What happened
On 28 March 2023, the pilot of a Cessna 172N was taking-off from Groote Eylandt, Northern Territory. Shortly after setting take-off power, the engine ran rough and the pilot rejected the take-off. During the subsequent taxi, the engine failed. The post-flight inspection revealed water contamination in the aircraft’s fuel strainer.
During the daily inspection, the pilot had observed that the right fuel filler cap was unsecured and conducted fuel drains which revealed a quantity of water in the tank. The pilot drained further samples from the fuel tank until no further indications of water contamination were present.
The pilot then refuelled the aircraft and conducted further fuel quality checks which did not indicate the presence of water in the fuel system.
Safety message
Pilots should be vigilant in conducting fuel quality checks and may need to re-familiarise themselves with the fuel contamination settling times, especially in cases where contamination is suspected.
If contamination is detected in the fuel system during initial checks, pilots should thoroughly drain all drain locations again, starting at the highest drain location. If repeated samples indicate significant contamination, the aircraft should not be flown until maintenance action is undertaken.
Pilots should consult approved flight manuals and operator procedures to determine the correct procedure for fuel quality checks.
Filler caps and gaskets
Incorrectly installed and worn fuel filler caps and gaskets leave fuel systems vulnerable to contamination. Pilots should check caps for condition, proper sealing, security, and alignment before and after flight. Worn filler caps and gaskets should be replaced.
Agitation and settling time
After refuelling or moving an aircraft, pilots should allow extra time for fuel contaminants to settle toward the draining area. The Civil Aviation Safety Authority (CASA) has published Advisory Circular AC 91-25 – Fuel and oil safety which provides advice and guidance on procedures and practices to ensure the safety of fuelling operations.
Conducting a fuel drain immediately after fuelling or agitating the fuel tanks may not identify the presence of water and other contaminants. Fuel moving in the tank may disperse water and other contaminants which can remain suspended for some time.
When fuel contamination is suspected, pilots should allow for adequate settling time before testing for water. The CASA AC 91-25 provides suggested settling times for different aviation fuel grades.
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.