There are 3 pitch controlled decent modes: level change (MCP), path and speed descent (FMC). All methods use pitch control to slave the A/C to either airspeed, flight path or target speed, respectively. The path and speed descent modes allow for manual or ECON target speed settings, for which ECON speed is a function of the cost index (standard setting of 40 for VNAV climb optimizing). As I understand it, with
Path descent mode,
1 – target speed is set (ECON or manual)
2 – manual pitch is set (via spoileron and thrust levers) to control the path speed
3 – pitch auto-controlled (via AFDS) to slave the A/C to the flight path (FPA) at the T/D
4 – target speed maintained at E/D
Speed descent and level change mode,
1 – target speed is set (ECON or manual)
2 – manual pitch is set (via spoileron and thrust levers) to control the flight path
3 – pitch auto-controlled (via AFDS) to slave the A/C to the target speed at the T/D
4 – target speed maintained at E/D
Hence, thrust and spoileron are optional for pitch control in descent mode!
Regards,
Stephen Wood
PS you should also use pitch control (thrust and spoilerons) to keep your A/C on its G/S path during ILS approaches!
[ 25 November 2001: Message edited by: Stephen Wood ]