Understanding GPS Substitution in VOR Approaches
AIM Section 1-2-3 allows GPS to substitute for VOR, NDB, and DME on instrument approaches. However, this substitution comes with a critical requirement that many pilots overlook.
Why Conventional VOR Approaches Still Matter
In an era dominated by GPS approaches, VOR approaches can offer lower minimums at specific airports. This makes mastery of VOR approaches valuable when weather is marginal.
| Approach Type | Runway | Minimum Altitude | Visibility | Notes |
|---|---|---|---|---|
| VOR 26 | 26 | 760 ft | 1 SM | Lower minimums |
| RNAV (GPS) 26 | 26 | 800+ ft | 1+ SM | Higher minimums |
These 40+ foot differences can be decisive when ceilings are right at minimums. At airports where VOR minimums are lower than GPS, knowing how to fly the VOR approach is an advantage.
Configuring Your G1000 for VOR 24 at KPOU
The VOR 24 approach at Poughkeepsie uses the Kingston VOR (IGN) as the primary navaid. Here's how to configure your G1000 to monitor both GPS and VOR guidance simultaneously.
Step 1: Access Bearing Options
On your Primary Flight Display (PFD), press the PFD softkey to access additional display options including bearing pointer configuration.
Step 2: Configure Bearing One
Select BRG1 and set it to NAV1, which should be tuned to the Kingston VOR (IGN, 117.6). You'll see a single-line bearing pointer (blue needle head) appear on your HSI.
Step 3: Verify Alignment
Observe your HSI. You should be tracking the 218° course inbound to the VOR, as specified on the approach plate. The bearing pointer is your verification tool—if it diverges from the GPS needle, investigate immediately.
Step 4: Divergence Protocol
If your VOR and GPS needles begin to diverge, prioritize the VOR needle as your primary guidance since this is a VOR approach. Significant divergence may indicate a database error, incorrect VOR frequency, or equipment malfunction. Consider a missed approach to re-evaluate.
Setting Up GPS Overlay on a VOR Approach (G1000)
On the MFD, press PROC and select the VOR approach from the destination airport procedure list. Before loading, tune NAV1 to the VOR frequency listed on the approach plate (for VOR 24 at KPOU, this is IGN 117.6). Identify the VOR audibly or verify the identifier on the HSI to confirm proper reception.
After loading the approach, press Activate on the MFD. On the PFD, verify the CDI source selector (bottom center of the HSI) shows GPS. The magenta GPS needle will now track the procedure, while NAV1 remains tuned to the ground-based VOR for required monitoring.
Press the PFD softkey, then select BRG1 and set the source to NAV1. A single-line bearing pointer (blue needle head) will appear on the HSI. Before the Final Approach Fix, confirm this bearing pointer aligns with the magenta GPS CDI needle. Divergence between the two after the FAF requires immediate action per your missed approach procedure.
Inside the FAF, AIM 1-2-3 requires continuous monitoring of the primary VOR navaid. Keep the bearing pointer visible on the HSI throughout the approach. If the VOR bearing pointer diverges more than a few degrees from the GPS needle, cross-check your NAV1 frequency, confirm VOR identification, and consider a missed approach if the discrepancy cannot be resolved before reaching minimums.
Real-World Application: When to Configure
While simulators allow on-the-fly adjustments, in actual flight you should configure your HSI and bearing pointers during a low-workload phase—typically during cruise, well before initiating the approach.
The RMI Needle: Your Verification Tool
The RMI (Radio Magnetic Indicator) needle is often overlooked, yet it's crucial for verifying your adherence to the VOR course. By allowing the flight director and autopilot to follow GPS guidance while simultaneously monitoring the RMI/bearing pointer, you achieve redundant navigation verification.
This technique—flying GPS while monitoring VOR—is exactly how airline pilots cross-check navigation systems. It builds the habit of never relying on a single navigation source.
Master VOR Approaches in the Simulator
Practice VOR approaches with GPS monitoring in our G1000 NXi simulator with airline pilot instructors.
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