SESK: Stuff Everyone Should Know · sesk.info/pilot-postflight-fill-tanks
If an airplane will sit unused for a while, why is it good practice to fill the fuel tanks?
To prevent water condensation inside the tanks.
- To improve engine cooling on the next flight
- To recalibrate the fuel gauges
- To prevent water condensation in the tanks ✔
Why: Air in a partly empty tank holds moisture that can condense into water. The AFH says filling the tanks before the airplane sits helps prevent that.
Huh, didn't know that: The AFH says the postflight walk-around should look for oil or fuel streaks near the cowling and fuel stains under the wings.
I filled my tanks before vacation so the airplane wouldn't sweat while I was gone.
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References
Answer: To prevent water condensation in the tanks. Air in a partly empty tank holds moisture that can condense into water. The AFH says filling the tanks before the airplane sits helps prevent that.
- Airplane Flying Handbook FAA-H-8083-3C, Chapter 2 www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/03_afh_ch2.pdf
If the airplane is going to be inactive, it is a good operating practice to fill the fuel tanks to prevent water condensation
Checked 2026-10-09.
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