Instrument rating · ACS IR.V.A
Intercepting and Tracking Courses and DME Arcs
This lesson covers finding your position, intercepting and tracking courses with VOR and GPS, and flying a DME arc.
Why this one matters
Navigation errors in IFR put airplanes off the protected airspace that keeps them clear of terrain. A wrongly tuned station, a reversed needle, or a GPS flight plan that wasn’t checked all look fine until they don’t. Knowing your position and verifying your equipment is what turns navigation from following a needle into knowing where you are.
Can’t miss
- •Tune and identify every ground navaid by its Morse code. No identifier means don’t use it.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
- •Before intercepting, know where you are relative to the station or waypoint: which radial, which side, how far.(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- •Intercept angle: usually 30° to 45°; up to 90° when far off course; less close to the station, and no more than about 30° onto a localizer. Lead the rollout as the needle starts to center.(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- •Track by bracketing: find a heading that holds the needle centered, then make smaller corrections.(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- •DME arc: turn onto it about ½ nm early at groundspeeds of 150 knots or less (more lead when faster), keep the bearing near the wingtip with small heading changes, and leave it on the lead radial.(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- •GPS: verify the flight plan, the database, the CDI source, the active leg and the mode annunciation. Non-WAAS units need a RAIM prediction; watch for integrity alerts and GPS interference NOTAMs.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
- •Checkride standard: course within ¾-scale CDI, DME arc ±1 nautical mile, altitude ±100 feet, heading ±5°.(Instrument Rating ACS (FAA-S-ACS-8C), IR.V.A.S5-S6)
What you should know
Ground-based navigation K1
- Set the course, check TO/FROM, and orient: with the course set close to your heading, the needle points toward the course.(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- Reverse sensing: flying a VOR course with the opposite TO/FROM (or a localizer back course on a CDI) makes the needle work backward. An HSI set to the front course avoids it.(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- DME is slant range: at least 1 mile from the station per 1,000 feet of altitude, the error is negligible.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
- DME arc with an RMI: keep the bearing pointer cycling between about 5° and 10° behind and ahead of the wingtip; if you drift ½ nm off the arc, correct 10° to 20° toward it. Wind changes how often. Leave the arc at the lead radial (charted, or a few degrees early at 150 knots or less).(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- Station passage: approaching a VOR the needle gets more sensitive, then the cone of confusion makes it swing and the TO/FROM flips. A GPS shows passage when it sequences to the next leg.(Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems)
- For IFR, the VOR must have been checked within the preceding 30 days: ±4° on a VOT or ground checkpoint, ±6° airborne, 4° between two receivers; logged with the date, place, bearing error and signature.(14 CFR 91.171)
- Many VORs are being shut down; a minimum operational network (MON) of VORs remains. Check NOTAMs for outages.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
Satellite navigation K2 · R3
- GPS for IFR must be installed and approved, with a current database for approaches.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
- RAIM checks the satellites agree: fault detection needs 5 satellites (or 4 with baro-aiding), and fault exclusion 6 (or 5 with baro-aiding). A non-WAAS unit needs a preflight RAIM prediction, and an alternate means of navigation for the route. WAAS adds its own integrity monitoring. If integrity is lost in flight, tell ATC and use the other means.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
- GPS can be jammed or spoofed. Watch for NOTAMs and integrity alerts, and keep a ground-based backup when you can.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
- GPS CDI full scale: ±2 nm en route (±5 nm on older non-WAAS units), ±1 nm in the terminal area within 30 nm of the airport, ramping to ±0.3 nm (or angular) from 2 nm before the final approach waypoint. Manually changing the sensitivity can cancel approach mode.(AIM, Chapter 1 (navigation aids, GPS and WAAS))
Managing the box R1 · R2
- Check the active waypoint, the course and the CDI source (GPS or VLOC) after every change. Use the MFD map to confirm where the navigator thinks you are.(Advanced Avionics Handbook (FAA-H-8083-6))
- With the autopilot: select the nav mode, confirm it is armed and then captures (active) on the annunciator, and watch the first intercept; if it doesn't do what you expect, fly heading mode or hand-fly.(Advanced Avionics Handbook (FAA-H-8083-6))
- If programming takes your eyes off the instruments too long, fly a heading first, then program.(Advanced Avionics Handbook (FAA-H-8083-6))
- If a navaid or GPS fails, tell ATC.(Instrument Rating ACS (FAA-S-ACS-8C), IR.V.A.S7)
On the flight
ACS standards
- Maintain airspeed ±10 knots, altitude ±100 feet, and selected headings ±5°.(Instrument Rating ACS (FAA-S-ACS-8C), IR.V.A.S5)
- Maintain a course with no more than ¾-scale CDI deflection; on a DME arc, maintain the arc ±1 nautical mile.(Instrument Rating ACS (FAA-S-ACS-8C), IR.V.A.S6)
What your instructor is watching for
Your instructor watches for tuning and identifying every time, a correct picture of your position, a clean intercept, wind correction, and the right CDI source.
Scenarios
Decide what you would do first, then see the worked answer.
Flying a VOR course, the needle moves the opposite way to your correction.
What’s wrong? See the worked answer
Probably reverse sensing: TO/FROM doesn’t match my direction. Reset the course to match where I’m going.
Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems
Your CDI is centered, but you’re far from where the map shows you should be.
What do you check? See the worked answer
The CDI source (GPS vs VLOC), the active waypoint, and whether the navaid is identified.
Advanced Avionics Handbook (FAA-H-8083-6)
On a 10 DME arc with a crosswind pushing you toward the station.
What do you expect? See the worked answer
I’ll need fewer turns toward the station and may need to turn away. Keep it within ±1 mile.
Instrument Flying Handbook (FAA-H-8083-15B), Navigation Systems
Common mistakes
Not identifying the station.
It may be off the air or a different station.
Instead: Listen to the Morse code.
Wrong CDI source.
You follow the wrong needle.
Instead: Check GPS or VLOC every time.
Chasing the needle.
You zigzag.
Instead: Find a heading, then bracket.
Now train it
Say it out loud, hear it asked, and take the quick check in this lesson’s practice pack. It tracks your shaky spots.
Got it?
When it feels solid, practice intercepting and tracking courses and dme arcs out loud with our examiner.
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Go to the source (free)
Teaching this? The instructor lesson plan →
Sources
- Instrument Flying Handbook (FAA-H-8083-15B): Navigation systems
- Instrument Procedures Handbook (FAA-H-8083-16B): Departures; en route; arrivals
- Aeronautical Information Manual (AIM): Chapters 1, 4, 5 and 7
- Instrument Rating ACS (FAA-S-ACS-8C): Area V
Study aid, not FAA guidance. Regulations change; check the current text at eCFR and the ACS. Checked against current sources 2026-11-13.