MANAGE DESCENT AS AN ENERGY AND GEOMETRY PROBLEM
A descent must dispose of height and speed within the route and clearance that remain. A shortcut removes useful distance, a tailwind changes progress across the ground, and a late speed restriction changes the available trade between descent and deceleration. Assess the next meaningful point in both height and speed rather than considering vertical deviation alone. A path can be geometrically close while the aircraft is carrying too much energy for the intended configuration. Conversely, a speed correction can consume distance needed to meet a later altitude restriction. [21, PDF pp. 141–146]
DES works with the computed managed profile. In normal automatic use, OP DES uses idle thrust and pitch guidance to control speed towards the selected altitude without observing managed altitude constraints. V/S commands a vertical rate and leaves the crew to monitor whether speed and thrust can support the chosen descent. Choose the mode for the actual objective. A high vertical-rate demand cannot guarantee both the intended path and a satisfactory speed when available energy or thrust does not permit them. Read FMA, altitude authority, speed trend and remaining route together. [116, PDF pp. 3–4,10–12] [21, PDF pp. 141–146]
The official V3 presentation describes a Thales decelerated approach containing a level segment before final approach. Interpret such a segment through the active mode, altitude target and computed profile. A temporary level-off may be part of the energy plan, but it also needs to be distinguished from capture of a clearance level or a different active mode. Reassess after vectors, direct routing or a changed arrival. The earlier descent prediction belonged to the earlier lateral path, so preserving the same FCU inputs does not preserve the same operational situation. [53, Chapter LNAV/VNAV] [21, PDF pp. 141–146]
Make speedbrake use deliberate and compatible with the applicable limitations and aircraft state. Observe what an intervention achieves before adding another. The useful outcome is a restored path to the next restriction and configuration point, not simply a reduced vertical-deviation indication. Review the time left for gear and high-lift changes, checks and cabin readiness. When the required approach condition cannot be achieved with an understood plan, request more distance or use the appropriate discontinuation option rather than attempting to rescue the descent through an accumulating sequence of large late inputs. [21, PDF pp. 141–158] [21, PDF pp. 197–200]
Use a controlled training comparison: fly the planned arrival, then repeat from a known state with a documented shortcut. Record route distance, altitude, speed, configuration and FMA before and after the change. Predict the direction of the required adjustment before intervening. If a computation issue occurs, preserve the active plan and build information rather than inserting arbitrary restrictions merely to obtain a display. The dated V3 known-issues record includes prediction and managed-speed investigations; it is evidence for a particular software snapshot, not an alternative energy-management technique. [21, PDF pp. 141–146] [83, Prediction and managed-speed investigations,24–25 October 2026]