Which of the following is NOT an electrical failure type indicated?

The correct choice indicates that "Ghost circuit" is not a recognized type of electrical failure in the context of MTA tower operations.

AC power failure, DC power failure, and GRD (ground) failure are all well-defined issues that can occur in electrical systems. AC and DC power failures refer to interruptions in their respective power supplies, which can affect the functioning of various systems on the tower. GRD failure relates to issues with the grounding system, which is vital for safety and system stability, as it ensures that electrical faults are safely dissipated.

In contrast, a "Ghost circuit" typically refers to a misleading or phantom circuit condition that may not necessarily indicate a true electrical failure but can cause confusion or misinterpretation in troubleshooting. As it does not represent a clearcut failure type in electrical systems according to standard practices, it is the correct choice for this question.