What happened
Probable cause
Contributing factors
- The aircraft entered Jerusalem Bay, a known confined area, below terrain height with a level or slightly descending flight path. There was no known operational need for the aircraft to be operating in the bay.
- While conducting a steep turn in Jerusalem Bay, it was likely that the aircraft aerodynamically stalled at an altitude too low to effect a recovery before colliding with the water.
- It was almost certain that there was elevated levels of carbon monoxide in the aircraft cabin, which resulted in the pilot and passengers having higher than normal levels of carboxyhaemoglobin in their blood.
- Several pre-existing cracks in the exhaust collector ring, very likely released exhaust gas into the engine/accessory bay, which then very likely entered the cabin through holes in the main firewall where three bolts were missing.
- A 27 minute taxi before the passengers boarded, with the pilot’s door ajar likely exacerbated the pilot’s elevated carboxyhaemoglobin level.
- It was likely that the pilot's ability to safely operate the aircraft was significantly degraded by carbon monoxide exposure.
- Disposable chemical spot detectors, commonly used in general aviation, can be unreliable at detecting carbon monoxide in the aircraft cabin. Further, they do not draw a pilot's attention to a hazardous condition, instead they rely on the pilot noticing the changing colour of the sensor.
- There was no regulatory requirement from the Civil Aviation Safety Authority for piston-engine aircraft to carry a carbon monoxide detector with an active warning to alert pilots to the presence of elevated levels of carbon monoxide in the cabin. (Safety issue)
Other factors that increased risk
- It was likely that the effectiveness of the disposable carbon monoxide chemical spot detector fitted to the aircraft was reduced due to sun bleaching.
- Although detectors were not required to be fitted to their aircraft, Sydney Seaplanes had no mechanism for monitoring the serviceability of the carbon monoxide detectors. (Safety issue)
- The in situ bolts used by the maintenance organisation to secure the magneto access panels on the main firewall were worn, and were a combination of modified AN3-3A bolts and non-specific bolts. This increased the risk of the bolts either not tightening securely on installation and/or coming loose during operations.
- The operator relied on volunteered passenger weights without allowances for variability, rather than actual passenger weights obtained just prior to a flight. This increased the risk of underestimating passenger weights and potentially overloading an aircraft.
- The standard passenger weights specified in Civil Aviation Advisory Publication (CAAP) 235-1(1) Standard passenger and baggage weights did not accurately reflect the average weights of the current Australian population. Further, the CAAP did not provide guidance on the use of volunteered passenger weights as an alternative to weights derived just prior to a flight.
- Australian civil aviation regulations did not mandate the fitment of flight recorders for passenger-carrying aircraft under 5,700 kg. Consequently, the determination of factors that influenced this accident, and other accidents, have been hampered by a lack of recorded data pertaining to the flight. This has likely resulted in the non-identification of safety issues, which continue to present a hazard to current and future passenger-carrying operations. (Safety issue)
- Annex 6 to the Convention of International Civil Aviation did not mandate the fitment of flight recorders for passenger-carrying aircraft under 5,700 kg. Consequently, the determination of factors that influenced this accident, and numerous other accidents have been hampered by a lack of recorded data pertaining to the flight. This has likely resulted in important safety issues not being identified, which may remain a hazard to current and future passenger carrying operations. (Safety issue)
Other findings
- It was very likely that the middle-row right passenger did not have his seatbelt fastened at the time of impact, however, the reason for this could not be determined.
- The accident was not survivable due to the combination of the impact forces and the submersion of the aircraft.
- The pilot had no known pre-existing medical conditions that could explain the accident.