RNAV(GPS) Approach

James Albright (a former G450 driver)

Updated: 2013-11-04

The RNAV(GPS) approach will soon be — if it isn't already — the most popular approach in the world. If you find one with LPV minimums, you've got it made. Refer to RNAV (GPS) for help with approach selection.

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 G450 Approach Category for an explanation.

Approach Selection

Photo: MCDU arrival page (KASH), from Eddie's aircraft.

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.

G450 Operational Approval

[G450 Aircraft Operating Manual §1-34-30 ¶3.] Approaches:

a. Approved Procedures

RNAV (GPS) or RNAV (GNSS)
RNAV (RNP)
GPS
VOR/DME RNAV
VOR*
VOR/DME*
TACAN
NDB*

*Approaches above, suffixed with an asterisk, may be flown with FMS guidance provided the appropriate civil aviation authority has approved such operations. See that country’s Aeronautical Information Publication, or AIP, to confirm approval. In the US, AC 90-108 advises that RNAV systems cannot be used as a substitute for the navaid lateral guidance during the final approach segment.

Can you fly an RNAV (GNSS) approach?

Probably: see RNAV (GNSS) Example.

b. Limitations and Exceptions:

The final segment of the approach must be flown with the FMS in the Approach Mode. DR or DEGRADE annunciators cancel the Approach Mode.
For airplanes having ASC 059B (or later approved revision), RNAV (GPS) or RNAV (GNSS) approaches can be executed to LPV minima. When loading an approach with LPV minima into the FMS, either graphically or using the MCDU, the FMS will default to the LPV criteria. Removing the LPV criteria from the FMS in order to perform the approach using LNAV or LNAV / VNAV minima can be done only using the MCDU. With the LPV mode captured, it is recommended that transition to LNAV minima or a go-around be performed if the LPV Unavailable caution CAS message displays.
NOTE: EGPWS Mode 6 must be operable and the associated audio call outs not inhibited, when performing RNAV (GPS) approaches to LPV minima.
Prior to conducting RNAV (RNP) approaches with Authorization Required (AR), appropriate operational approval (i.e., Operations Specifications (OpsSpecs), Letter of Authorization (LOA), or Management Specifications (Mspecs)) must be obtained. Requirements and operational guidance are found in AC 90-101, and in the Gulfstream RNP AR Operations Manual, GAC-OIS-02 or GAC-OIS-07 (basic issue or later approved revision).

c. For airplanes having ASC 059B (or later approved revision), RNAV (GPS) approaches can be executed to LPV minima. When loading a RNAV (GPS) approach with LPV minima into the FMS, either graphically or via the MCDU, the FMS will default to the LPV criteria. Removing the LPV criteria from the FMS in order to perform the approach using LNAV or LNAV/VNAV minima can be done only on the MCDU. With the LPV mode captured, it is recommended that transition to LNAV minima or a go-around be performed if the amber LPV Unavailable caution CAS message appears.

d. For airplanes having ASC 059B or (later approved revision) with SBAS receivers), SBAS-enabled GPS navigators are in compliance with TSO-145c/146c.

[G450 Aircraft Operating Manual §1-34-30 ¶3.] Non-WGS-84 Airspace / Countries Partially Compliant with WGS-84: When operating in non-WGS-84 airspace or in countries where the airspace is partially compliant with WGS- 84, the FMS with GPS position updating meets the required navigation accuracy and may be used for SIDS, STARS and en route navigation. When flying ILS, VOR or ADF approaches and missed approach procedures in these two situations, the GPS updating does not need to be inhibited or deselected provided the appropriate raw data is used throughout the approach and missed approach as the primary navigation reference. For countries that are partially WGS-84 compliant, when RNAV (GNSS) approaches are offered, these approaches may be flown using the FMS with GPS position updating provided the approach chart is annotated with “PANS OPS”.

This bit of advice has changed over the years. For a G450 you can generally navigate en route, fly departures and arrivals on GPS any place in the world. You can fly approaches using GPS in countries that are WGS-84 compliant. For countries that are not compliant, or partially compliant, look for "PANS OPS" on the chart. RNAV (GNSS) approaches will require a bit more research on your part. See:

FMS Strategy

If the RNAV (GPS) approach includes LNAV/VNAV minimums, you can use the APCH mode of the FMS. If LNAV/VNAV minimums are not included, you can still use the APCH mode, but it will be up to you to honor the MDA as a hard altitude. Once cleared the approach, set the FAF altitude in the altitude selector window. Once inbound to the FAF, select APCH and set the missed approach altitude.

Guidance panel operation will have a major impact on FMS and autopilot performance during the approach...

Do not “Preview” a course if planning an RNAV approach; the approach will not arm correctly and may instead attempt to intercept the raw data represented by the previewed course.

KSAV RNAV (GPS) Rwy 10 Example

Cleared to TILEE — Set altitude preselect to 2600' and select LNAV/VNAV

Once level at 2600' on course
If flying to MDA, set altitude preselect to MDA; you want the system to honor the MDA
If flying to DA, set altitude preselect to FAF altitude (2000'); you don't want to go beyond the FAF unless the system goes to approach mode
Select “App Arm”
If flying to MDA: after the FAF and once the runway is in sight (EVS or visual); set the missed approach altitude
If flying to DA: when the FAF goes magenta (becomes the “to” waypoint) and once “APP ARM” appears; as soon as you get the green VGP, you can set the missed approach altitude

References:

Advisory Circular 90-101, Approval Guidance for RNP Procedures with SAAAR, 12/15/05, U.S. Department of Transportation

Advisory Circular 90-108, Use of Suitable Area Navigation (RNAV) Systems on Conventional Routes and Procedures, 3/3/11, U.S. Department of Transportation

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream G450 Aircraft Service Change 007C, Maximum Landing Gross Weight, 58,500 pounds, Category C, Provisions, October 26, 2011

Gulfstream G450 Aircraft Service Change Number 059B, Enhanced Navigation, December 22, 2011

Gulfstream G450 Operational Information Supplement, G450-OIS-02, Contaminated Runway Performance, Revision 1, August 3, 2011