*
VNAV path
*
Thrust (thr) targets
*
Thrust and speed limit commands to fly and guide the airplane along the vertical flight profile trajectory predictions
*
Fuel weight calculations
*
Quick reference handbook (QRH) calculations.
The FMCF VNAV sub-function also uses this data to calculate VNAV outputs:
*
Airframe sensors and components
*
Engine sensors and components
*
Flight deck control panels
*
Flight deck switches.
The VNAV sub-function responds to BITE requests and supplies display data to the display control sub-function.
Speed/Mach, Path, and Thrust Targets
The VNAV sub-function calculates the optimum speed/mach, path and thrust targets. These calculations occur during climb, cruise, and the descent flight phases with an active lateral route and vertical flight plan.
The speed/mach targets go to the guidance sub-function. The guidance sub-function supplies steering commands to the autopilot flight director system (AFDS). SPD on elevators use SPD/MACH targets in climb. Path on elevators use altitude (path) targets in cruise and descent to control the pitch axis of the airplane.
The thrust management computing function uses target speed on throttles or target thrust on throttles. It uses speed/MACH targets or thrust targets to control the thrust of the airplane. The TMCS uses thrust targets in climb and descent and speed/ MACH targets in cruise to control the thrust of the airplane.
Trajectory Predictions
The trajectory section uses these to simulate the airplane trajectory over a flight plan:
*
Equations of motion
*
Models of the airplane
*
Engine characteristics.
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The trajectory calculation optimizes the time the airplane is in an idle engine thrust configuration. The calculations do not violate speed and altitude restrictions.
The flight plan prediction section calculates the flight trajectory from takeoff to landing. To do this, it uses internal data and these inputs:
*
VNAV performance page data (GW, cost index, ALT, fuel quantity, reserve fuel)
*
Active route with end of descent point
*
Present position
*
Wind at altitude
*
Icing conditions forecasts
*
Performance factors (Fuel flow, climb thrust derate, and drag).
These outputs go to the display control sub-function to show on the CDU and the primary display system. The cabin pressure system receives this data to calculate the cabin pressurization schedule in climb, cruise and the descent flight phase.
Thrust/Speed Limit Protection
The target thrust section of the VNAV sub-function calculates a maximum and a minimum thrust limit and speed limit for climb, cruise, and the descent flight phases. To do this, the VNAV sub-function uses this data:
*
Engine and airframe database
*
Models of the airplane
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ADIRU data (altitude, temperature and barometric pressure)
*
Gross weight
*
Airplane configuration.
The AFDS (speed) outputs do not exceed the VNAV sub-function speed limits in automatic flight control when the VNAV mode is active. The autothrottle speed or thrust outputs do not exceed the VNAV sub-function speed or thrust limits when VNAV is active.
Fuel/Weight Calculation
The fuel/weight section calculates fuel burn-off, fuel remaining, and airplane gross weight. It also sends a fuel quantity alert message when the fuel quantity system and fuel calculation differs by 9,000 pounds.
Quick Reference Handbook Calculations (QRH)
The QRH section calculates these advisory takeoff speeds:
*
V1
*
VR
*
VREF
*
V2
*
CG
*
Takeoff stabilizer position equal to those found in a QRH.
The data for this section comes from the performance data base (PDB).
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The advisory stabilizer position calculation needs a gross weight and CG entry.
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