Final answer:
If the HIAL system fails, the amendment required would be to increase the minimum visibility to compensate for the loss of visual guidance during approach and landing.
Step-by-step explanation:
In the context of aviation and instrument flight rules (IFR) operations, HIAL (High Intensity Approach Lighting) systems provide critical visual cues necessary for a pilot to align the aircraft with the runway for landing during periods of low visibility. Should HIAL fail and become inoperative, pilots would require a greater visual reference to compensate for the loss of these lights.
Therefore, the necessary amendment in response to HIAL failure would be to increase the minimum visibility requirements for the approach. This is a safety precaution to ensure that the pilot has sufficient visual reference to complete the approach and landing without the enhanced visual guidance that HIAL provides.