What signal indicates that a VOR is being tested using T-E-S-T code?

The correct answer highlights that a VOR (VHF Omni-directional Range) undergoing testing emits a specific coded Morse signal known as the T-E-S-T code. This code is crucial for pilots to understand whether the VOR is operational when they encounter it. The T-E-S-T code informs users that the VOR is not a typical navigational signal but instead indicates that testing is taking place.

Recognizing the presence of this coded Morse signal helps to ensure that pilots do not rely on a potentially non-functional VOR for navigation, which could lead to inaccuracies and navigation errors. Understanding the function of this signal is essential for safe flight operations, particularly in instrument flight where reliance on equipment accuracy is critical.

The other options do not convey the specific testing nature of the VOR signal. For instance, a continuous signal may suggest normal operation, while a variable signal could indicate malfunctioning equipment. The absence of a signal may create confusion regarding the status of the navigational aid, making it imperative for pilots to correctly identify the T-E-S-T Morse code during such tests.