What happened
On May 14, 2017, a Boeing 737-600 departed from Prague, Czech Republic, bound for Djerba/Zarzis, Tunisia. While climbing through flight level 320, the aircraft experienced a sudden loss of cabin pressure. The depressurization was significant enough to trigger the automatic deployment of passenger oxygen masks.
The flight crew immediately donned their own oxygen masks and initiated an emergency descent to flight level 100. During the descent, the crew notified Munich Radar of the emergency and was cleared to descend. The pilots elected to divert to Munich Airport for an emergency landing. The aircraft arrived at Munich and landed safely on runway 26 L at approximately 10:05 UTC. There were no injuries to the passengers or crew, and no damage was reported to the aircraft or surrounding property.
The investigation
The BFU examined the aircraft's flight data recorder (FDR) and cockpit voice recorder (CVR). The investigation focused on the mechanical cause of the pressure loss and the performance of the cabin pressure control systems. Investigators also reviewed the maintenance history and the aircraft's airworthiness status.
Findings
Technical inspections revealed that the primary cause of the depressurization was a leak in the transition area between the APU and the cabin, specifically involving a bulk seal on the APU bleed duct. This leak was caused by a loose clamp that had shifted from its correct position. Additionally, investigators identified a secondary leak in the left-hand (L/H) pack.
Data from the Cabin Pressure Controllers (CPC) confirmed a "High Cabin Air Leak Rate," noting that the cabin pressure rate had exceeded 2,000 feet per minute. Following the incident, the aircraft was repaired; after addressing the leaks, the aircraft was cleared for a ferry flight without passengers up to flight level 250 in accordance with the Minimum Equipment List (MEL).