What is the first indication of an alternator failure in an aircraft?

The first indication of an alternator failure in an aircraft is typically the illumination of the low voltage light. When the alternator is not functioning properly, it can no longer supply the necessary electrical power to the aircraft's systems, leading to a drop in voltage. The low voltage light serves as an alert to the pilot that the electrical system is not operating within its normal parameters, indicating a potential failure of the alternator or issues related to the electrical supply.

This warning is crucial as it allows the pilot to take immediate action. Recognizing the low voltage condition early enables the pilot to manage resources effectively, assess the situation, and consider landing as soon as conditions permit. Other system warnings, like low oil pressure, high temperature gauges, or fuel pressure drops, do not directly indicate alternator performance but rather relate to their respective systems, which could potentially be affected by an electrical failure but are not the initial signals of an alternator issue.