To Russia with Love (1) - S3-E24
Character mistake: While talking with Falcon, Harm mentions the "green book" Falcon stole that listed all of the American POWs transferred to Russia after the Vietnam War. But when Harm originally found the book in "Ghost Ship", its cover was yellow.
Chosen answer: When landing on an aircraft carrier, a pilot "calls the ball" by confirming to the landing signal officer (LSO) that they have the carrier, and more specifically its landing guidance systems in sight. Carriers use a Fresnel lens system which is a light only visible at a certain angle, so if a pilot sees the "ball" they are at the correct altitude and glide slope for landing.
Sierra1 ★