What happened
On March 26, 2010, a Jodel DR 221, registration F-BPRT, was conducting a training flight at Saint-Cyr-l’Ecole when the instructor detected exhaust odors in the cockpit. Approximately one minute after takeoff, the aircraft's carbon monoxide detector indicated a positive reading.
The instructor, having confirmed that the cabin heating system was turned off, opened the external air vents to ventilate the cockpit. After notifying air traffic control, the pilot performed a turn and executed a precautionary landing on runway 29R. During the taxi to the parking area, the pilot slightly opened the canopy to further assist ventilation. No medical incapacitation occurred during the flight.
The investigation
The investigation examined the aircraft's systems and maintenance history. It was noted that on the previous day, a similar occurrence had been observed during ground engine tests, though the detector had returned to its original color after the engine was shut down. A new detector had been installed prior to the flight in question.
Ground inspections confirmed that the cabin heating system was functioning correctly and was not a source of exhaust leakage. However, investigators identified that two openings under the fuselage, which accommodate the exhaust muffler attachment brackets, were not sealed with silicone. This lack of sealing allowed exhaust gases to leak through the small openings and migrate into the cabin.
Findings
- The primary cause of the carbon monoxide detection was the absence of sealant on the two orifices used for the exhaust muffler attachment brackets.
- This lack of airtightness allowed exhaust gases to escape from the exhaust manifolds and enter the aircraft cabin.
- The aircraft had recently undergone a 2,000-hour inspection and fabric re-covering, following which the club had installed a carbon monoxide detector in compliance with DGAC recommendations.