Part 73, Subpart G, Section 73.845 is a regulation that addresses situations where the transmitter is out of compliance. It is also known as the "3-hour rule".
The 3-hour rule
This rule simply states that if there is an issue with the transmitter or other part of an LPFM station's technical operation that is out of compliance with the rules, the station must be shut down within three hours of the out of compliance condition. Many modern transmitters are equipped with fail safes that are able to detect some out of compliance conditions and automatically shut down.
This is why it is extremely important that someone has the ability to control the transmitter at any time, especially if the transmitter is not at the same site as the studio. This means some form of remote control. Many modern certified transmitters have web interfaces to the transmitter that allows many functions to be monitored and controlled just by using a web browser.
If the station does have to shut down, the station's log must be updated to include the date and time that the out of compliance condition was noticed, the issue that is taking place and the time when the transmitter was shut down as well as the name of the person who made the entry into the log.
This is also why it is important for LPFM stations to only use a certified transmitter that has an FCC ID label affixed to it.
Regulatory history
This rule was enacted in the original 2000 LPFM Report and Order and has not been amended since.
Text of regulation 47 CFR §73.845
§ 73.845 Transmission system operation.
Each LPFM licensee is responsible for maintaining and operating its broadcast station in a manner that complies with the technical rules set forth elsewhere in this part and in accordance with the terms of the station authorization. In the event that an LPFM station is operating in a manner that is not in compliance with the technical rules set forth elsewhere in this part or the terms of the station authorization, broadcast operation must be terminated within three hours.