In the realm of Air Traffic Control (ATC) within the United States, there is no single "hard" number written as a universal minimum in all phases of flight, but there is a standard expectation defined in the Aeronautical Information Manual (AIM). When an pilot is given a climb or descent clearance, ATC expects the aircraft to maintain an optimum rate of at least 500 feet per minute (fpm) until reaching the assigned altitude. If a pilot is unable to maintain at least 500 fpm, they are required to inform ATC. In 2026, with increasingly congested airspace and precision-based navigation, maintaining this rate is crucial for "sequencing" and ensuring separation between aircraft. During the final stages of an approach, the descent rate is governed by the glide slope (typically around 700-800 fpm for a 3-degree path), but for general en-route transitions, 500 fpm remains the "floor" for standard operations unless otherwise coordinated for safety or performance reasons.