Civilian airplanes have different maintenance programs depending on type and usage. Single engine private airplanes like a Cessna 172 may require simple service/inspections every 50 or 100 hours of flight, and one major "Annual" inspection during the calendar year, while large commercial aircraft are usually maintained under a "progressive" inspection program, where specific "A" and "B" checks are conducted on a daily and weekly schedule to insure the complete airplane and its components are inspected over the course of a designated time period. "C" and "D" Checks are considered to be "heavy maintenance" inspections, and are conducted after several thousands of flight hours. They involve removing, inspecting and repairing major components of the aircraft, including engines, control surfaces, landing gears and sometimes even removing the wings from the fuselage. These heavy checks on large commercial airplanes can keep dozens of trained and certified mechanics and inspectors busy for several weeks of 24-hour per day tear-down and inspection.
I'm a licensed aircraft mechanic (A&P)