What is an "altitude restriction" in the context of VNAV?

An altitude restriction in the context of VNAV refers to a limitation on the altitude that an aircraft must maintain at a specific waypoint. This is crucial for ensuring safe separation between aircraft, managing air traffic flow, and adhering to published procedures during flight. These restrictions are often depicted on charts and communicated in air traffic control instructions to maintain safe distances from terrain or other aircraft.

Maintaining specific altitudes at waypoints helps to organize traffic in busy airspace and ensures that aircraft are at the appropriate altitude for the route they are flying. This is especially important as aircraft approach or depart from busy airports, where altitude management can be critical for safety and efficiency.

The other options do not accurately reflect the concept of altitude restrictions within VNAV. For instance, setting a minimum speed limit at high altitude pertains more to aircraft performance than to altitude management specifically at waypoints. Similarly, maximum altitude during ascent and the altitude to begin descent are different aspects of flight planning and do not define the restriction applied at a particular waypoint.