When does the amber HYDR FL LO annunciator illuminate?

The amber HYDR FL LO annunciator illuminates when the hydraulic reservoir fluid level drops below approximately 1 quart. This illuminates as a warning to pilots that the hydraulic system may be experiencing a low fluid condition, which could lead to inadequate hydraulic pressure for operating systems dependent on hydraulic power. Monitoring fluid levels is critical for maintaining system integrity and ensuring safe operation of the aircraft, as insufficient hydraulic fluid can impair control surfaces and other hydraulic-dependent components.

The other options involve different conditions not related to fluid level. For instance, the state of being overfilled would not trigger this specific warning; excessive hydraulic pressure and temperature extremes pertain to different system indicators and wouldn’t affect fluid level warnings. Understanding this specific threshold is essential for effective pre-flight checks and in-flight monitoring of aircraft systems.