Important Note: This question has been created from incomplete feedback on Q 219689. We would very much appreciate any additional feedback to understand what exactly the question asks about, and how the answer options are presented as we are not sure any are entirely correct. Thank you!

EASA Learning Objectives:
021.10.02.01.01: Name the type of fuel used for petrol engines including its colour (AVGAS); 100 (green); 100LL (blue).
021.10.02.01.08: Describe the method and occasions for checking the fuel for water content.

Regardless of fuel type, fuel must be checked before the first flight of the day. PPL holders will be familiar with this. However, it is also highly advisable to sample fuel after refueling. Ideally, after a period of time to allow contaminants to settle to the sump from where the sample is taken. A period of 30 minutes would be approximately correct for a large fuel tank in a jet to ensure contaminants have settled, but a shorter time would be sufficient for smaller fuel tanks such as those in light aircraft.

Regarding the colour of each fuel type:

• AVGAS 100 is green.
• AVGAS 100LL is blue.
• Jet A-1 is clear or straw coloured.

There is only one answer that contains the correct fuel colour description. This is the only unambiguous part of the question.

When contaminated with water:

• AVGAS: The water will separate out from the fuel, and be visible as a clear liquid layer at the bottom of the sampler.
• Jet A-1: The clearer colour of Jet A-1 makes it much more difficult to see water contamination in the fuel. Usually these fuels are tested with other means than just visual examination to ensure they are free from water contamination. Although, because the water and fuel do not mix, it is still possible to see water contamination. If the fuel sample is examined before the water has settled, the fuel may appear cloudy.