Definition

Preselected altitude is the value entered into the altitude selector window of a pilot's Primary Flight Display (PFD). This is normally on the right side of the PFD, above the altitude display tape.

Description

When Air Traffic Control (ATC) gives an aircraft a new altitude, the Pilot Flying (PF) will enter that altitude into the altitude selector. The PF will then select a climb or descent mode, i.e., vertical speed, flight path angle, etc. This altitude is usually entered manually with a selector knob on the guidance panel. The aircraft will climb or descend until it captures the selected altitude.

When Mode S enhanced surveillance is in use, air traffic controllers can see this selected altitude on their screens. This provides a safety net to prevent altitude deviations. For example, if ATC clears an aircraft to climb to FL260 but the controller sees FL360 as the selected altitude, that presents an opportunity for the controller to prevent an error.

When flying a Standard Arrival Route (STAR), a flight crew might receive an ATC clearance to "descend via" that route. In that case, the PF will enter in the altitude selector the lowest altitude on the arrival route. With typical flight management systems that include vertical navigation functions, the aircraft will descend via the STAR, respecting all intermediate altitudes along the route until reaching the bottom altitude.