Which statement about 24-month checks is correct?

• A. They are optional and rarely performed
• B. They focus on propeller balance
• C. They require flight time logs to be reviewed
• D. They include inspection of the transponder

Answer: (D)

A 24-month check is a mandated maintenance interval that includes verifying the transponder’s operation. The transponder is checked to ensure it responds correctly to ATC interrogations and encodes altitude properly, providing reliable radar identification and altitude information. This keeps air traffic services accurate and safe, which is especially important in instrument conditions where separation relies on this equipment. It’s not about propeller balance, and while maintenance history and logbook entries are part of the overall process, the defining requirement of this interval is the inspection and verification of the transponder.