What happened
On 16 October 2000, a Piper PA-28-161, registration G-LSFT, was performing circuit training at Bournemouth International Airport. While positioned on left base for Runway 26, the instructor began experiencing light-headedness and impaired vision. The student pilot observed the instructor's deteriorating condition and suspected he had lost consciousness. During this period, the aircraft's carbon monoxide detector indicated a high level of contamination.
In an attempt to mitigate the effects, the instructor requested that the student open the side window to allow fresh air into the cockpit. Although the crew notified Air Traffic Control of a carbon monoxide indication, communication became difficult. The instructor initially decided to land the aircraft in an open area near a river. During the maneuver, the instructor unbuckled his harness to lean toward the fresh air entering through the window. This action improved his physical state, allowing him to continue the approach to the airfield.
Air Traffic Control, observing a steep descent on the base leg, mistakenly believed the aircraft had suffered an engine failure and alerted the Airport Fire Service. The aircraft landed safely after the preceding aircraft had vacated the runway, though it came to a halt at a holding point. Upon exiting, the student pilot reported feeling disoriented. Emergency services provided oxygen to both crew members.
The investigation
Investigators examined the aircraft's heating and exhaust systems. While the firewall appeared secure and the muffler showed no visible cracks, a significant gap was discovered at the slip joint where the left front cylinder stack meets the muffler. Although pressure testing of the exhaust boxes revealed no faults, the 'scat' hose connecting the exhaust shroud to the cabin heat distributor box was found to have small pinholes.
Findings
- A significant gap existed at the slip joint of the exhaust system stack.
- Pinholes were present in the hose connecting the exhaust shroud to the cabin heat distributor.
- The cabin heater had not been active during the flight, yet contamination occurred.
- The instructor experienced physiological symptoms consistent with carbon monoxide exposure.