Investigation Summary
The accident flight was the final leg of a 'fly-and-dine' charter. Prior to the accident, the pilot had taxied the aircraft for approximately 27 minutes with the engine running and the pilot's door ajar while waiting for another aircraft to clear the pontoon. Investigators believe this extended taxi period significantly contributed to the pilot's elevated carboxyhaemoglobin (COHb) levels. Post-mortem toxicology revealed COHb levels of 11 percent in the pilot and between 8 percent and 11 percent in the passengers. The source of the CO was traced to several pre-existing cracks in the engine's exhaust collector ring. The gas entered the cabin through the main firewall via three missing bolts on the magneto access panels. Although the aircraft was equipped with a disposable chemical spot CO detector, it was found to be potentially unreliable due to sun bleaching and the fact that it required active monitoring by the pilot rather than providing an audible alert.
Final Conclusions
The ATSB final report, released on 28 January 2021, concluded that the pilot's ability to safely operate the aircraft was significantly degraded by carbon monoxide exposure. The investigation identified safety issues regarding the unreliability of disposable CO detectors and the lack of regulatory requirements for active CO warning systems in piston-engine aircraft. The report also noted that the maintenance of the firewall was inadequate, as the missing bolts allowed exhaust gases to bypass the engine bay and enter the passenger cabin.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
44-year-old Canadian-Australian pilot Gareth Morgan.
Systems & Failure Modes
Engine Exhaust System
The exhaust collector ring had pre-existing cracks that allowed exhaust gases to leak into the engine accessory bay.
Firewall Access Panels
Magneto access panels on the main firewall were missing three bolts, allowing CO-rich air to enter the cockpit and cabin.
CO Detector
A disposable chemical spot detector was present but lacked an active alarm and was likely degraded by sun exposure.
Interesting Facts
- 01The aircraft was 54 years old and had been completely rebuilt in 1996 after a previous fatal crop-dusting accident near Armidale, NSW, while registered as VH-IDI.
- 02Toxicology reports showed the pilot had a carboxyhaemoglobin (COHb) level of 11 percent, and passengers between 8 and 11 percent.
- 03Three bolts were missing from the magneto access panels on the engine firewall, providing a path for exhaust gases into the cabin.
- 04The aircraft was not equipped with an active (audible) carbon monoxide detector, only a disposable chemical spot detector.
- 05The DHC-2 Beaver was not fitted with a stall warning system, which was not required under Australian regulations at the time.
- 06The pilot taxied the aircraft for 27 minutes with the door ajar prior to the accident flight, likely increasing CO exposure.
Safety Actions & Advisories
Active CO Detector Fitment
Sydney Seaplanes fitted all aircraft with active electronic CO detectors and incorporated serviceability checks into monthly checklists.
Maintenance Classification
The removal and installation of firewall access panels was reclassified as a critical maintenance task requiring specific certification and conformity inspection.
Mandatory CO Testing
Maintenance providers were directed to conduct mandatory CO testing following any work on the engine exhaust system or firewall panels.
Recurring Inspection Program
An inspection of the magneto access panels and CO testing was incorporated into the 100-hourly 'B' check inspection.
Known Controversies & Unanswered Questions
Stall Warning System Mandates
Reference ↗Following the accident, the lack of a stall warning system became a point of discussion. While the TSB of Canada had previously recommended mandating these systems for all commercial DHC-2 operations, Transport Canada determined in 2019 that there was insufficient justification for a mandate, citing that in certain configurations the aircraft provides so little natural warning that a system might not provide enough time for recovery.