Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation.
On 16 August 2021, a flight instructor and student pilot prepared a Piper PA-28 aircraft for a training flight departing from Wagga Wagga Airport.
At about 0900 local time, during taxi and prior to take-off, the instructor opened the cabin heater vent to demist the cabin windows. At approximately 0930, during initial climb, with the student at the controls, the instructor began feeling slightly dizzy and unwell. They inspected the aircraft’s disposable carbon monoxide (CO) chemical spot detector and observed that it had darkened, indicating the presence of elevated CO levels in the cabin (Figure 1).
Figure 1: The aircraft’s CO spot detector during the flight (left) and after landing (right)
Source: Aircraft owner
The instructor immediately alerted the student to the indication, closed the cabin heater vent and opened the cockpit’s fresh air vents and storm window. Upon being alerted by the instructor, the student informed the instructor that they were not experiencing any symptoms of CO poisoning. The student continued to fly the aircraft while the instructor provided directions to return to the airport, where the aircraft was landed safely.
After landing, the instructor continued to feel the effect of CO poisoning and was taken to hospital for treatment and released soon after.
An inspection of the aircraft’s exhaust and cabin heater systems did not identify any defects. Prior to returning the aircraft to service, engine ground runs were carried out to determine cabin CO levels. During these runs, cabin CO levels were low at all power configurations and heater settings.
As a result of this occurrence, the owner of the aircraft is assessing the feasibility of installing active-alarm cockpit CO detectors throughout its fleet of piston-engine aircraft.
Carbon monoxide is a colourless, odourless and poisonous gas which is formed through the incomplete combustion of carbon-containing materials, including aviation fuel. The exhaust fumes from piston engines contain high concentrations of CO. The presence of dangerous CO levels within a confined aircraft cabin may not be detected until the occupants begin to develop physical symptoms such as nausea, headaches, dizziness, shortness of breath and blurred vision along with cognitive effects such as confusion and impaired judgement. ATSB Safety Advisory notice AO-2017-118-002 Are you protected from carbon monoxide poisoning? strongly advises that piston-engine aircraft be equipped with a digital cockpit CO detector with an active warning to alert pilots to elevated CO levels in the cabin.
If a pilot detects any abnormal odours or experiences symptoms consistent with CO poisoning, they should ensure that the cabin heat vent is closed, open all fresh air vents and windows and take action to land as soon as possible using all available resources for assistance.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.