If tachometer failure occurs, which gauge should be trusted?

When a tachometer failure occurs, it's essential to rely on additional systems and instruments to maintain safe operation of the helicopter. The governor, which automatically adjusts the throttle to maintain rotor RPM, alongside other flight instruments, provides critical information about the helicopter's performance.

The governor's functionality is designed to ensure that the rotor speed stays within safe operational limits, making it a reliable source of information when the tachometer is not providing accurate readings. Other gauges, such as the engine RPM indicators or performance instruments, can also provide essential insights into the helicopter's status and help the pilot maintain control and safety.

Relying solely on the RPM gauge, fuel gauges, or visual estimation for altitude does not take into account the collective understanding needed to manage the helicopter effectively in the absence of a tachometer reading. These alternative options do not offer comprehensive information about the helicopter’s rotor system and overall performance, which is vital for safe flight operations in such circumstances.