seconds before impact.
Interesting Facts
- 01The aircraft was an Airbus A320-214 named 'Ciudad de Melilla', delivered to Iberia just one year prior to the accident.
- 02All 143 occupants survived; 25 people were injured during the evacuation, consisting of 1 serious injury (a female passenger) and 24 minor injuries (including one crew member).
- 03The Alpha Protection logic was designed to prevent stalls but did not account for the specific rate-of-change values generated by extreme windshear and dual pilot inputs.
- 04The aircraft was written off due to substantial structural damage to the fuselage and landing gear.
- 05The investigation by the CIAIAC took 5 years and 9 months to complete, with the final report released in November 2006.
Safety Actions & Advisories
Flight Control Software Modification
Airbus modified the flight control software logic to prevent Alpha Protection from being activated solely by a high rate of change in the angle of attack, particularly in the landing phase.