Most US Government agencies employ the services of internal or external auditors to ensure that aircraft and pilots contracted from commercial operators meet the requirements in terms of equipment fit and pilot experience specified in the contract. This makes sure that the Government Agency gets what they are paying for and that lesser capable equiopment and or personnel are not substituted for expediency. It also ensures that the Government Agency has discharged its duty of care by not only specifying but auditing against their standards.
Pilots and aircraft employed on the NSF Antarctica contract for example have to be cahecked against the contract specifications prior to each season.
Once checked and found to be compliant, a card or approval is issued against the individual aircraft and or pilot. This is known as "carding". Aircraft and pilots are then considered to be "carded" which entitles them to carry out the required operations.