ACS Task IR.VII.B — One Engine Inoperative (Multi-Engine IFR)

What does ACS Task IR.VII.B cover, and who must demonstrate it?

IR.VII.B is the only task in the Instrument Rating ACS that is explicitly designated "Multi-Engine Only" by the FAA Instrument Rating ACS (FAA-S-ACS-8C). Single-engine applicants skip this task entirely. If you are testing in a multi-engine airplane, the DPE will evaluate your ability to continue an IFR approach and execute a missed approach with one engine inoperative — one of the highest-workload scenarios in instrument flying.

The task is organized under Area VII — Emergency Operations — because an engine failure during an IFR approach is precisely the scenario where poor prioritization or inadequate preparation costs lives. The DPE evaluates all three ACS elements: Knowledge, Risk Management, and Skills.

What V-speeds must I know for OEI IFR operations?

The three V-speeds that govern single-engine operations are aircraft-specific. Do not memorize generic numbers — consult your aircraft's POH/AFM for actual values. What the ACS requires you to know is the definition and operational significance of each:

According to FAA-H-8083-3C, Chapter 13, Vmc is published under a standardized set of conditions (maximum certified takeoff weight, critical engine windmilling, airplane in the most critical configuration, etc.) — and actual controllability in your aircraft under real conditions may vary. Fly the blue line (Vyse) on any OEI missed approach and you will always be on the correct side of the performance curve.

What is the drift-down concept and when does it apply?

Drift-down is a controlled descent to single-engine cruise altitude after an engine failure at high altitude where the remaining engine cannot maintain the current altitude. The procedure applies primarily to high-altitude multi-engine operations, but the ACS expects all multi-engine instrument candidates to understand the concept because the principle — controlled loss of altitude to find a performance-sustainable altitude — underlies any OEI scenario where level flight is not possible.

Per FAA-H-8083-3C, Chapter 13, during drift-down you configure the aircraft at the OEI best-range or minimum-drag speed per the AFM, secure the failed engine per the emergency checklist, and navigate toward the nearest suitable airport while descending to your single-engine service ceiling. The single-engine absolute ceiling (where the aircraft can no longer climb at all on one engine) and single-engine service ceiling (where climb rate drops to 50 ft/min) are published in your POH performance section.

The DPE may ask: "What would you do if you lost an engine at cruise altitude and the aircraft cannot hold altitude?" A complete answer covers drift-down speed, obstacle clearance awareness, fuel management, ATC declaration, and diversion planning.

What are asymmetric thrust effects and why do they matter on approach?

When one engine fails, the operating engine produces thrust offset from the aircraft centerline, creating a yawing moment toward the dead engine. The Airplane Flying Handbook Chapter 13 identifies the following effects the ACS expects you to explain:

• Yaw toward the inoperative engine — countered with rudder toward the operative engine.
• P-factor (asymmetric propeller disk loading) on the operative engine — increases the yawing tendency, especially at high angles of attack and low airspeed.
• Torque from the operative engine — rolls the aircraft toward the inoperative engine.
• Slipstream effect — reduced when one engine is feathered, altering airflow over the tail.
• Accelerated/spiraling slipstream on the operative side — can affect aileron effectiveness.

These forces combine to make an OEI airplane significantly more demanding to fly than the same airplane at full power. Maintaining coordinated flight — ball centered, wings level, Vyse — is the fundamental skill the DPE observes throughout the OEI scenario.

What are the ACS tolerances for an OEI instrument approach?

The FAA Instrument Rating ACS recognizes that OEI flight imposes substantial additional workload and permits wider tolerances than during normal two-engine IFR operations:

The wider altitude and airspeed tolerances reflect the real-world difficulty of managing an asymmetric aircraft, working checklists, and flying a precision or nonprecision approach simultaneously. However, the DPE still expects you to fly the approach as precisely as the OEI performance allows — the extra tolerance is not an invitation to be sloppy.

Risk Management: sterile cockpit and the emergency declaration decision

Two risk management elements receive particular examiner attention in IR.VII.B:

Sterile cockpit at MDA/DA. The sterile cockpit concept — derived from 14 CFR 121.542 for Part 121 carriers but adopted as best practice for all IFR operations — prohibits non-essential crew communication and activity during critical phases of flight. On an OEI approach, once you are inside the final approach fix and especially approaching MDA or DA, 100% of your attention belongs on flying the aircraft and monitoring the approach. The DPE will notice if you engage in non-essential conversation or checklist work at that point in the approach.

When to declare an emergency. Under 14 CFR 91.3(b), the PIC may deviate from any rule to the extent necessary to meet an emergency. The ACS expects you to know that declaring an emergency with ATC is the right call in any OEI approach situation where you are uncertain of the outcome. Declaration gives you priority handling, ARFF standby, and removes any regulatory burden from making the decision that saves the flight. There is no regulatory penalty for declaring an emergency that turns out not to require it. The cost of not declaring when you should have is potentially fatal.

Skill Elements: what you must actually do in the aircraft

The DPE evaluates your practical execution of the following sequence per the FAA Instrument Rating ACS:

1. 1
   Identify the inoperative engine — verify by reducing the operating engine's power momentarily if needed (confirm, don't assume).
2. 2
   Apply appropriate control inputs to maintain directional control — rudder toward the operative engine, wings level.
3. 3
   Announce the engine failure and initiate the POH emergency checklist — memory items first (maintain aircraft control, identify, verify, feather if appropriate), then checklist to confirm and complete.
4. 4
   Establish and maintain Vyse (blue-line airspeed) — this is your single most important performance parameter.
5. 5
   Continue or discontinue the approach per your briefed decision criteria and available single-engine performance.
6. 6
   If continuing: fly the approach to MDA or DA maintaining Vyse and OEI configuration. At MDA, apply the rules of 14 CFR 91.175(c) — do not descend below MDA unless you have the required flight visibility and runway environment in sight.
7. 7
   If executing the missed approach: apply full power to the operative engine, establish the OEI missed approach climb configuration per the POH (gear up, drag cleanup), maintain Vyse, and follow the published missed approach procedure.
8. 8
   Communicate with ATC — declare emergency if appropriate, advise intentions, request priority handling.

The sequence must come from your POH/AFM checklist, not from memory alone. The DPE is watching for checklist discipline, not a memorized recitation.

What the DPE Looks For

The DPE evaluating IR.VII.B watches for several non-obvious indicators of mastery:

1. Aircraft control first, always. Every evaluation point comes second to maintaining positive aircraft control. A candidate who reaches for the checklist while letting the aircraft deviate from heading and Vyse has failed the most important priority test.
2. "Identify before you feather." The classic training phrase reflects a real accident history. The DPE will listen for verbal confirmation that you identified and verified the failed engine before feathering. Feathering the wrong engine in IMC is not recoverable.
3. Approach briefing that accounts for OEI. Before the scenario, the DPE expects to hear a missed approach briefing that explicitly addresses OEI performance — not the standard two-engine missed approach procedure applied unchanged.
4. DA/MDA discipline. The rules of 14 CFR 91.175(c) still apply. An OEI emergency does not authorize descent below MDA without the required visual references.
5. Genuine use of the checklist. DPEs can tell the difference between a candidate who uses the checklist as a verification tool and one who performs the checklist as theater. Use it as a tool.

Common Errors in IR.VII.B

• Feathering the operating engine — the classic (and fatal) error. Always confirm before feathering: dead foot, dead engine.
• Letting airspeed decay below Vyse on the missed approach — loss of Vyse is the primary cause of OEI loss-of-control accidents.
• Treating an OEI missed approach identically to a normal missed approach — different power-to-weight ratio, different climb rate, different checklist sequence.
• Delaying checklist use — attempting to manage the emergency entirely from memory when the POH checklist is available and should be used.
• Non-sterile cockpit at DA/MDA — performing checklist items or non-essential communication at the most critical point of the approach.
• Failing to declare an emergency when performance is uncertain — the DPE will ask why you did not declare if the situation clearly warranted it.
• Not briefing OEI performance before the approach — missing the single-engine service ceiling, missed approach gradient, and whether the aircraft can execute the published missed approach on one engine.

Practice Questions

Frequently Asked Questions

Sources

• FAA Instrument Rating ACS (FAA-S-ACS-8C)
• FAA Airplane Flying Handbook (FAA-H-8083-3C), Chapter 13 — Transition to Multiengine Airplanes
• Aeronautical Information Manual (AIM), Chapter 6 — Emergency Procedures
• 14 CFR 91.3 — Responsibility and Authority of the Pilot in Command
• 14 CFR 91.175 — Takeoff and Landing Under IFR
• Aircraft Flight Manual / POH — aircraft-specific V-speed values (consult your aircraft's POH/AFM)

This article was researched from FAA primary sources (ACS FAA-S-ACS-8C, Airplane Flying Handbook FAA-H-8083-3C, AIM, 14 CFR Part 91) by MockDPE. V-speed values (Vmc, Vyse, Vsse) are aircraft-specific — consult your aircraft's POH/AFM for actual figures. Last updated: May 2026. If you spot an inaccuracy, email corrections@mockdpe.org.