An aircraft reports established on an ILS localizer 10 NM from the runway. The localizer frequency is 109.9 MHz. What is the standard audio identification format transmitted by an ILS localizer?

1. A 2-letter or 3-letter Morse code identifier transmitted on the localizer frequency
2. A continuous voice broadcast of runway number
3. A high-pitched 1000 Hz continuous tone without Morse code
4. No audio signal is transmitted