ACS Task IR.VI.B — Precision Approach (ILS, LPV)

What is ACS Task IR.VI.B?

ACS Task IR.VI.B is the precision approach task within Area of Operation VI (Instrument Approach Procedures) of the FAA Instrument Rating Airman Certification Standards (FAA-S-ACS-8C) . It evaluates a candidate's ability to fly a full ILS or LPV approach from the initial approach fix through DA, including configuration changes, navigation tracking, and the continue-or-miss decision.

The DPE will assign either an ILS or an LPV approach — or both — during the flight portion. You will brief the approach before beginning it and then fly it under simulated or actual instrument conditions. The evaluation continues through DA and into either the landing or the missed approach, which feeds directly into ACS Task IR.VI.C.

What are the components of an ILS approach?

An ILS approach has four main components, as described in AIM section 1-1-9 : the localizer, the glide slope, marker beacons or DME-based fixes, and approach lights. Understanding each component is required knowledge under IR.VI.B.

Localizer provides lateral course guidance centered on the runway extended centerline. The localizer is approximately 4 times more sensitive than a VOR — a full-scale deflection represents roughly ±2.5° at the runway threshold compared to ±10° for a VOR. This narrowing of the course width as you approach the runway is what makes precision tracking essential; small control inputs produce proportionally larger CDI movement close in.

Glide slope provides vertical guidance at a published angle, typically 3°, from the glide slope antenna located approximately 1,000 feet from the runway threshold. The glide slope intercept altitude is published on the approach chart and marks where you should begin your final descent. Full-scale glide slope deflection equals approximately ±0.7°.

Marker beacons and DME fixes identify position along the final approach course. The outer marker (OM), where installed, marks the glide slope intercept point. Many modern ILS approaches replace or supplement marker beacons with DME-based fixes or GPS position information. The middle marker (MM) is located near the Cat I decision height point. Inner markers are used only on Cat II and Cat III approaches.

Approach lights extend from the runway threshold outward, providing the visual transition from instrument to visual flight. They are the most commonly cited visual reference for continuing below DA under 14 CFR 91.175(c) , but approach lights alone only authorize descent to 100 feet above the TDZE.

How do LPV approaches differ from ILS approaches?

LPV (Localizer Performance with Vertical Guidance) approaches use the Wide Area Augmentation System (WAAS) to provide lateral and vertical approach guidance without ground-based transmitters. The Instrument Procedures Handbook (FAA-H-8083-16B) classifies LPV as an Approach with Vertical Guidance (APV) — it provides precision-equivalent accuracy but does not meet the ICAO definition of a precision approach.

For ACS checkride purposes, the FAA evaluates LPV approaches under Task IR.VI.B alongside ILS. Both use a DA rather than an MDA. LPV minimums can be as low as 200 feet and ½ statute mile — equal to Cat I ILS — at qualifying airports with sufficient WAAS signal geometry.

Key differences from ILS:

• Equipment requirement: LPV requires a WAAS-enabled GPS receiver approved for LPV operations (typically TSO-C146). A non-WAAS GPS can fly LNAV but not LPV.
• No physical glide slope antenna: Vertical guidance is computed by the avionics from WAAS corrections. The CDI still shows angular deviation, but the signal source is satellite-based.
• Course sensitivity scales like an ILS: Lateral deviation narrows as you approach the runway, which means the same tracking discipline required for ILS applies to LPV.
• RAIM vs. WAAS integrity: LPV approaches use WAAS integrity monitoring rather than receiver-autonomous integrity monitoring (RAIM). If WAAS is unavailable, the approach downgrades to LNAV or becomes unavailable entirely.

What is the difference between DA and DH?

Decision Altitude (DA) is referenced to mean sea level (MSL) and is used for Cat I ILS and all LPV approaches. Decision Height (DH) is referenced to height above touchdown zone elevation (HAT) and is used for Cat II and Cat III ILS operations requiring a special authorization.

For the instrument rating checkride, you will almost always encounter DA — the published MSL altitude at which you must decide to continue or execute a missed approach. The Instrument Procedures Handbook notes that at DA you are at the decision point — you do not level off, pause, or continue descending while deciding. The missed approach must begin immediately if the required visual references are not established.

Cat II and III are out of scope for the instrument rating practical test. The DPE will not ask you to demonstrate Cat II/III operations, but you are expected to know the category structure and that special authorization is required.

What are the ACS skill tolerances for IR.VI.B?

The Instrument Rating ACS (FAA-S-ACS-8C) specifies the following tolerances for precision approach skill elements:

These tolerances apply throughout the approach from the FAF inbound. Momentary exceedances that you promptly correct are evaluated differently than sustained deviations — but the DPE expects you to catch and correct within one to two needle-width cycles. Allowing the glide slope to go full-scale while you reconfigure is a common failure point.

What does the DPE look for during IR.VI.B?

The DPE evaluates three broad areas during the precision approach task: approach briefing quality, flight path management, and the DA decision.

Approach briefing must occur before you begin the approach. The DPE expects you to state the approach type, runway, DA, minimum visibility, missed approach procedure, primary and backup navigation, and any applicable NOTAMs. A disorganized or incomplete briefing signals that you are not ready to manage the approach under workload.

Flight path management is evaluated from the FAF inbound. The DPE watches for: glide slope intercept from below (preferred) vs. from above; timely gear and flap configuration; power management that maintains the published speed; and crosswind correction that keeps the aircraft tracking the localizer center. Chasing needle oscillations — responding to every momentary CDI movement with a heading change — is a common error that produces overcorrection and deviation cycles rather than stabilized tracking.

DA decision is the most-evaluated single moment. At DA, you must state "DA" or "minimums," then either: identify the required visual references and continue, or initiate the missed approach. Continuing below DA without positive visual reference identification is an immediate failure under 14 CFR 91.175(c) .

What are the most common errors on precision approaches?

• Descending below DA without required visual references. This is the most consequential error — a regulatory violation and automatic checkride failure. Call DA at the altitude, not after you pass it.
• Glide slope intercept from above. Intercepting the glide slope from above places you below the protected obstacle surface for a portion of the final segment. Always intercept from below unless an approach procedure specifically depicts a procedure turn that places you above the GS.
• Chasing the glide slope. Over-responding to glide slope deviation creates a pilot-induced oscillation. Use power to control descent rate; use pitch to fine-tune. Small, timely corrections outperform large, late ones.
• Unstabilized approach inside the FAF. The Instrument Procedures Handbook defines a stabilized approach as on speed, on glidepath, in landing configuration, with normal power settings by 1,000 feet AGL in IMC. If you are not stabilized by that point, the correct decision is a missed approach.
• Localizer hypersensitivity close to the runway. Because localizer angular width narrows with proximity to the antenna, small crab-angle corrections near the threshold produce large CDI movement. Fly heading, not the needle.
• Incomplete or rushed approach briefing. A DA omitted from the briefing is a DA that does not get called at the right time. Brief every item, every approach.

What risk management elements does the DPE evaluate?

The ACS risk management elements for IR.VI.B require you to demonstrate awareness of:

1. 1
   Conditions requiring a missed approach. Know the specific visual reference requirements of 14 CFR 91.175(c) and be prepared to state them. The DPE may ask "what would you need to see to continue?" before you fly the approach.
2. 2
   Equipment or navigation source failures during the approach. What do you do if the glide slope fails inbound? (Check the approach chart — a LOC-only approach may be available; otherwise, execute the missed approach.) What if WAAS integrity is lost on an LPV? (The avionics will downgrade — know what the CDI annunciator means on your specific equipment.)
3. 3
   Weather deteriorating below minimums. If the field reports below-minimums weather before you reach the FAF, the correct decision is to execute the missed approach and divert. Continuing in the hope that conditions improve is not an acceptable risk management strategy.
4. 4
   Crew/PIC fatigue and task saturation. An unstabilized approach inside the FAF in IMC is a go-around scenario regardless of weather — the ACS requires you to recognize this. The DPE may set up a scenario where continuing is the wrong choice.

Frequently Asked Questions

Q: What is the ACS altitude tolerance for a precision approach?

The Instrument Rating ACS requires you to maintain the glide slope/glide path within ±½ scale deflection and altitude within ±100 feet of the approach profile. At DA you must execute the missed approach unless you have the required visual references listed in 14 CFR 91.175(c) .

Q: What localizer deviation is acceptable under ACS IR.VI.B?

The ACS specifies ±¾ scale deflection on the localizer course. A localizer is 4 times more sensitive than a VOR — full-scale deflection is typically ±2.5° at the runway threshold, so ¾ scale is roughly ±1.9°. The standard should be tighter in practice; ¾ scale is the outer limit, not the target.

Q: What is the difference between a DH and a DA?

Decision Height (DH) is referenced to height above touchdown zone elevation (HAT) and is used for Cat II and Cat III ILS operations. Decision Altitude (DA) is referenced to MSL and is used for Cat I ILS and LPV approaches. Both represent the point at which a missed approach must begin unless required visual references are established.

Q: Is an LPV approach considered a precision approach on the ACS checkride?

Yes. The FAA treats LPV approaches as precision-equivalent for ACS testing purposes because they provide vertical guidance and use a DA rather than an MDA. The Instrument Procedures Handbook (FAA-H-8083-16B) classifies LPV as an APV, and the ACS evaluates it under the same IR.VI.B task as ILS.

Q: What visual references are required before descending below DA?

Under 14 CFR 91.175(c) , you must have one of these in sight: approach lights, threshold, threshold markings, threshold lights, REIL, VASI/PAPI, the touchdown zone or its markings or lights, or the runway or runway markings or lights. Flight visibility must also meet or exceed the published minimum.

Q: What are Cat I ILS approach minimums?

CAT I ILS minimums are a Decision Height of 200 feet HAT and visibility of ½ statute mile (or RVR 2,400 feet, reduced to 1,800 feet with operative touchdown-zone and rollout RVR reporting). These values are published on the approach chart and apply to Part 91 general aviation operations.

Q: What happens if you go below DA without the required visual references?

Descending below DA without the required visual references is a regulatory violation under 14 CFR 91.175(c) and a checkride failure. The ACS explicitly requires you to execute the missed approach immediately at DA if the required references are not established.

Q: What WAAS equipment is required to fly an LPV approach?

You need a WAAS-capable GPS receiver approved for LPV operations, typically certified under TSO-C146 or a later revision. The AIM section 1-1-18 covers WAAS requirements. Standard IFR-approved GPS receivers without WAAS cannot fly LPV approaches — they are limited to LNAV or LNAV/VNAV at best.

Sources

• 14 CFR 91.175 — Takeoff and Landing Under IFR
• AIM 1-1-9 — Instrument Landing System (ILS)
• AIM 1-1-18 — Wide Area Augmentation System (WAAS)
• FAA Instrument Procedures Handbook (FAA-H-8083-16B), Chapter 4
• FAA Instrument Rating ACS (FAA-S-ACS-8C)

This article was researched from FAA primary sources (ACS, FAR/AIM, Instrument Procedures Handbook) with citations to current 14 CFR Part 91 by MockDPE. Last updated: May 2026. If you spot an inaccuracy, email corrections@mockdpe.org.