It is illegal in most countries to transmit on the airband frequencies without a suitable license, although an individual license may not be required, for instance in the US where aircraft stations are "licensed by rule".[19] Many countries' regulations also restrict communications in the airband. For instance, in Canada, airband communications are limited to those required for "the safety and navigation of an aircraft; the general operation of the aircraft; and the exchange of messages on behalf of the public. In addition, a person may operate radio apparatus only to transmit a non-superfluous signal or a signal containing non-profane or non-obscene radiocommunications."[2]