According to AFMAN 11-217 Vol 1, when can an aircraft begin a descent to the next lower altitude?

The appropriate time for an aircraft to begin a descent to the next lower altitude is based on operational procedures as specified in regulations. In this case, selecting the pre-calculated lead turn point is essential as it aligns with navigation planning and safety protocols. The lead turn point is strategically determined to ensure that descent begins at the correct phase of flight for optimal performance and efficient navigation.

This timing allows pilots to begin a descent while considering aircraft performance factors, maintaining safe altitudes during turns, and preparing for an approach. Ensuring the descent starts at this calculated point helps avoid obstacles and complies with airspace restrictions, contributing to overall flight safety.

In contrast, descending upon reaching a cloud could lead to visibility and safety issues if not appropriately planned. Waiting for a clearance from Air Traffic Control, while critical when indicated, does not specifically relate to a predefined procedural point in descent planning. Beginning a descent only after reaching cruise altitude does not reflect an accurate understanding of when to transition to a lower altitude during operational maneuvers.