Where a VOR gives an aircraft a single bearing to one ground station, GPS gives it a continuously computed position anywhere on earth, and RNAV builds on that position to fly point-to-point routes that don't need to pass over, or even near, any physical navigation aid at all. Understanding how the position is actually computed, and how confident the system is in that position, matters just as much as knowing how to punch a waypoint into the box.
A GPS satellite continuously broadcasts its own precise position and the exact time the signal was sent. A receiver measures how long that signal took to arrive and multiplies by the speed of light to get its distance from that satellite, a sphere of possible positions centered on the satellite. One satellite alone only narrows your position to a sphere; combining distance measurements from four or more satellites simultaneously narrows it down to a single point in three dimensions, plus a precise time correction for the receiver's own clock.
A basic GPS receiver, once it has a strong fix from enough satellites, computes latitude, longitude, altitude, groundspeed, and track continuously, updating many times per second, all without depending on ground-based infrastructure or line-of-sight to any single station. This is the core reason GPS coverage feels so much more uniform than VOR coverage, it isn't limited by terrain blocking a signal from one specific ground transmitter.
Receiver Autonomous Integrity Monitoring (RAIM) is the receiver's internal cross-check: with enough visible satellites, it compares redundant position solutions against each other to detect a faulty satellite signal before it corrupts the displayed position. If RAIM can't be assured, especially for an approach, the receiver will annunciate a warning, and the appropriate response is to not rely on GPS guidance for that specific purpose until the warning clears.
The Wide Area Augmentation System (WAAS) uses a network of ground reference stations that know their own exact position, compares that to what GPS reports, and broadcasts a correction via geostationary satellites, improving both accuracy and, critically, providing real-time integrity monitoring good enough to support vertically guided approaches. WAAS is what makes an LPV approach (Localizer Performance with Vertical guidance), with precision-like minimums, possible using GPS alone.
RNAV (Area Navigation) is a navigation method that allows an aircraft to fly any desired course within the coverage of relevant navigation aids, or within the accuracy limits of self-contained systems, rather than being restricted to flying directly to or from a single ground station. GPS is the dominant RNAV sensor today, but RNAV as a concept predates GPS and historically included systems like inertial navigation and VOR/DME- based computed positions.
| Approach line | Guidance | Typical minimums |
|---|---|---|
| LPV | Lateral + WAAS-based vertical guidance | DA, can approach ILS-like minimums |
| LNAV/VNAV | Lateral + baro-VNAV vertical guidance | DA, temperature-limited |
| LNAV | Lateral guidance only | MDA, non-precision |
| LP | Lateral only, WAAS-based, tighter than LNAV | MDA, used where terrain limits vertical guidance |
A single approach chart often lists all four minimums lines together, and which one a pilot flies to depends on their specific avionics' certified capability, not personal preference.
A GPS flight plan is simply an ordered list of waypoints, five-letter named fixes, VOR identifiers, airports, or user-defined points, that the receiver sequences through automatically, computing course, distance, and time to each in turn. This is what makes direct-to navigation between arbitrary points, not just VOR-to-VOR routing, practical for everyday cross-country flying.
GPS can be degraded or lost entirely, from satellite issues, receiver failure, or (increasingly relevant in some regions) intentional jamming or spoofing. This is precisely why the FAA maintains VOR as a deliberately retained backup network (the Minimum Operational Network) and why pilots are trained to recognize a GPS position that looks implausible and cross-check it against other sources rather than trusting it blindly.
Before GPS, cross-country navigation meant flying a chain of VOR-to-VOR legs, or careful pilotage and dead reckoning between checkpoints, both of which constrained routing to what the ground infrastructure or visible landmarks allowed. GPS-based RNAV lets an aircraft fly the actual shortest useful path between any two points, which is why direct routing is now the norm rather than the exception for VFR and IFR flight alike.
Planning a cross-country from KABC to KXYZ: rather than routing VOR-to-VOR, the flight plan is built as a short sequence of waypoints, departure airport, a couple of named enroute fixes chosen for airspace or terrain reasons, and the destination, with the GPS computing distance, course, and ETE for each leg automatically and sequencing through them in order. A VOR cross-check partway along the route confirms the GPS position agrees with an independent source.
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This guide is intended for educational and training purposes only. It is not a substitute for official FAA publications, an authorized ground school, or qualified flight instruction, and should not be used as a sole source for real-world flight planning, dispatch, or operational decisions.