What happened
On 20 April 2004, a SD3-60 Variant 300, registration G-VBAC, was performing a cargo flight when the crew experienced a sudden and significant increase in ambient noise within the cockpit. While descending through approximately 4,000 feet toward Bournemouth, the crew observed that the overhead emergency escape hatch on the flight deck had detached from the airframe.
Despite the loss of the hatch, the crew reported that the aircraft's flight controls remained normal and engine indications showed no abnormalities. There was no audible or physical impact felt on the airframe during the separation. The crew immediately reduced airspeed and issued a PAN-PAN call to Bournemouth ATC. The aircraft completed a radar-assisted ILS approach to Runway 08 and landed without further incident. The only operational difficulty noted was the high noise level, which hindered communication with air traffic control. There were no injuries to the two crew members.
The investigation
The investigation focused on the mechanical state of the hatch and the events leading up to the separation. The flight deck hatch is secured by four shoot-bolt pins operated by an internal handle. To ensure a secure lock, the handle must be moved through an over-centre regime. If this final movement is not completed, the pins can migrate backward under pressure, eventually allowing the hatch to disengage.
Investigators discovered that during a cabin crew training session the previous day, the flight deck hatch had been operated for demonstration purposes. The instructor found the handle difficult to move through the final locking stage and was unable to fully engage the over-centre mechanism. Although the instructor notified a ground staff member that the hatch was not fully locked, the individual was not part of the engineering team and did not report the issue. Subsequent inspections of the aircraft aperture showed no damage, and the hatch itself was not recovered, presumably having fallen into the sea.
Findings
- The primary cause of the incident was that the escape hatch was not fully locked following a training demonstration.
- The difference between a secure and an insecure handle position was not visually obvious to the flight crew.
- The lock pins progressively moved out of position during the five flight sectors following the training session, allowing the airstream to pull the hatch away from the aircraft.
- A breakdown in communication occurred when the training instructor's report of an insecure hatch was not passed to the maintenance department.