KLM MD-11 - Guidance

MD-11 Flight Crew Operations Manual
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FMS -
Description and Operation
FMS.10.6
Guidance
The FMS guidance function provides commands for controlling aircraft roll,
pitch, speed and engine thrust. Fully automatic, performance-optimized guidance
along flight paths in two or three dimensions is available. This is accomplished
using SPD/NAV/PROF modes of the FMS coupled via the FCP. SPD, NAV and
PROF may be used separately or together. NAV provides lateral guidance and
speed/thrust control.
Lateral Guidance - This is provided by a primary flight plan with automatic route
leg sequencing. The NAV guidance function compares the aircraft actual position
with the desired flight path and generates steering commands to the autopilot and
flight director. This causes the aircraft to fly along the desired path. Direct
guidance from the aircraft present position to any waypoint is also available.
Vertical Guidance - This encompasses the takeoff, climb, cruise, descent, and
approach phases of the flight plan. The flight planning capability of the FMS
includes means to enter published departure, arrival, and approach segments and
individual waypoints that include speed/altitude and time constraints. These
constraints, as well as the entered cruise altitude and cost index define the vertical
profile for which FMS provides guidance.
In the climb portion of the profile, the Autoflight System (AFS) will control thrust
from FMC thrust limits and speed targets via the FCCs. The aircraft will climb at
climb limit thrust to each altitude constraint, fly level until past the constraining
waypoint using an appropriate speed target, and then resume the climb at CLIMB
LIMIT thrust. Automatic level-off will also occur as a function of the altitude
setting on the FCP.
The climb speed schedule is a function of the speed limit and speed constraints at
lateral waypoints. If not restricted by either of these conditions, the selected
performance mode speed is used. After reaching the cruise altitude, the SPD mode
will maintain the selected performance mode speed until the descent phase is
reached.
The descent path generator calculates a vertical path that meets waypoint
altitude/speed constraints. This calculation also considers the selected DES
performance mode. The path construction to the first altitude constraint assumes
idle thrust and a calculated descent gradient which will maintain the mode speed
schedule or the limit speed under the predicted wind conditions. PROF guidance
controls aircraft pitch in a manner similar to the tracking of an ILS beam. While
flying the descent path, PROF pitch commands to the FCC hold the path while the
pilot uses speed brakes to maintain speed if a significant, unanticipated
acceleration occurs. The FMS mode in descent on the FMS path will be a
speed-on-throttle mode. Slight throttle activity may occur in an FMS descent to
maintain the SPD target.
October 02, 2006