What happened
On March 10, 2023, a flight student was conducting a solo navigation training flight from Billund to Roskilde in a Piper PA28-161, registration OY-JED. While cruising at approximately 2,300 feet over Sprogø, the pilot suddenly experienced dizziness, tunnel vision, and respiratory difficulties.
Because the student had experienced a similar incident a week prior—which was attributed to suspected carbon monoxide—the pilot initially believed carbon monoxide was present. The pilot noted that the cockpit's carbon monoxide indicator appeared to have changed to a brownish-red color. To mitigate the effects, the pilot opened the ventilation window, cracked the cabin door, and turned off the heating system. These actions led to an improvement in symptoms within one minute. After declaring an emergency and receiving support from air traffic services, the pilot proceeded to land safely at Roskilde Airport. Following the landing, the student was transported by ambulance to a hospital for observation and treatment with supplemental oxygen.
The investigation
The Danish Accident Investigation Board examined the aircraft's engine compartment and cabin. The technical inspection revealed that the engine was leaking oil at several points, specifically at the junction between the two engine blocks. Additionally, oil was found to have spilled onto part of the exhaust system. The investigation also identified several cracks in the air duct used for cabin and windshield heating.
Medical analysis of the student's bloodwork showed no evidence of carbon monoxide poisoning, as the levels were at zero. However, the findings indicated that the student's respiratory system had been affected, with physiological markers suggesting a period of oxygen deprivation or exposure to irritants. The investigation also noted that the carbon monoxide warning indicator was displaying an abnormal color pattern (sandy with black spots) that the manufacturer could not fully explain.
Findings
- The primary cause of the student's symptoms was the inhalation of engine oil vapors into the cabin.
- The engine's oil leaks and the cracks in the heating ductwork allowed vapors to enter the cockpit.
- The pilot's symptoms were initially misidentified as carbon monoxide poisoning due to a previous similar event and the unusual appearance of the CO indicator.
- There were no specific procedures or checklists available for this aircraft type and operation to manage the presence of toxic vapors or oil fumes in the cabin.