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The drain valve on an aircraft fuel system is used:
  • A
    To empty the tanks during maintenance.
  • B
    To vent the tanks in case of overpressure.
  • C
    To remove particles from the fuel.
  • D
    To take a fuel sample and check its quality.

Refer to figure.

Each fuel tank is equipped with a drain valve located at the lowest point in the tank. This drain allows the pilot during preflight walk-around to check for and drain off any water which may have accumulated in the fuel tank.

  • Hydrocarbon fuels tend to absorb water, and such water will precipitate out of the fuel when its temperature drops. There is therefore a likelihood of some water collecting in aircraft fuel tanks, despite all possible precautions being taken to maintain the quality of fuel up to the point of it being pumped into the aircraft.

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