Final answer:
Time-critical updates about airports and the national airspace are given through Notices to Airmen (NOTAMs), which are vital for pilots to obtain current information about airport conditions and restrictions.
Step-by-step explanation:
Time-critical information on airports and changes that affect the national airspace system are provided by Notices to Airmen (NOTAMs). NOTAMs are essential for the aviation community, offering updates on factors such as temporary airspace restrictions, airport or runway closures, and other critical data. The other options listed, The Chart Supplement U.S. and Advisory Circulars (ACs), also serve important roles in aviation. The Chart Supplement provides detailed information of airports, heliports, and seaplane bases. Advisory Circulars convey the Federal Aviation Administration's (FAA) recommendations on aviation matters, but are not as time-sensitive as NOTAMs.