Final answer:
Two white flashes followed by one green flash from an airport beacon indicates that the airport is open.
Step-by-step explanation:
An airport beacon that emits two white flashes and one green flash is used to indicate the status of an airport. This specific sequence of flashes signals that the airport is open to air traffic. It's important for pilots to be familiar with these signals for safe navigation, especially during the hours of operation at night or when visibility is poor. An airport beacon with a different sequence, such as alternating white and green flashes, would have a different meaning, which is why it is crucial to understand and correctly interpret the airport beacon codes.