What type of signal does an ELT emit after activation?

The emergency locator transmitter (ELT) emits a continuous audio tone after activation, which is specifically designed to facilitate search and rescue operations. This audio signal broadcasts on distress frequencies, allowing search and rescue teams, as well as aircraft monitoring the frequency, to identify the location of the emergency situation. The continuous nature of the signal helps to ensure that it can be easily detected over a wide area, making it critical for locating an aircraft in distress.

In contrast, the other options do not accurately describe the function of an ELT. A distress visual signal typically refers to visual signals used in emergency situations, not audio. Radio silence is a state of no communication, which would hinder the search and rescue efforts instead of aiding them. A coded message would imply the use of specific codes to convey information, which is not how ELTs operate; they simply emit a continuous signal to indicate an emergency.