Common carriers are required to exercise the highest degree of care in safety:

49 U.S. Code § 44701 - General requirements

(d)Considerations and Classification of Regulations and Standards.—When prescribing a regulation or standard under subsection (a) or (b) of this section or any of sections 44702–44716 of this title, the Administrator shall—

(1)consider—

(A)

the duty of an air carrier to provide service with the highest possible degree of safety in the public interest;

From Wikipedia: A common carrier is distinguished from a contract carrier (also called a public carrier in UK English), which is a carrier that transports goods for only a certain number of clients and that can refuse to transport goods for anyone else, and from a private carrier. A common carrier holds itself out to provide service to the general public without discrimination (to meet the needs of the regulator's quasi judicial role of impartiality toward the public's interest) for the "public convenience and necessity." A common carrier must further demonstrate to the regulator that it is "fit, willing, and able" to provide those services for which it is granted authority. Common carriers typically transport persons or goods according to defined and published routes, time schedules, and rate tables upon the approval of regulators. Public airlines, railroads, bus lines, taxicab companies, phone companies, internet service providers, cruise ships, motor carriers (i.e., canal operating companies, trucking companies), and other freight companies generally operate as common carriers. Under US law, an ocean freight forwarder cannot act as a common carrier.