Incident Overview
On 19 April 2012 at 17:20 UTC, Brussels Airlines flight BEL2YB, a BAe Avro RJ100, departed Brussels for a scheduled passenger flight to Stockholm Broma. Fifteen minutes after takeoff, the crew received a master caution with both white and amber pressurization captions on the central warning panel. Following the checklist, the crew switched to manual pressurization control. They contacted Maastricht UAC to report the pressurization problem and request a descent. Initial clearance to FL260 was given. The pilots insisted on a lower altitude, receiving clearance to FL250, but the cabin altitude exceeded 9,000 feet and continued climbing. Without immediate clearance, the crew declared a mayday. Further descent to FL100 with radar vectors was provided, and the cabin altitude warning horn activated. The flight crew donned oxygen masks and alerted the cabin crew for an emergency descent. After leveling at FL100, the aircraft returned to Brussels. Post-flight, a pressurization test in the hangar revealed a major leak due to a 1089 mm crack in the left-hand aft fuselage skin. Additional cracks were found in frames 41X and 42.
Findings
The investigation determined that the incident was caused by a crack of 1089 mm in the left-hand aft lower skin panel, located in the lap joint area below the aft toilet servicing door. The fracture resulted from multiple origin fatigue crack propagation that initiated in the chemical etched channel on the external surface of the skin panel. A hazard identified was structural weakness not covered by existing fatigue inspections.
Safety Actions
On June 13, 2013, BAe Systems issued inspection service bulletin 53-239, requiring internal low frequency eddy current inspection of aft fuselage skin panels at stringer 30, between frames 39Y and 44, and detailed visual inspection of frames 41, 41X, 42, and 43 from stringer 29 to 31. This bulletin was mandated by EASA AD 2012-0178, effective September 21, 2012, with compliance periods based on flight cycles. Subsequently, EASA AD 2012-0184 superseded it on September 12, 2012, reducing compliance times for aircraft with 9,000 or more flight cycles from 6 months to 1 month. The Air Accident Investigation Unit (AAIU) of Belgium supports these actions and has no further recommendations to BAe Systems.
Investigation Status
The AAIU has gathered all operational and engineering information and is finalizing the investigation. A full report is expected within the next months. This interim report is issued to comply with Annex 13 and EU Regulation 996/2010, which require a safety investigation report or interim statement within 12 months of the incident.