Elevated CO levels likely resulted in shark patrol crew’s partial incapacitation

Flight path

Key points:

  • All crew members began feeling unwell on second flight of the day
  • Pilot observed indications of elevated levels of CO on chemical spot detector
  • Crew immediately opened windows and confirmed cabin heating was off, but their condition deteriorated
  • The pilot alerted air traffic control and landed safely as soon as possible

The crew of a Cessna 172 conducting an aerial shark patrol experienced symptoms associated with carbon monoxide exposure, highlighting the dangers of this colourless and odourless gas found in piston-engine aircraft exhausts, an ATSB investigation notes.

The aircraft with a crew of three, comprising a pilot, communications officer and observer, had departed Adelaide’s Parafield Airport for a second aerial shark patrol at 1.30 pm on 22 December 2019.

While overhead Sellicks Beach, about two hours into the flight, the communications officer and then the pilot became sick. They initially dismissed their symptoms as being due to turbulence, but the pilot subsequently observed a localised discolouration on the aircraft’s disposable carbon monoxide chemical spot detector. The communications officer, in the front right seat, confirmed the discolouration and the crew confirmed they were all feeling light-headed.

The crew immediately opened the aircraft’s windows and confirmed the heating was off, however the pilot’s condition worsened and they reported losing periods of time, loss of feeling in their legs, chest pains, and a tingling sensation in their hands.

With support from air traffic control, the pilot was able to return the aircraft to, and land safely at Parafield Airport, despite experiencing increased light-headedness and ongoing confusion.

On landing, the crew were then taken to hospital for medical examinations. Blood test confirmed they had mildly elevated carboxyhaemoglobin levels.

“Despite having only mildly elevated carboxyhaemoglobin levels, the crew’s physical symptoms and cognitive effects likely resulted from exposure to elevated CO levels in the aircraft cabin,” said ATSB acting Director Transport Safety Kerri Hughes.

“Owners and operators of piston-engine aircraft are strongly encouraged to install active warning CO detectors to alert pilots to the presence of CO before it adversely affects their ability to control the aircraft or become incapacitated,” said Ms Hughes.

“Further, once they experience any smell or sensation of illness pilots should check their CO detector, ensure cabin heat is off, open all fresh air vents and windows, and make a prompt decision to land using all available resources for assistance – such as contacting air traffic control – to do this safely.”

In this incident, the CO source within the aircraft could not be established, Ms Hughes noted. There were no indications of a potential exhaust leak prior to the flight and the post-flight testing found no fault with the aircraft. However, the most likely source of CO was from the aircraft.

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