The descent phase starts at the top of descent point and continues to the end of descent point. Planning for the descent phase starts during cruise.
The approach phase starts at the end of descent point and continues to touchdown or go-around. When a go-around is accomplished, the FMC enters a modified cruise or approach phase, depending on the route and cruise conditions.
PEGASUS FMC
Alternates can be selected at any time. Alternates are available from preflight through all phases of flight and can be updated at any time. Diversion to an alternate can be accomplished during cruise, descent, or approach.
The only automatic page change in the descent/approach phases is the VNAV selected page change, from cruise to descent, at the top of descent.
Early descent is commenced before reaching the top of descent. The description of early descent options and functions is in Section 42, FMC Cruise.
During descent, LNAV progress is managed using the RTE LEGS page, as in the cruise phase. VNAV descent management is accomplished primarily on the DES page.
Other pages which support descent are: