MD-11 Flight Crew Operations Manual
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FMS -
Description and Operation
FMS.10.5
MAX CLB - The MAX CLB speed is a table look-up speed for best angle of
climb.
MAX END - The MAX END and best holding speed targets are calculated for
obtaining the least drag for maximum time aloft.
MAX DES - The MAX DES speed is based on operation at maximum flight
speeds.
The performance functions include the computation of optimal speeds, estimates
of fuel consumption, and gross weight, predictions of time, fuel, and distances, at
all flight plan waypoints. It also covers the computations of reference parameters,
such as optimum altitude, maximum altitude, approach speed, database
search/retrieval and FMC calculation of the operational speed envelope.
Flight path predictions are computed by the FMC using an origin to destination
trajectory that is based on gross weight, cost index, predicted cruise winds,
speed/altitude/time constraints at specific waypoints, and specified modes for
climb, cruise, descent, and approach. Allowances are made for takeoff and
acceleration requirements between the legs of the vertical profile. The predictions
are updated periodically as the flight progresses incorporating Aircraft (A/C)
performance and Ground Speed (GS).
Descent path synthesis predicts the descent path by assuming flight idle thrust
above the descent speed limit altitude and a small adjustment above idle below
this altitude. The synthesis starts at the destination to compute the point where
slats/flaps are expected to be extended and then intersect the cruise altitude
creating a T/D point. This results in a predicted path that takes into account speed
targets, waypoint altitude constraints, and the impact of wind forecasts.
The optimum Step Climb (S/C) computes the best point along the route to initiate
a S/C to a pilot defined altitude that will result in minimum trip cost. The step-to
altitude is preselected by the pilot on the FCP. The system will then begin climb
at the programmed S/C point.
Approach speed targets are computed as a function of calculated gross weight and
slat/flap settings. The final approach speed (VAPP) contains a + 5 knot bias above
1.3 x VSO or VREF. This bias can be increased by pilot input for wind conditions.
The FMS fuel/weight/CG calculation is a prerequisite for all performance
computations.
After engine start, the fuel/weight calculation is updated on the basis of fuel tank
readings and a time integration of the fuel flows to each engine.
The route of flight is displayed on the Electronic Instrument System (EIS) map
display, and when the descent phase is active, a vertical deviation indicator is
displayed to show aircraft deviation from the computed flight path. Additionally,
appropriate PROF flight mode annunciation is displayed on the FMA (top of PFD)
to indicate whether the aircraft is tracking the descent vertical path.
October 02, 2006
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