How many seconds should the Horizontal Stab anti-ice failure light be out during the test?

The correct response indicates that the Horizontal Stabilizer anti-ice failure light should be out for 3 seconds during the test. This specific timing is essential for pilots to ensure that the anti-ice system is functioning properly before takeoff or during critical phases of flight.

The duration is designed to provide a clear and adequate interval for the crew to confirm that there are no immediate operational issues with the anti-ice system. If the light remains illuminated beyond this time frame, it may signal a malfunction or failure in the system that could potentially impact the aircraft's performance under certain conditions.

Familiarity with these operational checks and their timing is critical for effective aircraft operation and safe management of in-flight ice conditions. Understanding why 3 seconds is the benchmark allows pilots to recognize that the system's functionality is verified within a reasonable timeframe before proceeding with flight operations.