Which vertical mode meets FMGC altitude constraints?

The mode that meets FMGC altitude constraints is CLB (Climb Mode). In this mode, the Flight Management and Guidance Computer (FMGC) actively manages the aircraft's climb performance by taking into account various parameters, such as airspeed, engine thrust, and the aircraft's current altitude. This ensures that the aircraft adheres to predefined altitude constraints during the climb phase of flight.

When the CLB mode is engaged, the FMGC provides the necessary guidance to achieve the specified climb rate and will also manage step climbs according to the altitude constraints programmed into the flight management system. This capability is critical for maintaining air traffic control clearances and ensuring safe altitude separations with other traffic.

In contrast, the other modes such as OP CLB (Optimized Climb) and EXP CLB (Expedited Climb) do not necessarily adhere to the same constraints as standard CLB mode. They may prioritize different operational objectives, which could result in deviations from altitude constraints. V/S (Vertical Speed) mode manually controls vertical speed and does not provide the same level of management for altitude restrictions compared to the standard CLB mode. Therefore, CLB mode is the most reliable choice for meeting FMGC altitude constraints during a climb.