(Jerry Jackson/The Baltimore Sun via AP) RICHMOND, Va. (CN) — The en banc Fourth Circuit appeared split Monday on the constitutionality of a Baltimore police surveillance program under which as much as 90% of the city was observed via plane over a six-month period. The Baltimore Police Department put the Aerial Investigation Research, or AIR, pilot program into use in May 2020. It used a small airplane equipped with a high-resolution camera array to fly over the city for 40 hours per week during daylight in fair weather. The program was challenged under the First and Fourth Amendments by the ACLU of Maryland, but a federal judge denied the group’s request for an injunction halting it. While the rest of the case plays out, the ACLU appealed the injunction denial and went before a similarly unsympathetic three-member Fourth Circuit panel in September.