For which planes do Federal Aviation Administration (FAA) regulations apply? Do they apply to all planes entering the United States and all planes departing the United States? Do they also apply to planes registered in the United States but flying between airports outside the United States?
In a comment, you say that you're interested in the FAA regulation cited by the TSA in its page on airline passengers carrying lithium batteries in their luggage. That regulation is 49 CFR 175.10(a)(18). It basically applies to any aircraft flying to, from, or within the US, and all aircraft registered in the US, with some exceptions noted below, and perhaps some other exceptions that I have not identified.
The scope of the regulation is given in 49 CFR 175.1, which defines "Purpose, scope and applicability" for all of 49 CFR 175:
§ 175.1 Purpose, scope and applicability.
(a) This part prescribes requirements that apply to the transportation of hazardous materials in commerce aboard (including attached to or suspended from) aircraft. The requirements in this part are in addition to other requirements contained in parts 171, 172, 173, 178, and 180 of this subchapter.
(b) This part applies to the offering, acceptance, and transportation of hazardous materials in commerce by aircraft to, from, or within the United States, and to any aircraft of United States registry anywhere in air commerce. This subchapter applies to any person who performs, attempts to perform, or is required to perform any function subject to this subchapter, including -
(1) Air carriers, indirect air carriers, and freight forwarders and their flight and non-flight employees, agents, subsidiary and contract personnel (including cargo, passenger and baggage acceptance, handling, loading and unloading personnel); and
(2) Air passengers that carry any hazardous material on their person or in their carry-on or checked baggage.
(c) This part does not apply to aircraft of United States registry under lease to and operated by foreign nationals outside the United States if:
(1) Hazardous materials forbidden aboard aircraft by § 172.101 of this subchapter are not carried on the aircraft; and
(2) Other hazardous materials are carried in accordance with the regulations of the State (nation) of the aircraft operator.
(d) The requirements of this subchapter do not apply to transportation of hazardous material in support of dedicated air ambulance, firefighting, or search and rescue operations performed in compliance with the operator requirements under federal air regulations, title 14 of the CFR.
For reference, "commerce" is defined at 49 CFR 171.8 as
trade or transportation in the jurisdiction of the United States within a single state; between a place in a state and a place outside of the state; that affects trade or transportation between a place in a state and place outside of the state; or on a United States-registered aircraft.
Answer in a comment from phoog:
Different FAA regulations will apply to certain planes for different reasons. Some may apply because the plane is registered in the US. Others may apply because the plane is owned by a US carrier or by a foreign carrier approved to operate in the US. Others may apply because the plane is built in the US. Others may apply because the plane is flying through US airspace.