What happened
On 7 June 2001, a Lockheed L188C, registration G-FIZU, was performing a public transport flight from Rennes, France, to Bordeaux. While climbing through FL40, the crew heard a loud bang followed by violent vibrations and a sudden loss of cabin pressure. The commander immediately declared a MAYDAY and initiated an emergency return to Rennes. After completing necessary emergency procedures, the aircraft performed a successful ILS approach and landed safely. Upon inspection at the airfield, it was discovered that the Crew Emergency Exit Door (CEED) was missing and the hinge mechanism had sustained damage.
The investigation
Although the event occurred in French airspace, the AAIB conducted the investigation. The investigation focused on the design and operation of the CEED, which had been installed as part of a freighter conversion via a Supplemental Type Certificate (STC). The door was located within the Forward Freight Door and was secured by two latches and a tensioning handle.
Investigators found that the cockpit's 'DOOR UNSAFE' warning light relied on a micro-switch that only triggered if the door was not flush with the frame. This meant that if door seals were worn or the fit was loose, the light could be extinguished even if the door was not actually locked. Furthermore, the specific door on G-FIZU lacked any markings or placards to indicate the locked or unlocked positions of the handle. The investigation also noted that the crew's regular aircraft used a different, more clearly marked locking mechanism, which could have contributed to confusion.
Findings
- The Crew Emergency Exit Door became detached during the climb.
- The aircraft's warning system could provide a false 'door safe' indication if the door was closed but not properly locked, particularly with worn seals.
- The lack of clear markings on the door's locking handle prevented the crew from easily verifying the door's security.
- There were no entries in the technical log regarding issues with the door warning system.
Safety action
Following the incident, the operator and maintenance organization implemented several measures, including applying placards to indicate handle positions, safety wiring the tensioning handle, and updating pre-flight checklists to include a physical verification of the door latches. The AAIB also issued recommendations to the CAA and FAA to ensure that door locking mechanisms are clearly marked and that warning systems accurately reflect the locked status of the door.