ILS Approach

James Albright (a former G450 driver)

Updated: 2013-11-09

The ILS approach remains the "go to" approach after all these years. (First tested in 1929 and installed operationally in 1941.) Refer to Instrument Landing System for background information about:

Regulatory Requirements
Equipment Requirements
Advantages and Disadvantages
Limitations

Everything here is from the references shown below, with a few comments in an alternate color.

Approach Category

If you have ASC 007 you are a Category C airplane unless you have a maintenance logbook entry raising your maximum landing weight. If you do not have ASC 007, you are a Category D airplane, end of discussion. See Approach Category for an explanation.

Approach Selection

Figure: Arrival Page, from G450 Aircraft Operating Manual § 2B-27-00, figure 37.

Approach selection is made either through the MCDU (NAV > ARRIVAL) or the NAV display.

There is an advantage to making this selection on the NAV display: if the appropriate chart is selected in green from the CHARTS page, future changes to the approach on the NAV display will automatically change the selected chart.

Preview & Auto-Tune

[G450 Aircraft Operating Manual §2B-05-50 2.A. (2)]

The PREVIEW submenu is used to select the NAV preview mode. The NAV preview mode permits the flight crew to select a short-range navigation (SRN) source for an SRN-based approach (VOR, ILS, MLS, etc.) while FMS (Long Range Navigation) is selected for display and providing lateral/vertical guidance. A long-range navigation source (FMS) must be the active navigation source in order for the PREVIEW prompt to be displayed.
When the necessary conditions are satisfied, the auto NAV preview functionality performs the following:
- Automatically selects the NAV preview mode
- Selects the SRN source for the approach procedure entered in the FMS flight plan
- Automatically sets the course on the display to the required in-bound course for the approach.
With auto NAV preview functionality, the flight crew is still required to arm the flight director for automatic transition from LRN (FMS) guidance to SRN guidance.
The EDS automatically selects the NAV preview mode when the following auto NAV preview enabling conditions are satisfied:
- The FMS is the selected NAV source
- The aircraft is within 75 NM flight plan distance and 30 NM direct distance from the destination airport
- An SRN approach is selected in the FMS flight plan
- Auto-tuning is enabled for the on-side NAV receiver
- The on-side SRN source frequency specified by the FMS approach is tuned by the FMS.

When the auto NAV preview conditions are satisfied, the NAV preview information is displayed on the PFD. When the NAV preview information is displayed, the flight crew can modify the SRN course or deselect the NAV preview mode altogether.

Alternatively, you can preset the localizer frequency and the approach back course. (This would be advisable if you expect to be on a complicated STAR with short vectors to ILS final, precluding the auto-tune function.) You would enter the ILS identifier into appropriate LSK in the PROGRESS page and the ILS approach course in the Display Controller PREVIEW submenu.

Localizer Mode Selection

Figure: LNAV Mode Selection, from G450 Aircraft Operating Manual, §2B-08-00, Pg. 7.

The book isn't very clear about this, but it is a basic function we've been doing for as long as we've had flight directors: use LNAV only for localizer only, APPR for an ILS.

Approach Armed

Figure: APR (Approach) Button, from G450 Aircraft Operating Manual, §2B-08-00, Pg. 11.

Pressing APR on the localizer/glide slope approach arms the glide slope and allows capture, ignoring the altitude select window.

Figure: ILS Approach Mode, from G450 Aircraft Operating Manual, §2B-08-00, Figure 30.

[G450 Aircraft Operating Manual, §2B-08-120, 20] The ILS approach mode automatically intercepts, captures, and tracks a front course localizer and glideslope beam, using the selected navigation source displayed on the coupled PFD. The ILS navigation source is selected using the display controller. The GS mode does not capture until after LOC has been captured.

Figure: ILS Approach Mode, from G450 Aircraft Operating Manual, §2B-08-00, Figure 31.

In blue needles (Long Range Nav) you should see the ILS identifier in the bottom right of the PFD. Should, but for some reason not always. Once in green needles (Short Range Nav) you should see the ILS identifier move to the NAV box on the right. Should, but again for some reason, not always.

Localizer Capture

Figure: ILS LOC Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 32.

[G450 Aircraft Operating Manual, §G450 OM 2B-08-120, 21] When the aircraft reaches the localizer beam sensor trip point, as shown below, the FGC automatically drops the heading select mode and switches to the LOC capture phase. The GS mode stays armed until the GS beam deviation is reduced to within the capture window.

Figure: ILS LOC Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 33.

Glide Slope Capture

Figure: ILS GS Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 34.

[G450 Aircraft Operating Manual, §2B-08-120, 22] When the aircraft reaches the vertical beam sensor trip point, the FGC automatically drops any other vertical mode that was in use and automatically generates a pitch command to track the glideslope beam. The FGC can capture GS from above or below the beam, as shown below.

Figure: ILS Glideslope Capture, from G450 Aircraft Operating Manual, §2B-08-00, Figure 35.

ILS Dual Couple Approach Mode

[G450 Aircraft Operating Manual, §2B-08-120, 23] During the tracking phase of an ILS approach, as shown below, the system uses landing aid flight path information from both the pilot and copilot PFD. This flight segment of the approach phase is automatically initiated and it occurs at 1200 ft radio altitude.

The dual couple mode PFD for the pilot and the copilot, shown below, requires that all of the following conditions are satisfied.

The pilot PFD NAV source must be NAV1, NAV2 or NAV3.
The copilot PFD NAV source must be NAV1, NAV2 or NAV3.
The pilot and copilot must have different NAV sources.
The PFD1/PFD2 NAV sources must both be tuned to the same LOC frequency.
The LOC/GS track mode is active.
The radio altitude is less than 1200 feet.
Both pilot sources are valid.
The PFD1 and PFD2 selected courses must be within two degrees.

At dual couple transition the following events occur:

Command bars are in view on both pilot and copilot PFDs.
The guidance panel PFD CMD button lights both L and R annunciators.

NOTES:

The PFD CMD button is inhibited in dual couple mode.
After canceling the APR mode the PFD CMD status reverts to the side that was selected before the dual couple transition.

In the dual couple mode, shown below, the high priority FGC (i.e., the FGC selected on the display controller (sensor page)) averages the radio data from the pilot and copilot NAV sources. If one navigation receiver fails, or if there is an unflagged miscompare between the NAV receivers, the approach mode continues. The high priority FGC sends identical FD commands (based on the average radio deviations) to both pilot and copilot PFDs in the dual couple mode.

Navigation failures in the dual couple mode result in the following automatic reconfigurations.

PFD1 NAV Fails -- The PFD CMD reverts to R. The approach mode continues using data from the PFD2 NAV source. If PFD1 NAV becomes valid, the dual couple mode automatically returns.
PFD2 NAV Fails -- The PFD CMD reverts to L. The approach mode continues using data from the PFD1 NAV source. If PFD2 NAV becomes valid, the dual CPL mode automatically returns.