What happened
On 12 October 2011, a Bombardier DHC-8-402 Dash 8, registration G-JECH, was performing a scheduled passenger flight from Manchester Airport to Brussels Airport. While the aircraft was descending from FL250 to FL200, the flight crew experienced a sudden drop in cabin pressure, which manifested as mild inner ear pain. This was immediately followed by a loud noise from the rear left galley area and the activation of the red CABIN PRESS warning light.
In response to the depressurisation, the crew donned oxygen masks and initiated an emergency descent. The commander declared a MAYDAY and set the transponder to 770 and requested a continuous descent to FL100. During the descent, the aircraft's rate of climb in cabin altitude exceeded 3,000 ft/min. The commander halted the descent at FL80, at which point the cabin pressurisation system was able to stabilise the cabin altitude at 2,000 ft. After confirming that the passengers were unharmed, the crew cancelled the emergency declaration and proceeded to land at Brussels Airport without further incident. There were no injuries to the 4 crew members or 49 passengers on board.
The investigation
The investigation established that the depressurisation was triggered by a split in the inflatable seal located on the aft baggage compartment door. This failure caused the blow-out panels on the bulkhead separating the baggage area from the passenger cabin to open. The resulting air leak allowed the passenger cabin to depressurise.
Following the event, maintenance personnel inspected the aircraft and confirmed that the inflatable seal on the cargo door had indeed split. The investigation noted that at the descent level of FL80, the rate of air leakage was low enough for the pressurisation system to maintain a stable cabin altitude of 2,000 ft.