• A Check:

Performed about every 500 to 800 flight hours or up to 400 cycles. It requires up to 100 man-hours to perform and it is typically carried out at an overnight stop.

• B Check:

Required every 4 to 6 months and requires about 150 man-hours and takes about I day.

• C Check

This check is comprehensive and the entire aircraft is inspected. It is conducted every 21 months and requires about 6,000 man hours.

• D Check

The D Check is the most expensive and demanding costing about $7 million and requiring up to 100,000 man hours depending upon the age of the aircraft. These are completed about every five years and airlines must plan well in advance to ensure that it does not have too many aircraft requiring D Checks at the same time.