(2)
Temperature predictions use the present temperature, and a manually entered value for Top-Of-Climb (TOC) temperature. The FMC linearly interpolates between the temperature values, similar to the wind prediction.
D. Speed and Thrust Targets and Thrust Limits
(1)
In terms of fuel consumed per nautical ground mile traveled, the variable mach speed schedule offers an improvement over the conventional constant mach schedule. Variable mach is dependent upon cost index, airplane gross weight, and pressure altitude.
(2)
For any value of cost index chosen by the operator, the FMCS continuously computes and updates economy cruise speed in flight, as a function of a parameter known as cost factor. The FMCS evaluates this function continuously in the cruise flight phase to find the speed at which the minimum cost factor occurs. This is the most economical cruising speed.
NOTE: Cost index relates the direct hourly flying costs to
____ the cost of fuel. Cost factor is approximately equal to cost index divided by true airspeed.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
(3)
The economy climb and descent speed schedules have been derived from aerodynamic data, to provide minimum trip cost based on cost index and airplane gross weight.
(4)
Other speed schedules are the normal maximum rate and maximum angle climb, and long range cruise schedules. Manually entered speeds can be used, if current flight conditions allow.
(5)
The FMCS provides speed and thrust targets for the selected flight phase and mode of operation. The FMCS also computes thrust limits to assure protection of the engines against possible overboost. The speed targets are transmitted to the DFCS, and displayed on the air data instruments. The thrust targets are transmitted to the A/T, and displayed on the engine instruments.
E. Flight Envelope Protection
(1) Speed and thrust targets provided by the FMCS must not exceed the limits of airplane and engine performance. Also the systems flight planning computations must offer performance options that are within the airplanes capabilities. The FMCS operational program continuously monitors actual flight conditions, computed performance targets, and data entries. These variables are evaluated by the FMCS with respect to the computed or programmed capabilities of the airplane and its engines. Any condition that exceeds the airplane or engine performance limits is flagged as invalid, and the actual outputs of the system are restricted by the computed limit boundaries.
F. Performance Modification Factors
(1) The aerodynamic and engine models used as the performance data base for the FMCS represents the average, in-service model of the 737-300/-400/-500. This data is derived from airplane design information and flight tests. Since each airplane performance is different, factors which adjust the airplane drag and fuel flow modeling data over a range of -9.9% to +9.9% from the baseline may be entered on the CDU and are retained in NV RAM for continued use.
9. Navigation Computation______________________
A. The FMC has provisions for both self-contained and radio-augmented navigation. The system furnishes continuous solutions for the following basic navigational outputs. These basic outputs apply to navigation in the lateral and vertical planes.
(1) Airplane Position (latitude, longitude, and altitude)
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