Learn how to fly a DME arc in a flight simulator: tune the station, lead the intercept, hold distance, correct drift and exit on the right radial.
To fly a DME arc in a flight simulator, tune and identify the specified DME station, intercept the published distance with a lead turn, then fly a tangent heading while making small turns towards or away from the station. Monitor DME continuously and leave the arc at the charted radial.
This general method works in Microsoft Flight Simulator, X-Plane, FSX and Prepar3D. A DME arc is based on indicated distance from a particular station, so follow the procedure chart rather than drawing an approximate circle around the airport. Our broader IFR briefing and avionics workflow explains how charts, navigation sources and mode checks fit together.
What should I set up before intercepting a DME arc?
Before intercepting the arc, identify its centre station, radius, direction, entry route, minimum altitude and exit radial. Most training arcs are centred on a VOR/DME or VORTAC, but DME itself provides distance only; radial information must come from the associated VOR, another charted aid or a suitable flight-management display.
- Tune and identify the station: select the published frequency and confirm the identifier rather than trusting the displayed name alone.
- Confirm the distance source: make sure the DME readout belongs to the station defining the arc, not the destination airport, an active GPS waypoint or the other NAV receiver.
- Select the correct NAV source: use VLOC or NAV for conventional VOR raw data. GPS mode will not make a VOR CDI behave correctly.
- Set the entry radial: rotate the OBS to the radial on which the aircraft will enter, normally with a FROM indication.
- Stabilise early: reach the required altitude and a manageable speed before the intercept so that power, trim and configuration changes do not disrupt the turn.
If CDI sensing, station identification or TO/FROM indications are unfamiliar, our VOR/DME tuning and CDI-sensing guide covers those foundations.
How do I fly a DME arc manually?
The manual method is to lead the intercept, establish a tangent track and use small heading changes to control the DME trend.
- Approach on the published entry route. Confirm that the DME is moving towards the arc value when approaching from outside. Maintain the charted altitude and do not cut inside the protected entry path.
- Calculate a starting lead. A useful rule of thumb is 0.5 per cent of groundspeed in nautical miles. At 120 knots, that gives about 0.6 NM. For a 15 DME arc approached from outside, begin the turn near 15.6 DME. Bank angle, wind and intercept geometry can require adjustment, so treat this as a starting estimate rather than an exact figure.
- Turn onto the tangent heading. In still air, a clockwise arc uses approximately the current radial plus 90 degrees; a counter-clockwise arc uses the radial minus 90 degrees. On a clockwise arc the station remains on the right, while on a counter-clockwise arc it remains on the left.
- Check the rollout. The aircraft should reach the required DME as it settles onto the tangent. If the distance is already increasing rapidly, the lead was late or the turn too shallow. If it drops well inside the arc, the turn began too early or used too much bank.
- Track successive radials. Advance the OBS by 5 or 10 degrees in the direction of travel. As each radial approaches, change heading by roughly the same amount to follow the curve. The familiar twist-and-turn technique helps measure progress, but DME—not CDI deflection—is what controls the radius.
- Correct for wind. A crosswind changes the heading needed to maintain the arc. Establish a wind-corrected tangent and make small additional turns when the DME develops a steady trend away from the published value.
For example, at the 090 radial on a clockwise arc, the no-wind tangent heading is approximately 180 degrees and the station should be off the right wing. Actual heading may differ because the aircraft must crab into the wind.
Common DME arc errors and corrections
The DME trend tells you whether the aircraft is drifting outside or inside the arc; the CDI primarily shows which radial the aircraft is crossing.
| Indication | Likely cause | Correction |
|---|---|---|
| DME rises steadily above the arc | The aircraft is drifting outside, often because of wind or an insufficient turn | Turn 5 to 10 degrees towards the station, then ease back towards a tangent heading before reaching the target distance |
| DME falls steadily below the arc | The aircraft is cutting inside the circle | Turn slightly away from the station, then re-establish the tangent as the distance recovers |
| Large repeated distance swings | Corrections are too large or held too long | Use smaller heading changes and watch the trend over several seconds rather than chasing every tenth of a mile |
| CDI sensing appears reversed | The reciprocal course is selected, the indication shows TO rather than FROM, or GPS is the active source | Set the station radial with a FROM indication and verify the NAV source |
| DME is blank, frozen or implausible | The wrong receiver, station or display field is selected | Retune, identify and verify which receiver supplies the distance. For glass-cockpit faults, use our MSFS G1000 and FMS control checks |
A small DME cycle during segmented turns is normal. A mistake we see constantly is correcting every 0.1 NM immediately, which produces an unstable series of S-turns instead of a controlled arc.
Can the autopilot fly a DME arc?
An autopilot can hold the headings used to fly an arc, but conventional VOR NAV mode cannot maintain a constant DME radius by itself. NAV mode tracks one selected radial, which is a straight line to or from the station rather than a circular path.
Use heading mode and move the heading bug in small increments when practising a raw-data arc. GPS or LNAV may fly the arc automatically only when the loaded procedure contains a correctly coded arc path and the aircraft's navigation system supports it. Verify the displayed path, active leg, GPS source and mode annunciation before relying on automation.
When should I leave the DME arc?
Leave the arc at the published exit or lead radial, allowing enough turn anticipation to intercept the next course without overshooting it. If the chart provides a lead radial, use it; otherwise, estimate the lead from groundspeed, bank angle and the size of the heading change.
Pre-tune the outbound VOR, localiser or approach course on a second receiver when available. Retuning the only receiver too early can remove either the DME distance or the radial information still needed to finish the arc. Do not descend merely because the aircraft has left the arc—remain at the charted altitude until the procedure authorises descent.
Why does DME disagree with the simulator map or GPS?
DME measures slant range directly between the aircraft and the ground station, while a map or GPS waypoint may show horizontal or great-circle distance. The difference becomes more noticeable when the aircraft is high and close to the station.
For a published DME arc, fly the indicated DME value unless the procedure or aircraft documentation specifies another source. Also check that the GPS waypoint and DME facility represent the same physical station; similarly named airport, VOR and runway fixes are not necessarily co-located.