Dead air
Dead air is an unintended period of silence that interrupts a broadcast during which no audio or video program material is transmitted. Radio and television. Dead air occurs in radio broadcasting when no audio program is transmitted for an extended period of time, usually more than a few seconds. In television broadcasting, the term denotes the absence of both audio and video program material. Technically, a carrier wave is still transmitting. In radio, the result is silence, and in television, the result is a silent black or gray screen. Television directors may use the command "fade to black  or to black" to indicate a momentary transition to a completely black image. However, the term "dead air" is most often used in cases where program material comes to an unexpected halt, either through operator error or technical malfunction. Among professional broadcasters, dead air is considered one of the worst things that can occur. Moreover, dead air may impact advertising revenue if it affects the airplay of paid commercials. The term "dead air" does not refer to a broadcast transmitter that is intentionally shut down, i.e. "closed", "signed off" or "off the air", by a control operator. Such a broadcast  transmitter is said to have gone "dark". Broadcast regulations. In the U.S., dead air, if prolonged and occurring without permission, is an actionable offense that can result in fines from the Federal Communications Commission (FCC). Broadcast stations can use programmable devices known as "silence sensors", "off air alarms" or "silence monitors" that will sound an alarm and alert personnel if dead air persists more than a few seconds. Examples. On September 11, 1987, Dan Rather walked off the set of the "CBS Evening News" when a late running U.S. Open tennis match threatened to delay the start of his news  broadcast. The match then ended sooner than expected but Rather was gone. The network broadcast six minutes of dead air before Rather was found and returned to the studio. CBS affiliates criticized Rather for the incident. One significant case of dead air occurred during Super Bowl LII in 2018, when the NBC television broadcast experienced 26 seconds of dead air during a commercial break. The network blamed "a brief equipment failure." NBC reported that no commercial advertising was lost. Prior to Super Bowl XLV, Green Bay, Wisconsin, radio station WCHK-FM announced that it would intentionally go to dead air  during the game, since the hometown Packers were playing in the game and station management believed nobody would be listening to music while the Super Bowl was being broadcast on another station. Prevention. Many broadcasters install a silence detector independently operating from their broadcasting headquarters. In the event of dead air lasting more than an acceptable duration, e. g. ≤ −70 dB and (if applicable) static/no picture for 30 seconds, an emergency program is cued. The emergency program contains at least some generic audio (and video) with a station identification. Radio stations usually play a loop of music. The  playlist is fixed so staff listening in to their own station can recognize the pattern of titles, infer how long the outage has already (at least) lasted and take action to fix the problem. Apart from providing a safeguard in the event of "unscheduled" interruption (like a fire in the building or technical issues), this mechanism may be used "deliberately" during programmed blackouts caused by strikes of technicians, journalists, and producers. When staff of the French public broadcasting network Radio France went on strike in September 2020, a pretaped message informing listeners that no service is available due to industrial  action was inserted into the loop.