GPS for Part 135 | Navigating the Sky with Precision 

GPS Operations 

For Part 135 pilots, precise navigation is more than a convenience—it’s a necessity. From managing customer expectations to meeting FAA regulatory requirements, accurate navigation ensures the safety, efficiency, and reliability of operations. At the center of modern aircraft navigation lies one critical tool: GPS. While GPS simplifies many aspects of flying, it also requires a solid understanding of its concepts, tools, and limitations to use it effectively. 

Why GPS is Critical 

Part 135 operations often involve flying into and out of challenging airfields, adapting to unique customer requests, and meeting precise schedules. GPS provides the flexibility and precision needed for these tasks. With capabilities such as pinpoint lateral and vertical navigation, expanded access to airports lacking ground-based navigation aids, and enhanced safety during low-visibility approaches, GPS has become a trusted partner for pilots. 

However, proper use of GPS requires more than just turning on the avionics. Understanding its principles and limitations is essential to avoid errors, especially when faced with RAIM limitations, outdated NOTAMs, or equipment malfunctions. 

Essential GPS Concepts 

1. RAIM (Receiver Autonomous Integrity Monitoring): RAIM ensures the GPS signal’s accuracy by detecting faults in satellite data. Pilots must verify RAIM availability for IFR operations to ensure consistent signal reliability during enroute and approach phases.
2. RNP (Required Navigation Performance): RNP defines the precision needed for specific airspace or procedures, combining lateral and vertical accuracy and integrity requirements. Familiarity with RNP helps Part 135 pilots fly tailored procedures, such as RNAV approaches, with confidence.
3. Noise, Bias, and Orbital Errors: GPS signal integrity might degrade due to natural noise, signal bias, or satellite orbital errors. While WAAS and GBAS mitigate many of these discrepancies, understanding their causes allows you to take corrective actions when unexpected deviations occur.
4. WAAS (Wide Area Augmentation System) and GBAS (Ground-Based Augmentation System): These systems enhance GPS accuracy by correcting signal errors in real-time. WAAS is particularly valuable in providing vertical guidance for small airports, while GBAS supports precision approaches at major hubs.
5. GPS NOTAMs: GPS NOTAMs alert pilots to GPS outages or abnormalities in specific regions. Regularly reviewing these ensures you’re not caught off guard mid-flight, particularly during critical phases like approaches.
6. STAR (Standard Terminal Arrival Route) Procedures: STARs rely heavily on GPS-enabled RNAV for efficient routing into complex airspace. Safeguard accuracy by cross-referencing loaded procedures in the FMS before execution.
7. Fly-Over vs. Fly-By Waypoints: Learn to distinguish between these waypoint types on your GPS to avoid navigation errors. Fly-by waypoints allow smoother transitions by preemptively adjusting the flight path, while fly-over waypoints require passing directly over a location before turning.
8. Localizer Performance (LP): GPS enables lateral precision similar to an ILS localizer, offering more options for approaches at smaller or remote airports.
9. Lateral and Vertical Navigation (LNAV/VNAV): GPS simplifies the task of maintaining prescribed altitudes and track lines, especially during RNAV approaches or STAR procedures.

Tools and Techniques for GPS Accuracy 

Getting the most out of GPS technology means arming yourself with the right tools and best practices. Here’s a quick checklist for ensuring safe navigation using GPS: 

• Pre-Flight RAIM Checks: Verify RAIM availability for your planned route to prevent in-flight surprises. 

• Database Currency: Ensure you’re operating with the most up-to-date navigation database to avoid STAR procedure errors or unrecognized waypoints. 

• Monitor GPS NOTAMs: Always review NOTAMs that may impact signal availability or WAAS/GBAS corrections in your area. 

• Review Operational Guides: Familiarize yourself with specific aircraft operating manuals and GPS limitations. This can prevent errors caused by exceeding equipment capabilities. 

• Back-Up Procedures: Always have a secondary navigation plan in case of GPS signal degradation or equipment failure. 

• Practice Fly-By and Fly-Over Waypoint Execution: Misinterpreting waypoint types can lead to significant deviations, especially in STAR procedures. 

Mastering STARs and RNAV Approaches 

STAR procedures demand precision, particularly when using RNAV or GPS navigation. Start by cross-referencing all procedure information in your FMS and GPS unit, ensuring accurate sequence loading. Pay attention to whether a waypoint is “fly-over” or “fly-by,” as this affects how the aircraft transitions between legs. 

When flying RNAV approaches, remember that WAAS capabilities allow you to treat lateral guidance similarly to traditional ILS. Beyond LNAV, approaches with LPV (Localizer Performance with Vertical Guidance) provide extra precision, often allowing the use of lower minimums. 

The Bigger Picture 

For pilots, GPS is far more than a convenience—it’s a pathway to safer, smarter, and more flexible operations. By mastering the principles behind this technology and staying vigilant with updates, NOTAMs, and procedures, you can leverage GPS to its full potential. Your aircraft’s navigation is only as capable as your knowledge and application of the tools you have.