ACS Task IR.VII.C — Approach with Loss of Primary Flight Instrument Indicators

What does ACS Task IR.VII.C require you to demonstrate?

IR.VII.C tests your ability to recognize a primary flight instrument failure, transition your scan to remaining instruments, and complete an approach to published minimums — all without your normal attitude and heading references. The FAA Instrument Rating ACS (FAA-S-ACS-8C) places this task in Area VII (Emergency Operations), which signals the DPE's expectations: this is not a routine procedure, and your response to the failure matters as much as your flying technique.

The DPE will typically simulate the failure by covering the AI and HI (analog cockpit) or by selecting reversion on a glass cockpit during the approach sequence. Your job is to recognize the failure, verbalize what happened, restructure your scan, and complete the approach using the remaining instruments without exceeding the wider ACS tolerances.

What instruments fail during a vacuum system failure — and why?

In an analog cockpit, a vacuum system failure causes the loss of the attitude indicator (AI) and the directional gyro/heading indicator (HI). Both are gyroscopic instruments that depend on suction from the vacuum pump to spin their gyros. When vacuum pressure drops, the gyros gradually tumble or precess, and their indications become unreliable.

The FAA Instrument Flying Handbook (FAA-H-8083-15B), Chapter 5, explains that gyroscopic instruments in light aircraft use either vacuum (suction) or electrical power as their energy source. The key split is:

A vacuum failure is insidious because the instruments do not immediately go to an extreme position — they degrade gradually over 2–3 minutes as gyro RPM drops. The AI may show a slight but believable bank before becoming unreliable. This is why recognizing instrument failure quickly, rather than chasing a slowly erring instrument, is a core ACS knowledge element.

What is the correct partial panel scan for an analog approach?

After identifying a vacuum failure, shift your instrument cross-check to the four remaining pitot-static and electrical instruments per FAA-H-8083-15B Chapter 7. Your scan hierarchy on partial panel becomes:

1. 1
   Turn coordinator — primary bank reference; a standard-rate turn shows the wing aligned with the lower index mark.
2. 2
   Altimeter — primary altitude reference; trend and rate of change are your first warnings of pitch divergence.
3. 3
   Airspeed indicator — confirms pitch attitude indirectly; increasing airspeed signals a nose-low pitch trend.
4. 4
   Vertical speed indicator (VSI) — supports altitude control; treat as a trend instrument, not an exact rate.
5. 5
   Magnetic compass — primary heading reference, used only in straight, coordinated, unaccelerated flight.
6. 6
   Inclinometer (ball) — still valid; keep the ball centered at all times to ensure coordinated flight.

Control workload is higher on partial panel because you no longer have a direct attitude reference. Use small, deliberate control inputs. Trim aggressively to reduce stick-and-rudder workload. Any significant pitch or bank change must be confirmed across multiple instruments before further correction.

What are the magnetic compass errors you must know for partial panel?

The magnetic compass becomes your only heading reference on partial panel, but it introduces two categories of error that DPEs specifically test per FAA-H-8083-15B Chapter 5.

Acceleration errors — ANDS:

| Heading | Acceleration | Compass Indicates | |---------|-------------|-------------------| | East or West | Accelerate | Swing toward North | | East or West | Decelerate | Swing toward South |

The mnemonic is ANDS: Accelerate North, Decelerate South. Errors are greatest on east and west headings and zero on north and south headings.

Northerly turning errors — UNOS:

| Turn Direction | Correction | |----------------|-----------| | Turning TO north | Undershoot — roll out early by approximately your latitude in degrees | | Turning TO south | Overshoot — roll out late by approximately your latitude in degrees |

The mnemonic is UNOS: Undershoot North, Overshoot South. These errors result from the compass card's pendulous vanes dipping toward the Earth's magnetic field at northerly and southerly headings. Errors are greatest at the poles and zero at the magnetic equator. At a latitude of 40° N (central United States), plan to lead or lag by approximately 40°.

To use the compass accurately: read it only during straight, unaccelerated, coordinated flight. Allow oscillations to dampen before accepting the reading. Apply the correction card in the cockpit for compass deviation (swinging error from aircraft electrical fields).

How does partial panel work in a glass cockpit (PFD failure)?

Glass cockpit partial panel is structurally different from analog but tests the same underlying skill: maintaining control and completing an approach without your primary attitude display. Per the FAA Instrument Flying Handbook (FAA-H-8083-15B) Chapter 7, modern EFIS-equipped aircraft provide three layers of redundancy:

The DPE may simulate a glass cockpit partial panel by covering the PFD with a suction-cup cover or by having you close your eyes while they select reversionary mode. In either case, your first action is to identify which instruments are valid, verbalize the failure, and restructure your scan around the remaining displays — including the standby instrument if required.

What are the ACS tolerances for a partial panel approach?

The FAA Instrument Rating ACS (FAA-S-ACS-8C) specifies wider tolerances for partial panel operations than for full-panel approaches, reflecting the increased workload. The examiner expects:

Altitude and airspeed tolerances are identical between full and partial panel. The meaningful difference is the heading tolerance doubling from ±5° to ±10°, which reflects the difficulty of maintaining precise track without a gyroscopic heading reference. Despite the wider tolerance, the DPE still expects deliberate, purposeful flying — wandering randomly within the tolerance band is not acceptable.

What does the DPE look for in IR.VII.C?

The DPE is evaluating four things simultaneously during a partial panel approach:

Recognition: Did you correctly identify the failed instruments and name the system (vacuum) that failed? Vague answers like "the attitude indicator seems off" are not sufficient. The examiner expects: "The vacuum system has failed — my AI and HI are unreliable. I'm transitioning to partial panel using the turn coordinator, altimeter, airspeed, and magnetic compass."

Restructured scan: Does your eye movement reflect the new hierarchy? On full panel, the AI is the hub of the control scan. On partial panel, the turn coordinator and altimeter share that role. The DPE watches your eyes and control inputs to assess whether your scan is organized or reactive.

Compass discipline: Do you read the compass only in straight, unaccelerated flight? Do you apply ANDS and UNOS corrections appropriately when maneuvering? The DPE often asks verbal questions about compass errors during the approach to confirm your knowledge while you fly.

Approach completion: Do you arrive at DA or MDA in a position to land? The approach must be flown to published minimums — a partial panel failure is not grounds to abandon the approach unless you determine that doing so is the safer option, in which case you should verbalize a missed approach and execute it precisely.

Risk Management elements in IR.VII.C

The ACS identifies several risk management areas specific to this task:

Early failure recognition: The greatest risk in a vacuum failure is not recognizing it. A slowly precessing AI can mislead you into an unusual attitude before the failure is obvious. Per FAA-H-8083-15B, the correct cross-check habit is to periodically verify gyroscopic instruments against the pitot-static and electrical backup instruments, even in normal IMC. Discrepancies between the AI bank indication and the turn coordinator are the most common early failure signature.

Task saturation: Flying an approach on partial panel is a high-workload event. The DPE expects you to demonstrate workload management — prioritize control of the aircraft first (aviate), maintain situational awareness about your approach progress (navigate), and manage radio communication as workload permits (communicate). Declaring an emergency with ATC for additional support is appropriate and professionally sound.

Decision to continue or miss: If the partial panel approach becomes uncontrollable or you cannot maintain approach tolerances, executing the missed approach and landing VFR or diverting to VMC is the correct decision. The ACS does not require you to fly to minimums if doing so creates an unsafe condition.

Common Errors in IR.VII.C

• Continuing to cross-check the failed AI or HI rather than excluding them from the scan — failed instruments must be mentally eliminated, not periodically rechecked.
• Reading the magnetic compass during a turn or immediately after a pitch/bank change — compass must be read only in straight, unaccelerated, coordinated flight.
• Forgetting ANDS corrections during speed changes on approach, especially on deceleration from cruise to approach speed.
• Applying UNOS lead/lag in the wrong direction — undershoot (roll out early) for northerly headings, overshoot (roll out late) for southerly headings.
• Over-controlling due to absence of direct attitude reference — use small, deliberate inputs and rely on trim to reduce workload.
• Failing to verbalize the failure and restructured scan to the DPE — silence during a failure scenario signals confusion rather than competence.
• Confusing the turn coordinator bank index with a specific bank angle — the lower index represents standard-rate (3°/sec), not a fixed bank angle.
• Not knowing the location and operation of the standby attitude indicator or ESI before the flight (glass cockpit applicants).

Practice Questions

Frequently Asked Questions

Sources

• FAA Instrument Flying Handbook (FAA-H-8083-15B) — Chapter 5 (Flight Instruments) and Chapter 7 (Attitude Instrument Flying)
• FAA Instrument Rating ACS (FAA-S-ACS-8C)
• FAA Instrument Procedures Handbook (FAA-H-8083-16B)
• Aeronautical Information Manual (AIM), Chapter 1 — Air Navigation

This article was researched from FAA primary sources (FAA-H-8083-15B Chapters 5 and 7, FAA Instrument Rating ACS FAA-S-ACS-8C, FAA-H-8083-16B) by MockDPE. Last updated: May 2026. If you spot an inaccuracy, email corrections@mockdpe.org.