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Instrument rating · ACS IR.V.A · lesson pack

Intercepting and Tracking Courses and DME Arcs

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.

1 · Know these cold

  • •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)

2 · The lesson

Ground-based navigation
  • 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
  • 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
  • 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)

Want it all on one page, with scenarios? Read the full lesson.

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.

3 · Say it out loud

Answer each one out loud, then check yourself and mark how it went.

  1. Remember Recall it

    “What is a typical intercept angle?”

  2. Understand Explain why

    “Why does DME read more than your ground distance when you’re over the station?”

  3. Apply Use it on a flight

    “Your GPS shows an integrity alert halfway to your destination. What do you do?”

4 · 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.

5 · Quick check

Answer, then reveal. Flag anything you want to see again.

  1. 1. How do you confirm a VOR is the right one and working?

  2. 2. What does RAIM do?

  3. 3. DME arc tolerance on the checkride?

  4. 4. When is DME slant-range error negligible?

  5. 5. Course tolerance on the checkride?

  6. Scenario6. A NOTAM warns of GPS interference along your route. What do you plan?

Trained it? Now prove it: practice intercepting and tracking courses and dme arcs out loud with our examiner.

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Connect it

One situation that runs across this lesson and its neighbors in the same ACS area. Decide first, then check.

Connect it · Navigation Systems

The departure procedure needs 300 feet per NM to 3,000 feet MSL, then an arc to join the airway. On a hot day you expect 100 knots groundspeed in the climb.

Can the airplane meet it, and how do you fly the arc? Decide, then see the worked answer

Feet per minute = gradient × groundspeed ÷ 60, so 300 × 100 ÷ 60 = 500 fpm, and you have to sustain it all the way to 3,000 feet MSL, not just after liftoff. Check the POH climb performance at your actual weight and that day's density altitude for the whole climb. If the airplane can't sustain 500 fpm with margin, don't depart on that procedure: take a different departure, wait for cooler air, or lighten the airplane. Joining the arc: lead the turn, about 0.5 NM at 150 knots or less, turn about 90° onto the arc, and watch the DME for an overshoot or undershoot. Flying it with an RMI: keep the bearing pointer on the wingtip reference; let it drift 5° to 10° behind, then turn about 10° toward the station until it's back on the wingtip. If you're off the arc, correct 10° to 20° for every half mile. Without an RMI, use the CDI: re-center the needle with the OBS in steps ahead of you, turning to keep it centered (twist and turn). Leaving the arc, always lead the turn onto the radial: use the charted lead radial if there is one, or make your own, typically less than 5° for GA airplanes at 150 knots or less.

IPH (FAA-H-8083-16B), Departures; IFH (FAA-H-8083-15B), Navigation Systems

Brings together: Intercepting and Tracking Navigational Systems and DME Arcs · Departure, En Route, and Arrival Operations

Teaching this? The instructor lesson plan →

Study aid, not FAA guidance. Sources: Instrument Flying Handbook (FAA-H-8083-15B); Instrument Procedures Handbook (FAA-H-8083-16B); Aeronautical Information Manual (AIM); Instrument Rating ACS (FAA-S-ACS-8C). Checked against current sources 2026-11-13.