Yes. It is interesting that the Big Boeing Book, in one place, says the descent path is cut to half the idle descent path, but also indicates that the same logic is used for a cruise descent.
Cruise descent is used for enroute cruise altitude change, NOT in the descent phase of flight.
- A cruise descent can be started on the MCP by selecting a lower altitude and pushing the altitude
selector. If you do not have altitude intervention, enter the lower cruise altitude in 1L of the CDU pg.
- In a CRZ DES, the cruise descent guidance law is applied.
It initially uses a predicted thrust which will result in approximately 1,200 ft per minute descent and
at the cruise descent airspeed. When VNAV estimates that the thrust target has been achieved for this
descent rate, throttle clutches disengage (dormant) and FMA annunciates THR HOLD just as in a DES NOW function.
- Once the autothrottle is set to the HOLD mode, the pilot can position the throttles to control desired
vertical speed; a very nice design.
- If a CRZ DES intercepts the planned descent profile, the descent path is captured and DES becomes
active. This is NOT what the CRZ DES feature was designed for.
The cruise descent guidance law - IDLE to 1200 fpm then
THR HLD - is used in the following situations:
1 When descending from one cruise altitude to another.
2 When making an early descent before the end of cruise.
3 When engaging VNAV when below the descent path.
4 When the airplane is flying a descent path and, after a
modification, ends up below the reconstructed descent
path