What happened
On 3 February 2016, a DHC-8-4 and registration G-JECR, operating a commercial passenger flight from Birmingham to Aberdeen, experienced a sudden loss of cabin pressure. While climbing through Flight Level 170, the flight crew heard a mechanical noise followed by the sound of rushing air. The commander identified a pressurisation failure after observing a high rate of climb on the cabin altitude gauge and the illumination of a fault light on the overhead panel.
As the crew experienced physical symptoms including light-headedness, chest tightness, and tingling in the fingers, the commander ordered the use of oxygen masks and initiated an emergency descent. The aircraft descended to Flight Level 100, during which the crew declared a MAYDAY. In the passenger cabin, the crew noted changes in aircraft attitude and engine note but did not hear the initial mechanical noise. After reaching a safe altitude, the commander decided to divert the flight to Manchester Airport. The aircraft landed safely without further incident, and there were no injuries among the 54 passengers or 4 crew members.
The investigation
AAIB investigators examined the aircraft's systems and reviewed data from the Flight Data Recorder. The investigation focused on the integrity of the door seals and the functionality of the pressurisation components. While no structural defects were found in the door seals, the investigation involved the removal of the Cabin Pressure Controller module and the Outflow Valve for manufacturer analysis. Flight data confirmed that the cabin pressure warning on the Central Warning Panel did not activate, as the cabin altitude had not yet exceeded 10,400 feet at the time of the event.
Findings
- The investigation determined that the Outflow Valve was unserviceable due to internal wear and contamination.
- The faulty valve was the primary cause of the rapid depressurisation.
- Testing of the Cabin Pressure Controller module by the manufacturer revealed no defects.