What happened
At about 0800 local time on 1 June 2025, an instructor and student were conducting a training flight from Bankstown Airport, New South Wales in a Piper PA-28-151 aircraft. The aircraft was fitted with a disposable passive carbon monoxide (CO) detector.
During the pre-flight preparations, the CO detector was confirmed to show that there were no signs of carbon monoxide in the cockpit.
Shortly after take-off, while climbing through 300 ft, the instructor noticed that the CO detector had changed colour and was showing full black, indicating a high presence of carbon monoxide in the cockpit. This indication was then verified by the student pilot.
The instructor took over control of the aircraft and asked the student to open the storm window to allow fresh air into the cabin. At the advice of the instructor, the student placed their mouth and nose close to the storm window to breath from the stream of fresh air.
The flight crew requested, and ATC approved, the aircraft to rejoin the circuit and they landed back at Bankstown Airport shortly after with no further event. Prior to landing, the CO detector was noted to have changed colour to light brown, indicating that levels of carbon monoxide in the cockpit had reduced, likely due to the storm window being opened.
Once on the ground, the student pilot reported feeling no symptoms of carbon monoxide poisoning, while the instructor experienced only slight dizziness, but believed this could have been caused by adrenaline from managing the event. Blood tests conducted on both pilots detected only negligible levels of carbon monoxide in their bloodstreams.
A subsequent engineering inspection of the aircraft revealed a rubber boot seal on a nose wheel steering rod had split which was suspected of causing the CO leak. Following rectification, a check flight was performed during which no carbon monoxide was detected inside the cockpit.
Safety message
This incident serves as a salient reminder of the importance of carrying effective carbon monoxide (CO) detection equipment on board aircraft.
CO is a colourless, odourless and tasteless gas found in exhaust gases of piston engine aircraft. While passive CO detectors are commonly used in general aviation aircraft, they have limitations and rely on the pilot regularly monitoring the colour of the detector. In contrast, active electronic CO detectors are designed to attract attention through an audible alert at low CO concentrations, so are more likely to be effective. These devices are now inexpensive and widely available.
Following the fatal crash of a DHC-2 in 2017, in which the pilot was impaired due to carbon monoxide poisoning (Collision with water involving a de Havilland Canada DHC-2 Beaver aircraft, VH‑NOO, at Jerusalem Bay, Hawkesbury River, New South Wales, on 31 December 2017 AO-2017-118), and a review of the effectiveness of carbon monoxide detectors by the UK Civil Aviation Authority, the ATSB launched its Know CO campaign.
In addition, the Civil Aviation Safety Authority has published an Airworthiness Bulletin (AWB 02-064 Issue 5) on Preventing Carbon Monoxide Poisoning in Piston Engine Aircraft.
These resources highlight the limitations of passive carbon monoxide detectors and strongly recommend that operators and owners of piston engine aircraft install active attention‑attracting CO detectors which provide the best opportunity of detecting carbon monoxide exposure before it can adversely impact their ability to control the aircraft.
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.