What phrase should be used to remind aircraft to check their wheels down on approach?

Using the phrase "Check wheels down" is appropriate for reminding pilots to ensure their landing gear is deployed properly before landing. This phrase is clear and unambiguous, specifically directing the crew's attention to the condition of the wheels, which are critical for a safe landing.

In air traffic control communications, clarity is paramount, especially concerning safety-related checks. By using a direct reference to "wheels," the phrase emphasizes the importance of verifying the aircraft's landing gear position, which is crucial for preparing for a safe landing.

Other phrases, while related, may not convey the same specificity or clarity. For instance, "Prepare for landing" is more about the general action of getting ready to land rather than a specific check. "Check gear down" is a less common phrasing and can be interpreted in various ways. "Verify landing gear" may also come off as less direct compared to the chosen phrase. Thus, "Check wheels down" effectively fulfills the intent of providing a clear and direct reminder to pilots to confirm their landing gear position before landing.