EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITHOUT EFIS ú
34-62-00
ú ú 03 Page 43 ú Feb 25/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
(7) Position Updating
(a) When the Kalman filter has made an acceptable estimate of the errors in the basic IRS present position; the lateral position data used for airplane navigation is updated. If significant error exists between the present and update position, the present position data (used for steering guidance) is slewed at a controlled rate to match the update position.
J. Magnetic Variation
(1) The FMC computes the current value of magnetic variation at the airplanes present position. This magnetic variation is based upon the known angle between true north and magnetic north, at the nearest VOR facility in the navigation data base.
K. Navigation Aid Cone of Silence
(1) Before computing airplane present position, the FMC determines if the airplanes estimated position is within the cone of silence of a tuned navigation aid. This is done for both manually and automatically tuned navigation aid stations. If the airplane is estimated to be within the cone of silence of a tuned navigation aid, the VOR bearing or DME range received from that station will not be used for navigation calculations.
10. Navigation Aid and Tuning Management (Fig. 12)____________________________________
A. The FMCS relies upon a combination of VHF NAV, DME, IRS, and DADC inputs to provide position, heading, and velocity information for an optimal navigation solution. Most of the sensors provide this information independently, without requiring the attention of either the crew or the FMCS. There are, however two types of sensors that require some form of external control; these are the airplane's VOR receivers and DME interrogators.
B. Tuning Commands from the FMC go to the VORs and DMEs by way of the DAA. The receiver/interrogator pairs may be operated in either of two basic modes: manual or automatic. A MODE selector switch is located on each of the VHF NAV control panels. If a MODE switch is in the MAN position, the frequency command for tuning the VOR/DME pair comes from the control panel and is the frequency manually selected by the crew. When the switch is in the AUTO position, the frequency command originates in the FMC. The FMC automatically generates tuning commands, as a function of the available navigation aid ground stations relative to the navigation position estimate and the airplane altitude, by the station selection processes in the FMC software program. When both VHF NAV control panels are in the MAN mode, the FMC will use its normal navigation mode hierarchy as long as navaid geometry and range criteria are met.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITHOUT EFIS ú
34-62-00
ú ú 03 Page 44 ú Feb 25/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITHOUT EFIS ú
34-62-00
ú ú 06 Page 45 ú Nov 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
