14 CFR § 91.525

No pilot in command may permit cargo to be carried in any airplane unless—

It is carried in an approved cargo rack, bin, or compartment installed in the airplane;

It is secured by means approved by the Administrator; or

It is carried in accordance with each of the following:

It is properly secured by a safety belt or other tiedown having enough strength to eliminate the possibility of shifting under all normally anticipated flight and ground conditions.

It is packaged or covered to avoid possible injury to passengers.

It does not impose any load on seats or on the floor structure that exceeds the load limitation for those components.

It is not located in a position that restricts the access to or use of any required emergency or regular exit, or the use of the aisle between the crew and the passenger compartment.

It is not carried directly above seated passengers.

When cargo is carried in cargo compartments that are designed to require the physical entry of a crewmember to extinguish any fire that may occur during flight, the cargo must be loaded so as to allow a crewmember to effectively reach all parts of the compartment with the contents of a hand fire extinguisher.