What happened
On April 4, 2011, a United Airlines Airbus A320-232, registration N409UA, was performing an emergency landing at Louis Armstrong New Orleans International Airport (MSY) following an avionics smoke warning. The flight had originally departed MSY for San Francisco but was forced to return shortly after takeoff.
During the after-takeoff checklist, the captain identified an avionics smoke ECAM (Electronic Centralized Aircraft Monitoring) message. While the crew did not detect the smell of smoke, the captain began the smoke checklist. During the procedure, the captain switched off generator two before manually deploying the ram air turbine (RAT), which caused the aircraft to enter an emergency electrical configuration. This transition caused a brief power interruption to the cockpit voice recorder and flight data recorder.
As the aircraft continued its descent in instrument meteorological conditions (IMC), the first officer lost his flight instrument displays, necessitating the captain taking control of the aircraft. The crew failed to perform several critical tasks, including an approach briefing, tuning navigation radios, or checking the ECAM status page to identify inoperative systems.
Upon landing on runway 19, the aircraft experienced a loss of reverse thrust on engine two. The aircraft veered to the left and departed the left side of the runway approximately 5,000 feet from the threshold, with the nose gear sinking into soft ground. An emergency evacuation was conducted. There were no injuries to the 104 passengers or the flight crew, though the aircraft sustained minor damage.
The investigation
Investigators examined the aircraft's electrical system and found that the emergency generator operates only with the landing gear retracted. The investigation confirmed that the crew lowered the landing gear while the aircraft was still operating on battery power, which prevented the restoration of electrical power via the generators.
Testing of the Cerberus Model CG7GO ionic smoke detector revealed that while the unit met all functional requirements, such detectors are sensitive to ambient temperature, pressure, and moisture. The investigation noted that the aircraft had experienced similar false warnings in humid environments previously.
An examination of the 1R emergency evacuation slide revealed that the sea anchor had become unfastened and was ingested by the slide's aspirator during deployment, which contributed to the slide's malfunction.