Fly area-navigation courses and curved DME arcs — and know what the box is (and isn't) telling you.
Area navigation (RNAV) lets you fly directly between defined waypoints rather than station-to-station. A panel-mount GPS computes your position from the satellite constellation and draws the desired track as a magenta line; cross-track error replaces the old CDI deflection (now scaled in nautical miles, and tighter as you approach an airport). Integrity comes from RAIM (receiver autonomous integrity monitoring) on a basic GPS, or from WAAS, which adds a correction and integrity signal precise enough to support vertical guidance (LPV). Always confirm the database is current and the unit has acquired an adequate position with integrity before relying on it for IFR.
Most units auto-sequence waypoints in LEG mode — the box steps to the next leg as you pass each fix. OBS / suspend holds the active waypoint so you can fly a procedure turn or hold without the unit sequencing past it. Mismanaging the mode is one of the most common GPS errors: if the box won't sequence, check whether SUSP/OBS is active; if it sequences when you didn't want it to, you forgot to suspend. Brief which mode you need before each segment.
| Step | What you do |
|---|---|
| Lead the turn onto the arc | Begin the turn to the arc about ½ nm before the arc distance (a lead based on groundspeed), rolling out roughly 90° to the station bearing. |
| Turn ten / twist ten | Keep the bearing pointer near the wingtip; each time it falls ~10° behind, turn 10° toward the station and re-set the next reference radial. |
| Correct for distance | If you drift outside the arc, turn slightly toward the station (and vice-versa); a crosswind needs a small wind-correction bias. |
| Lead the radial off the arc | Lead the turn onto the final/inbound course so you roll out established, not overshooting. |
With an RNAV system, an arc may be charted as a constant-radius leg and the GPS simply draws the curve — but you must still understand the raw-data technique, because GPS distance is over the ground while DME is slant range, and the two read differently close-in and at altitude.
A suitable IFR GPS may generally be used in lieu of DME and ADF — for example to fly a DME arc or identify a fix — provided the underlying facility/fix is in the current database and the installation is approved. This does not let you substitute GPS for the primary NAVAID that defines a ground-based approach unless the procedure or AIM permits it. Know your installation's limitations and the current AIM guidance, and brief any substitution before you need it.
Curated reference clip — “What Do You Know About RNAV Approaches? | RNAV GPS Approach | IFR Training,” FlightInsight (YouTube), verified via oEmbed. Embedded with the creator's player; we don't host or alter it.