The FAA issues a letter authorizing a pilot to be a Check Airman for an Air Carrier. There are three main boxes the FAA can tick. You can be a LCA, you perform PIC's yearly line checks looking for standardization. You would also give new hires and upgrading pilots Operating Experience (OE). You're a babysitter while the pilot starts applying what they learned in the schoolhouse to the real world. And the airline may have a proceedure for special airports where a Captain has to operate into the airport with a LCA before they can fly in on their own.
The other main boxes are Check Airman simulator and Check Airman airplane. They are futher broken down to what checks can be given and from which seats.
Last edited by MarkerInbound; 26th Jul 2013 at 13:59.