For a private pilot, when does a second class medical certificate issued to a 42-year-old pilot on July 15 expire?

A second class medical certificate for a private pilot who is 42 years old is valid for 24 calendar months after the month of the examination. In this case, the certificate was issued on July 15, which means it will be valid until the end of July in the second year following the issuance. Therefore, the expiration date will be July 31, two years later.

As per FAA regulations, the expiration of a medical certificate is calculated by considering the month in which it was issued; thus, the pilot's medical certificate will indeed expire on July 31, two years after the initial examination date. This conforms to the regulatory framework that governs medical certification periods based on the age of the pilot at the time of examination.