What is the primary function of the ammeter in an aircraft electrical system?

The primary function of the ammeter in an aircraft electrical system is to indicate charge or discharge in the battery. This instrument measures the flow of electrical current, allowing pilots to monitor the performance of the electrical system in real-time. When the ammeter shows a positive current, it indicates that the battery is being charged by the alternator or generator. Conversely, a negative reading signifies that the battery is discharging, meaning the electrical demand on the system exceeds what is being generated. Keeping a close eye on the ammeter is crucial for ensuring that the battery remains adequately charged during flight and that the electrical system is functioning properly.

In contrast, other functions mentioned in the options—such as providing altitude information, showing aircraft speed, or measuring fuel flow—are carried out by other instruments in the cockpit specifically designed for those purposes, making the ammeter's role unique and vital for monitoring the health of the aircraft's electrical system.