3C check: Some authorities use a 3C check, also known as Intermediate Layover (IL). This type of check includes light structural maintenance, including inspection or checks for corrosion or high-load parts of the aircraft. The 3C check may also be used as the opportunity for aircraft upgrades such as the installation of new carpets etc.
D Check: The D check, also known as a 'heavy maintenance visit', is the most extensive and demanding check for an airplane. This check is performed every 6-10 years and requires the whole plane to be taken apart for thorough inspection and overhaul. The inspection generally takes up to 50,000 person-hours and two months to complete depending on the number of technicians involved. It can only be performed at a suitable maintenance base.
