What happened
On 6 December 2014, a Robin DR400-120, registration F-GOVA, was conducting a night VFR instruction flight near Cambrai, France. The aircraft was occupied by an instructor and two pilots participating in a night rating training session.
Shortly after passing 500 feet during the initial climb, the pilot in the front seat reported feeling unwell. Simultaneously, the instructor and the second pilot in the rear seat began experiencing similar symptoms. Despite experiencing physical difficulty, the instructor maintained control of the aircraft and performed a steep, 45-degree banked U-turn to return to the airfield for an emergency landing. To provide ventilation, the front pilot opened the cockpit canopy. The instructor successfully landed the aircraft on the runway without further damage, though he reported extreme lethargy and near-sleepiness upon touchdown.
The investigation
The investigation focused on the source of the physiological symptoms and the condition of the aircraft's heating system. During the pre-flight inspection, the instructor had noted that the carbon monoxide (CO) detection patch appeared darker than usual, though lighting conditions made a definitive assessment difficult.
Technical examination of the engine compartment revealed a leak at the ceramic seals of the exhaust pipe, caused by worn gland packing on the manifolds for cylinders 2 and 4. This allowed exhaust gases to escape into the engine compartment. Furthermore, investigators discovered that the flexible hose connection supplying hot air from the heat exchanger housing to the heating control box had been incorrectly swapped with the connection for the carburettor air inlet.
Findings
- The primary cause of the carbon monoxide poisoning was the inhalation of exhaust fumes through the windshield demisting system.
- A leak in the exhaust manifold assembly allowed gases to permeate the engine compartment.
- An error in the plumbing of the heating system, specifically the switching of two flexible hoses, directed contaminated air into the cockpit.
- The crew's ability to react quickly was aided by a pre-flight briefing in which the instructor had specifically instructed the crew to report any physiological symptoms immediately.