In aviation, a second officer is usually the third in line of command for a flight crew on a civil aircraft. In the past years of commercial aviation, a second officer would be used on international or long haul flights where more than two crew are required for the purpose of relieving other higher ranked crew members for adequate resting periods.

In some airlines, the second officer acts as a first officer, but still undergoes training and supervision from a training captain (Swiss International Air Lines, Lufthansa, Volotea among others use this denomination). Some major airlines in China also use this denomination including Air China and China Eastern Airlines.

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