What happened
On February 19, 2006, a Boeing MD-11F cargo flight departing from Dakar, Senegal, for Frankfurt, Germany, experienced a sudden and severe cabin pressure fluctuation during its climb. While the aircraft was ascending through approximately FL 250, the crew and a passenger on board experienced intense ear pain accompanied by a loud noise.
Upon checking the Engine and Alert Display (EAD), the crew observed a "Cabin Rate" alert. The cabin pressure control panel indicated that the outflow valve had opened significantly, resulting in a cabin pressure change rate exceeding 2,000 ft/min. Following the event, the crew elected to continue the flight to Frankfurt at a reduced cruising altitude.
While the co-pilot and a passenger sustained minor injuries, the captain suffered a severe barotrauma to the right inner ear. This injury resulted in permanent hearing loss and tinnitus, ultimately leading to the permanent loss of the captain's medical flight certification.
The investigation
The BFU investigation focused on the technical failure of the cabin pressure control system. Investigators examined the Cabin Pressure Controller, the Outflow Valve Motor Assembly, and the Cabin Pressure Sensor. The investigation also reviewed maintenance records, noting that several previous "Level 3" error messages had been recorded in the technical logbook but were marked as fixed following standard "Return to Service" tests.
Simulation models were utilized to analyze the pressure drop, though discrepancies were noted between the simulation parameters and the findings established by the BFU. The investigation also looked into the communication chain between the airline, the maintenance facility, and the component manufacturers.