ACS Task IR.V.A — Intercepting and Tracking Nav Systems + DME Arcs

What does ACS Task IR.V.A cover?

IR.V.A is the ACS task that tests every core en-route navigation skill: intercepting a VOR radial or GPS course, bracketing for wind correction, flying a DME arc, and transitioning from an arc to an inbound approach course. It sits in Area V (Navigation Systems) of the Instrument Rating ACS (FAA-S-ACS-8C) alongside IR.V.B (Departure, En Route, and Arrival Operations).

The DPE evaluates three categories of elements in this task:

What VOR knowledge does the DPE expect?

A VOR CDI represents ±10° of course deviation at full-scale deflection, per AIM Section 1-1-3. Each dot on the CDI is typically 2°. A ±3/4-scale deflection therefore represents approximately 7.5° of course error — the maximum the ACS tolerates.

The DPE will expect you to explain the TO/FROM ambiguity zone and the cone of silence directly overhead the station. Near the station, CDI sensitivity increases because the angular difference between the course and your position changes rapidly with small horizontal displacements. FAA-H-8083-15B Chapter 9 recommends crossing directly over the station or using a time reference rather than trying to track a VOR course within a few miles of the transmitter.

The VOR receiver in your aircraft must have a current equipment check per 14 CFR 91.171 — within 30 days if using a VOT, airborne check, or dual-VOR check. The DPE may ask you to produce the logbook entry.

How do you intercept and track a VOR course?

Intercepting a VOR radial uses a 3-step procedure: identify the station, set the OBS to the desired course, then turn to an intercept heading. FAA-H-8083-15B Chapter 9 describes a standard intercept as 30–45° offset from the desired course heading, reducing to a wind-correction heading as the CDI centers.

Once established on course, use the bracketing technique:

1. 1
   Fly the course heading and note which direction the CDI deflects over time — this indicates the wind correction needed.
2. 2
   Apply a wind correction angle (WCA) by turning 10–20° into the wind. Hold the new heading for 1–2 minutes.
3. 3
   If the CDI moves back toward center, the correction is working. If it continues to deflect, increase the WCA.
4. 4
   Halve the correction angle once the CDI returns to center and hold — this is your bracketing increment.
5. 5
   Repeat in smaller steps until the CDI remains stationary. That heading is your wind-corrected course.

What does the DPE look for in GPS/RNAV tracking?

GPS/RNAV displays cross-track error (XTE) on the CDI just as a VOR does, but the scale is distance-based, not angular. En route, full-scale deflection is typically 5 nm; in terminal mode it transitions to 1 nm; on approach, it reduces to 0.3 nm. AIM Section 1-1-17 describes RNAV and WAAS signal standards.

How is ILS localizer sensitivity different from VOR?

An ILS localizer is approximately 4 times more sensitive than a VOR CDI at the same deflection reading. A VOR at full-scale represents ±10°; an ILS localizer at full-scale represents roughly ±2.5° (the exact value varies by localizer antenna design, but the FAA Instrument Flying Handbook states the localizer is approximately 4 times more sensitive than a VOR). This is documented in FAA-H-8083-15B Chapter 9.

The practical implication: a quarter-dot deflection on a localizer represents a much smaller course error than on a VOR. Pilots transitioning from VOR tracking to ILS must reduce their control inputs proportionally. The ±3/4-scale CDI standard in the ACS still applies, but on a localizer that tolerance is significantly tighter in linear terms as you approach the runway threshold.

How do you fly a DME arc?

A DME arc is a curved flight path at a constant DME distance from a VOR/DME station. FAA-H-8083-15B Chapter 9 describes the standard technique: because it is impractical to fly a perfect curve, pilots approximate the arc by flying a series of short chord legs using the "turn 10°" method.

1. 1
   Intercept the arc: track inbound on a radial to the arc distance, then turn 90° in the direction of the arc (toward the approach course).
2. 2
   Establish the perpendicular heading: once on the arc distance, your heading should be approximately 90° offset from the bearing TO the station.
3. 3
   Monitor DME: as you fly each chord, the DME will increase slightly (you are cutting inside the arc). When the DME reads more than 0.5 nm above the arc radius, turn 10° toward the station.
4. 4
   Roll back when the needle centers: as your new heading brings you back toward the arc, the CDI (set to a radial you are crossing) or the DME will return to the arc value. Roll back to the perpendicular heading.
5. 5
   Repeat every 30–60 seconds: the result is a series of chord legs that closely approximate the arc. Normal training aircraft at typical arc speeds produce legs of roughly 1–2 nm.
6. 6
   Lead the final radial: identify the lead radial — typically 5–10° before the final approach course — and turn inbound to roll out on the published course.

The lead radial compensates for the turn radius at your groundspeed. At slower training aircraft speeds (90–100 knots), 5° of lead is usually sufficient. At higher speeds or with a strong tailwind component, more lead is needed. FAA-H-8083-15B Chapter 9 provides the lead-radial calculation method.

What are the ACS Skill tolerances for IR.V.A?

The Instrument Rating ACS (FAA-S-ACS-8C) Appendix specifies these in-flight standards for all navigation tasks:

What does the DPE look for during IR.V.A?

The DPE evaluates whether you maintain a systematic, proactive approach to navigation — not reactive chasing of the needle. Common patterns that DPEs report as satisfactory include: applying a correction before the CDI deflects fully, verifying nav identification (Morse code or name) before relying on the indication, and communicating any nav abnormality (e.g., RAIM alert, flagged VOR) promptly.

The DPE may demonstrate a wind component by assigning a course with a significant crosswind and observing whether you recognize the drift, apply a correction, and bracket to a stable wind-corrected heading — or whether you repeatedly over-correct and let the CDI wander.

For the DME arc, the DPE looks for: smooth entry from the intercept radial, consistent use of the 10° chord technique, and a timely, coordinated turn at the lead radial that results in rolling out on the final approach course within the CDI tolerance.

What are the most common errors on IR.V.A?

• Chasing the needle: making large, impulsive heading corrections in response to CDI deflection rather than using the bracketing method to find a stable wind correction angle.
• Ignoring nav ID: flying an unidentified VOR or ILS localizer. The FAA Instrument Flying Handbook and AIM both require positive identification before relying on a navigation signal.
• Over-banking on the DME arc: using more than standard-rate turns on the chord adjustments, which causes the arc to oscillate between inside and outside the published radius.
• Late lead radial turn: rolling out past the final approach course, requiring a corrective S-turn that unsettles both CDI and altitude.
• ILS sensitivity surprise: applying the same correction amplitude used on VOR tracking when flying a localizer, resulting in an overshoot because the localizer is approximately 4× more sensitive.
• Failing to cross-check altitude: fixating on the CDI while altitude drifts outside the ±100-foot tolerance.

Frequently Asked Questions

Q: What CDI deflection tolerance does the ACS allow on IR.V.A?

The Instrument Rating ACS specifies ±3/4-scale CDI deflection for intercepting and tracking navigational courses. Exceeding this limit — even briefly — constitutes an unsatisfactory Skill element. During a DME arc the same standard applies: the CDI should remain within 3/4 scale of the arc centerline.

Q: How is an ILS localizer more sensitive than a VOR?

A VOR CDI represents ±10° full-scale deflection (centered on the selected radial). An ILS localizer CDI represents approximately ±2.5° full-scale — roughly 4 times more sensitive — because the localizer beam is narrower near the runway. FAA-H-8083-15B Chapter 9 describes this sensitivity difference explicitly.

Q: What is the "turn 10°, roll back when needle centers" technique for a DME arc?

This is the FAA-canonical DME arc tracking method described in FAA-H-8083-15B. Turn 10° toward the station when the DME reading increases above the arc radius, then roll back to a heading perpendicular to the station bearing when the CDI/DMI centers. This produces a series of short chord legs that closely approximate the arc.

Q: What lead radial should I use to turn inbound from a DME arc?

The lead radial is the VOR radial you cross before the final approach course radial, used to begin the inbound turn early enough so the aircraft rolls out on course. The exact lead radial depends on groundspeed and bank angle. FAA-H-8083-15B Chapter 9 provides the guidance; most instrument training uses 5–10° of lead for typical training aircraft speeds.

Q: Does IR.V.A apply to GPS-only aircraft that have no VOR receiver?

Yes. The ACS requires demonstration of intercepting and tracking "navigational systems," which includes GPS/RNAV. The DPE evaluates your ability to intercept and maintain a GPS course within ±3/4-scale CDI regardless of the nav source. VOR-specific tasks apply only when the aircraft is equipped with a VOR receiver.

Q: What does "bracketing" mean in the context of VOR tracking?

Bracketing is the systematic technique for finding a wind correction angle: apply a correction, note whether the needle moves toward or away from center, then adjust in smaller and smaller increments until the CDI stabilizes. FAA-H-8083-15B Chapter 9 describes bracketing as the standard method for identifying the wind correction angle on a VOR course.

Q: What is the difference between a TO and FROM indication on a VOR?

A TO flag means the selected radial (OBS setting) will take you toward the station if you fly the indicated heading. A FROM flag means you are tracking away from the station on that radial. Ambiguity zone near the station boundary can produce unreliable indications — AIM Section 1-1-3 addresses VOR signal characteristics and cone of silence.

Q: What ACS Skill elements are tested in flight for IR.V.A?

The ACS Skill elements require you to: intercept a navigational course within ±3/4-scale CDI; track the course maintaining ±3/4-scale deflection; maintain altitude ±100 feet; maintain heading ±10 degrees when applicable; and, if a DME arc is assigned, fly the arc within the same CDI tolerance. All elements must be met simultaneously per FAA-S-ACS-8C Change 1.

Sources

• FAA Instrument Rating ACS (FAA-S-ACS-8C Change 1)
• FAA Instrument Flying Handbook (FAA-H-8083-15B), Chapter 9 — Navigation Systems
• FAA Instrument Procedures Handbook (FAA-H-8083-16B)
• AIM Section 1-1 — Navigation Aids (VOR, ILS, GPS/RNAV)
• 14 CFR 91.171 — VOR Equipment Check for IFR Operations

This article was researched from FAA primary sources (ACS, FAA-H-8083-15B, AIM, 14 CFR Part 91) by MockDPE. Last updated: May 2026. If you spot an inaccuracy, email corrections@mockdpe.org.