-
Rule 3: If a VOR is required to be tuned to get position, it is tuned.

 -
Rule 4: If the active leg specifies a VOR, VOR/DME, VORTAC, DME, TACAN or non-collocated VOR/DME or VORTAC, this is tuned and displayed.

 -
Rule 5: If the active waypoint is a VOR, VOR/DME, VORTAC, DME or non-collocated VOR/DME or VORTAC and the aircraft is within the figure of merit, then this active WPT is tuned. Else, the same test with any down path waypoint is made. If yes, the closest of these waypoints is tuned. Else, the same test with the FROM waypoint is requested. If the answer is positive, the FROM waypoint is tuned.

 -
Rule 6: The nearest VOR/DME or VORTAC, collocated or non-collocated, to the aircraft that is within its figure of merit is tuned and displayed.

 -
Rule 7: The nearest VOR to the aircraft that is within its figure of merit.

 If no VOR satisfied these 7 rules, then, no VOR is tuned. By the first 5 rules, a DME may be tuned at the same time. If a VOR is tuned by rule 1 and another (different) is requested by rule 2 or rule 3, then the message TUNE BBB FFF.FF is displayed, where:
 -BBB is the requested navaid,
 -FFF.FF is the corresponding VOR frequency.
 NOTE : For the rule 2:
____ If the specified VOR or VOR/DME is tuned and is not available (neither VOR nor DME is received), then a message is displayed on both MCDUs and the ND: SPECIF VOR-D UNAVAIL.
 (b) ILS tuning The rules for ILS tuning described hereafter apply only. As for VOR tuning, ILS tuning follows rules hierarchically defined from 1 to 3. ILS tuning means frequency and course.

 1 Rule 1:
_ An ILS, LOC only, IGS, LDA, or SDF has been manually tuned by the pilot.
 2 Rule 2:
_ If the active flight phase is PREFLIGHT or TAKEOFF and if the TAKEOFF runway has an ILS or LOC only associated with it, then this ILS is tuned.
 3 Rule 3:
_ If the flight phase is CLB or CRZ or APPR or DES or GO AROUND and if the F-PLN approach type is ILS, LOC only, IGS, LDA, SDF or ILS Back Beam, then the approach ILS is tuned. If an ILS is tuned per rule 1 and another station is requested by rule 2 or 3 and the ILS's (frequency or course) do not match, then the RWY/LS MISMATCH message is displayed.
 (c) DME tuning Up to four DME frequencies may be sent to each DME (f1, f2, f3, f4). f1 is the displayed frequency (also called fd). f2, f3 are the DME frequencies used for position computation. f5 is the ILS/DME frequency (also called fls).
 1 fd (or f1) is tuned by the logic of VOR tuning. If by this
_ logic no DME is selected, fd is not assigned.
 2 fls (or f5) is tuned by the logic of ILS tuning. If by this
_ logic no DME is selected, fls is not assigned.
 3 f2 and f3: f2 and f3 are used for computation of DME/DME
_ position and are tuned on request by the system.
 (d) ADF tuning An ADF frequency is tuned if the following conditions (hierarchically defined from 1 to 4) are satisfied:
R 1_An ADF has been manually selected.
 2 An NDB is specified for the approach (e.g. NDB approach and
_ the active leg is in the approach).
 3 In any area, if the TO waypoint in the F-PLN is an NDB, this
_
 NDB is autotuned.

 4 In any area, if the FROM waypoint in the F-PLN is an NDB, this
_
 NDB is autotuned.

 When an ADF is autotuned by rule 2 above, it shall remain tuned until an another ADF is manually tuned or until the following condition is true: (rule 2 is no more true for that ADF) and (another ADF is tuned by one of the above rules). When an ADF frequency is tuned, BFO is not automatically selected, but the pilot can select BFO:
R - If an NDB is manually tuned and another NDB is requested by R autotuning rule 2, then the TUNE BBB FFF.FF message is displayed.
 -If flying and NDB approach with a procedure specified NDB and that NDB has been deselected, then the SPECIF NDB UNAVAIL message is displayed.
R
 D. IR Alignment
 (Ref. Fig. 018)

 (1)
 General Alignment of the IRS starts when the OFF/NAV/ATT selector switch on the Mode Selector Unit (MSU) is in the NAV position. IRS ALIGNMENT calculations may only be carried out on ground before takeoff and after pilot entry of the current A/C coordinates. This entry results from a pilot action either (as basic means) on the MCDU INIT A page or (as optional means) on the ISDU (Inertial System Display Unit). If an entry is done on the ISDU, the FMGC (FM part) receives the ARINC label from the IRS with the NO IRS Initialization digital discrete (bit 22, label 270) reset to zero; so the FMGC knows that a position has been sent to the IRS. The following cases may appear:

 (2)
 Normal case The three MSUs are in NAV mode, IRs are in Alignment Status. On the MCDU INIT A page, the origin entry displays the airport coordinates (LAT/LONG). An ALIGN IRS prompt appears then. Pressing this prompt selects the displayed position and sends it to the IRS in Alignment Status; ALIGN IRS is then cleared. Coordinates are entered separately on the ISDU, the position is immediately sent to the IRS which are in Alignment Status. The LAT and/or LONG is echoed to the FMGC on labels 041 and 042, respectively, and are thus displayed on the INIT A page on the MCDU. Entry of a position via the ISDU, while the ALIGN IRS prompt is displayed on the MCDU, also clears this prompt.
　
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