Passenger transport and business aircraft are fitted with a range of cabin systems and equipment for passenger safety, convenience and entertainment. Typical applications for this equipment include lighting, audio and visual systems. Cabin lighting is used for the safety and comfort of passengers; this was described in Chapter 12. Audio systems include the passenger address system used by the flight or cabin crew to give out safety announcements and other flight information. These announcements are made from hand-held microphones and are heard over loudspeakers in the cabin and passenger headsets. The same system can be used to play automatic sound tracks; this is often used for announcements in foreign languages, or to play background music during boarding and disembarkation. Audio systems are also available at the individual seat positions.