Part 91

Small non-commercial aircraft within the United States

Part 121

Large U.S.-based airlines, regional air carriers, and all cargo operators

Part 135

Small single aircraft operators to large operators that often provide a network to move cargo to larger Part 121 air carriers

Part 141

Federal Aviation Administration (FAA)-certificated pilot schools

Part 145

Maintenance facilities that are engaged in the maintenance, inspection, and alteration of aircraft and aircraft products

OEM

Original Equipment Manufacturer