What happened
On August 7, 2012, a Boeing 757-21B, registration G-LSAH, operated by Jet2.com, was performing a charter flight from Tenerife South Airport to Leeds Bradford Airport. During the climb through FL 230, the flight crew received a "CABIN ALT" warning on the EICAS, indicating a loss of cabin pressure. The cockpit altimeter showed a rapid increase in cabin altitude, climbing toward 15,000 ft.
The crew immediately donned oxygen masks and initiated an emergency descent to 10,000 ft. While the descent was executed according to procedures, the passenger oxygen masks failed to deploy for several rows, requiring flight attendants to manually move passengers to areas where masks were functional. To manage the aircraft's weight for an overweight landing, the crew performed a fuel-burning maneuver by flying with the landing gear extended and spoilers deployed.
After circling to reduce weight, the aircraft returned to Tenerife South Airport and landed safely. There were no fatalities and no injuries among the 222 passengers or 7 crew members.
The investigation
The CIAIAC investigation focused on the cause of the depressurization and the maintenance actions performed prior to departure. Investigators examined the aircraft's wastewater system, the flight recorders, and the maintenance logs.
It was discovered that prior to takeoff, a maintenance technician had identified a detached drain valve in the aft bathroom service panel. To avoid delaying the flight, the technician removed the deteriorated valve entirely rather than following established repair or deferral procedures. Subsequent inspections at the airline's main base revealed that the depressurization occurred through the area where the valve had been removed, as the remaining system had not been properly isolated.
Findings
- The primary cause of the depressurization was an air leak through the area of the removed bathroom drain valve.
- The maintenance technician performed an undocumented repair that was not authorized by the Aircraft Maintenance Manual (AMM) or the Structural Repair Manual (SRM).
- The technician acted under self-induced pressure to prevent flight delays and failed to follow the proper Minimum Equipment List (MEL) process for deferring the malfunction.
- The flight crew accepted the aircraft for dispatch without verifying if the maintenance action complied with the MEL.
- Corrosion had caused the original valve to deteriorate.
- Deficiencies in communication technology and technical information availability at the Tenerife station contributed to the improper maintenance decision.