What signifies a loss of radar heartbeat in the TOMS system?

The correct answer signifies a loss of radar heartbeat in the TOMS (Tactical Operational Mission System) is if the SPDS (Smart Platform Data System) is in failsafe mode. When the SPDS enters failsafe mode, it indicates that the system has detected an issue with the radar's operational status, leading to a loss of the regular communication or "heartbeat" signal it sends to confirm that it is functioning properly. This situation is critical as it points towards potential system failures or communication issues that require immediate attention.

In contrast, the other options do not directly imply a loss of radar heartbeat. Increased altitude, for instance, pertains more to flight operations rather than system status. Automatic landing mode is a specific operational state of the aircraft and does not relate to radar functionality, while engine failure notifications deal with propulsion issues rather than radar communications. Thus, understanding the relationship between SPDS and the radar heartbeat is vital for maintaining situational awareness and addressing system anomalies promptly.