What happened
On 5 January 1999, a Boeing 737-436, registration G-DOCM, was performing a scheduled public transport flight from Helsinki to London Gatwick. During the descent from FL 270, the Commander initiated the Descent Check List. As the First Officer attempted to read the list, she began speaking incoherently. Shortly thereafter, she experienced a violent physical seizure, during which her body became rigid and she applied significant rudder input, causing a noticeable movement felt by passengers.
The Commander immediately disconnected the autopilot and neutralized the rudder. After declaring a MAYDAY and requesting priority landing, the crew managed the situation while descending. Cabin crew members arrived on the flight deck to provide oxygen and attempted to move the unconscious First Officer. Despite the difficulty of maneuvering her out of the seat without compromising the Commander's control of the aircraft, the crew successfully moved her to the forward galley to administer first aid.
The investigation
The investigation examined the medical event and the technical aspects of the approach. While the aircraft was being vectored toward Runway 26, air traffic control experienced a delay in providing descent clearance. This was due to the Processed Radar Display System producing a false emergency transponder return, which incorrectly suggested another aircraft was near G-DOCM. Technical analysis determined this was an isolated system error.
Findings
- The First Officer became incapacitated during the descent phase of the flight.
- The sudden physical movement of the First Officer caused an unintended and significant rudder application.
- The Commander successfully landed the aircraft at Gatwick without further incident.
- The radar delay was caused by a spurious transponder return on the radar display, which was deemed an isolated technical occurrence.