What happened
On 4 April 2021, a Reims Cessna F406, registration G-FIND, was conducting an unpressurised aerial photography mission over Northamptonshire. The flight, operated by a single pilot and one task specialist, involved flying parallel lines at 12,000 ft to capture images via a camera system mounted in the fuselage. While the pilot utilised portable supplementary oxygen, the task specialist did not, following company guidance that oxygen was unnecessary below 13,000 ft.
At approximately 1125 UTC, the task specialist reported feeling unwell and lost consciousness, falling into the aircraft aisle. The pilot declared an emergency and initiated a rapid descent. During the descent, the aircraft diverted to London Luton Airport. As the altitude dropped to 6,000 ft, the task specialist began to regain consciousness and was able to communicate with the pilot. By the time the aircraft reached 3,000 ft, the specialist had returned to their seat and was speaking normally. The aircraft landed at Luton without further incident, though the passenger was taken to hospital as a precaution.
The investigation
The AAIB examined the circumstances surrounding the loss of consciousness and the regulatory framework governing oxygen use. The investigation noted that the task specialist, who was fit and healthy with no known medical history, recalled feeling dizzy and sweaty shortly before the event. While medical tests at the hospital found no underlying cause for the episode, the investigators considered the possibility of hypobaric hypoxia or a predisposition to fainting exacerbated by altitude.
Findings
- The exact cause of the loss of consciousness could not be definitively established.
- Hypoxia was considered a possible contributing factor, although it is unusual for a healthy individual to lose consciousness at 12,000 ft without significant hyperventilation.\n- The operator's manual had previously categorised task specialists as 'additional crew,' exempting them from oxygen use below 13,000 ft, which differed from the more stringent requirements found in Part-SPO regulations.
Safety action
- The operator has updated its Operations Manual to mandate that all Task Specialists and Survey Operators must use supplementary oxygen during all unpressurised flights above 10,000 ft.