What happened
On 5 December 2019, a Cessna C208B, registration PK-BVN, was operating a scheduled passenger flight from Kisar to Kupang. The aircraft was carrying two crew members and 12 passengers. While cruising at 10,000 feet, the crew engaged in a discussion regarding a personal health matter. Following this conversation, the Second in Command (SIC) began to experience significant anxiety and shortness of breath.
As the SIC became increasingly distressed by the lack of supplemental oxygen on board, his physical condition deteriorated. He experienced dizziness, tunnel vision, and eventually lost consciousness for approximately 20 seconds. Recognizing the emergency, the Pilot in Command (PIC) declared a MAYDAY and requested an immediate diversion to Dili, Timor-Leste, which offered a shorter flight duration. The PIC also requested emergency medical services to be on standby for their arrival. The aircraft landed safely at Dili, and the SIC was transported to a local hospital for evaluation.
The investigation
The investigation examined the physiological state of the crew, the aircraft's equipment, and the operational procedures of the operator. Investigators found that while the aircraft was not equipped with supplemental oxygen, such equipment was not legally required for unpressurized operations below 10,000 feet. Medical examinations of the SIC following the event revealed normal blood pressure, oxygen levels, and heart rate, with no underlying physiological pathology found. However, the investigation noted that the SIC had been experiencing significant sleep deprivation and emotional stress related to family health issues in the week preceding the flight.
Findings
- The crew's discussion of a stressful health topic triggered acute anxiety in the SIC.
- This emotional stress led to hyperventilation, which, combined with the lower air density at cruising altitude, caused the pilot to experience tunnel vision and a brief loss of consciousness.
- The aircraft was operating within its legal requirements regarding altitude and oxygen availability.
Safety action
- The KNKT recommended that Susi Air review and update its serious incident reporting procedures to ensure more timely notifications to the investigation committee.
- A recommendation was issued to provide flight crew awareness training regarding how unmanaged emotional stress and hyperventilation can lead to pilot incapacitation in high-altitude environments.