Final Answer:
The statement that is not correct is (A) A tax on nighttime departures can increase social welfare.
Step-by-step explanation:
The correct statement is (B) Social marginal cost of an additional departure is the noise cost incurred by the residents from an additional flight departure. This is because the social marginal cost includes the private costs of the airport as well as the external costs imposed on the residents, which in this case is the noise disturbance. Therefore, the social marginal cost of an additional departure does include the noise cost incurred by the residents.
Statement (C) Too many flights depart in the evening relative to the social optimum is also correct. If the number of flights departing in the evening causes significant disturbance to residents, it indicates that there may be too many flights departing at night relative to what would be socially optimal.
Statement (D) The private marginal cost of an additional flight to the airport is less than the social marginal cost is also correct. The private marginal cost only considers the costs borne by the airport, which are typically lower than the social marginal cost that includes external costs like noise disturbance to residents.
However, statement (A) A tax on nighttime departures can increase social welfare is not correct. While a tax on nighttime departures could internalize the external costs of noise disturbance, it does not necessarily increase social welfare as it may lead to other unintended consequences such as reduced air traffic and economic activity.
Therefore, based on this information, statement (A) is not correct.