Use or disclosure of the information on this page is subject to the restrictions on the title page of this document. B747-400 FMS PILOT’S GUIDE 4.4 POLAR OPERA OPERATION TION This section identifies operation unique to the polar region for the magnetic/true reference and for the IRS mode. 4.4.1 Magnetic/True Reference Selection of magnetic or true reference is normally selected by the HDG TRUE/NORM switch located above the upper EICAS display. However, the reference is automatically changed to true, independent of the position of the HDG TRUE/NORM switch, when the aircraft is operating in the region above N73° or below S60° latitude. Upon leaving this region, the heading reference is again determined by the position of the HDG TRUE/NORM switch. When operating in the true reference mode, bearing information entered by the pilot is assumed to be a true bearing reference. 4.4.2 Polar IRS Navigation This section describes FMC navigation using the IRS when entering or leaving the polar region. For the purpose of navigation, the FMC position is considered to be in the polar region if its latitude is greater than 84°, or if its latitude is greater than 83.5° after having been greater than 84°. When the computed aircraft position enters the region above N84°, or the region below S84°, each FMC downmodes from the triple-mix IRS position to a single IRS position. The “SPLIT IRS OPERATION” message is displayed to inform the pilot the FMC has changed from triple-mix to split IRS position updating. Each FMC selects the corresponding valid IRS. For the left FMC, the order of selection is left, center, and right. For the right FMC, the order is right, center, and left. The IRS selection may be checked on the POS REF page. The two IRS positions chosen are those exhibiting the least distance between them following comparison of each IRS position with the other two. 4-9 B747-400 FMS PILOT’S GUIDE Use or disclosure of the information on this page is subject to the restrictions on the title page of this document. The FMC navigation function gradually changes the computed FMC position from the triple-mix position to the single IRS position to prevent sudden position jumps. Ultimately the FMC position is equal to the single IRS position. The rate at which the position difference is eliminated is chosen to minimize aircraft maneuvers and map “jumps” while still ensuring all differences are eliminated upon reaching the pole for the worst case condition of flying directly North or South at maximum ground speed. When the computed aircraft position of both FMCs is between N83.5° and S83.5° latitude, the FMC returns to triple-mix IRS position updating. There is no instantaneous change in either FMC position when returning to triple-mix mode. Any differences existing between the mixed IRS position and either FMC position is washed out at the same rate used for previous 84° latitude crossing. If the triple-mix is not available (i.e., only one or two IRUs are valid), the “SPLIT IRS OPERATION” message is displayed. The POS REF page indicates the single or triple-mix IRS position. If there is a detected IRS failure while the FMC position is greater than 89° North or South latitude, the FMC position immediately becomes the IRS position. 4-10 Use or disclosure of the information on this page is subject to the restrictions on the title page of this document. B747-400 FMS PILOT’S GUIDE 4.5 HOLDING P PA A ATTERNS TTERNS This section is an in-depth look at holding patterns and how the FMC computes and calculates the holding pattern. 4.5.1 Types of Holding Patterns There are three types of holding patterns: 1. Patterns terminated by reaching a specific altitude (referred to as altitude terminated). 2. Patterns terminated by crossing the hold fix the first time after entering the hold (referred to as fix terminated). 3. Patterns terminated manually (referred to as manually terminated). All three types may exist in terminal area procedures extracted from the navigation database and thus can be accessed by the pilot. Only manually terminated holds may be created via the FMC HOLD page. Altitude terminated and fix terminated holds cannot be created via the FMC HOLD page. The altitude for altitude terminated holds is an AT or ABOVE constraint; therefore, altitude terminated holds only occur in climb. The FMC remains in the holding pattern until the AT or ABOVE constraint is met. If the aircraft is already at or above the specified altitude upon reaching the holding fix, the hold is not flown. Upon reaching the altitude constraint, the FMC enters the exit armed state, adjust the holding pattern size to provide the shortest route to the hold fix, and exits the hold the next time the hold fix is crossed. Fix terminated holds are allowed in all flight phases but are usually encountered in descent. This type of hold consists of only one loop (or partial loop) around the pattern and the FMC exits the hold upon crossing the hold fix the first time after entering the hold. No special displays are used to alert the pilot the hold is terminated. 4-11 B747-400 FMS PILOT’S GUIDE Use or disclosure of the information on this page is subject to the restrictions on the title page of this document. Manually terminated holds are allowed in all flight phases. The pilot must manually terminate this hold by selecting line 6R (EXIT HOLD prompt) on the FMC HOLD page. Upon selecting line 6R , the FMC enters the exit armed state, adjusts the holding pattern size to provide the shortest route back to the hold fix, and exits the hold the next time the hold fix is crossed. If a direct-to is executed while in any type of hold, the FMC exits the hold immediately. 4.5.2 Creation and Modification of Holding Patterns Pilot-generated holding patterns are created on the ACT RTE HOLD page which can be accessed by selecting the HOLD mode key on the CDU. If a hold does not already exist in the flight plan, this action displays the ACT RTE LEGS HOLD AT page which allows the pilot to specify a desired fix for the hold by entering the fix in line 6L
or to define a present position hold by selecting line 6R (PPOS prompt). If one or more hold(s) already exists in the flight plan when the HOLD mode key is pressed, the ACT RTE HOLD page is displayed which shows the characteristics of the nearest hold in the flight plan. The pilot may access the ACT RTE LEGS HOLD AT page, by selecting line 6L
(NEXT HOLD prompt). If more than one hold exists, the pilot may access the next nearest hold in the flight plan by selecting the NEXT PAGE key. Line 1L
of the hold page displays the fix at which the hold is defined. The holding quadrant and radial are displayed in line 2L
of the hold page. The quadrant abbreviations are N, NE, E, SE, S, SW, W, NW. Line 3L
of the hold page defines the inbound course and turn direction of the hold. For manually terminated holds, the inbound course defaults to the leg course of the leg preceding the hold fix and the turn direction defaults to right. The holding pattern’s straight leg size is defined by either its length or the time spent flying wings level. Line 4L
defines the leg time and line 5L
defines leg distance. Leg time and leg distance are mutually exclusive; an entry in either erases the value in the other. The FMC defaults to leg time. The leg time defaults to 1 minute at or below 14,000 feet and 1.5 minutes above 14,000 feet. The altitude used to compare to 14,000 is determined as follows: |