Recognizing instrument failures

Start with the flight condition you should observe

Failure recognition starts with knowing normal indications. After a control or power change, compare the expected attitude and performance with what the instruments show. A gradual trend, a frozen value, an implausible jump, missing information or a failure annunciation can identify a problem. A discrepancy does not automatically identify which instrument is wrong.

For a normal coordinated turn, bank, turn rate and heading change should have a sensible relationship. For a climb, attitude and power must be consistent with airspeed and increasing altitude; a conventional VSI may lag before settling. An altimeter setting change or alternate-static selection can change indications without matching aircraft motion. Consider those known normal effects before assigning a fault.

Avoid fixation: staring at the instrument that looks wrong while aircraft control drifts. Expand the relevant cross-check, maintain control with corroborated information and reduce competing tasks. Do not make a large control change merely to satisfy one conflicting indication or a bodily sensation.

IFH 11-7: analog instrument failure · IFH 6-10–6-12: cross-check, interpretation and errors

Compare relevant evidence, not votes

Ask what each indication measures and which sources it shares. A display can be electrically separate but use the same sensor, or have a separate attitude sensor but share the main electrical supply. A standby airspeed indicator may be independent of the ADC yet share the blocked pitot/static plumbing. Independence must be evaluated for the particular suspected failure.

Use a combination that is relevant to the disagreement. A verified independent attitude reference is direct attitude evidence. Turn-rate and heading trends help assess bank/turn; airspeed, altitude and vertical-speed trends help assess pitch/performance. None of those individually supplies every piece of missing attitude information. GPS track and groundspeed add context but do not equal magnetic heading or indicated airspeed.

Do not use a majority vote from three indications supplied by one failed source. Conversely, the odd-one-out display is not necessarily wrong merely because two others agree. Combine the system map, source status, expected response and corroborating trends. If evidence remains inconclusive, treat the disputed data as suspect and use the aircraft's unreliable-data or failure guidance.

IFH 5-22–5-23: AHRS and ADC · IFH 11-7–11-8: cross-check during failure

Recognize patterns that suggest a common source

The following are clues for source reasoning, not final diagnoses or switch instructions. Partial blockages, intermittent wiring and processing faults may produce different combinations. Verify the actual installation and preserve aircraft control while checking the evidence.

Do not assume the engine has stopped because a charging alert appears. A conventional magneto-ignition engine may keep running after electrical-system loss, while an electrically dependent installation has different consequences. Likewise, a moving horizon does not prove adequate power, and a working radio does not prove a healthy alternator.

An AFCS or flight director using a suspect source may produce erroneous commands. Its apparent ability to hold something is not independent validation. Determine whether its sensors remain reliable and apply its published malfunction or disconnect guidance.

IFH 11-5–11-8: charging, analog, pneumatic and pitot/static failures · IFH 5-25–5-26: autopilot sensor dependencies

Inaccurate information may still look alive

An inoperative instrument may be blank, have an explicit failure flag, or no longer supply usable information. An inaccurate instrument may continue showing plausible numbers or a moving horizon. Both can be unsafe to use for the affected task. A self-test or an unflagged display does not prove that every supporting input is correct.

Know the meaning of the installed flags and messages. A red cross, off flag, source-disagreement message, invalid-data label or mode loss can apply to particular information rather than the entire display. Read the text and affected area, then follow the applicable procedure. Annunciations and colors are installation-specific; this lesson does not define one universal failure symbol.

When a navigation indication becomes unreliable, verify the selected source, signal/position status and active leg before attributing everything to a screen. GPS/GNSS disruption can affect position information even when a map remains visually plausible. Comparing two maps fed by the same navigator supplies no independent position confirmation. Use available independent navigation evidence and advise ATC if the equipment loss affects compliance; detailed navigation alternatives follow in later lessons.

Do not “clear” a warning by dismissing it and assume the underlying condition has gone away. Record what it said and reassess the source and aircraft response. A returning display after a reset still requires the checks and limitations prescribed by its manufacturer.

IFH 11-7: inaccurate and inoperative instrument recognition · AIM 1-1-13: user reports requested on NAVAID or GPS performance/anomalies

Keep control while reducing the task load

When a discrepancy appears, first preserve aircraft control using the reliable references you have identified. Continue the cross-check and keep airspeed, altitude and direction under observation. Do not let diagnosing the exact component take priority over a stable flight condition. If a real upset has developed, use the aircraft and instructor-taught recovery procedures; this is not a recovery tutorial.

1. ControlUse corroborated information and check the resulting performance.
2. SimplifyReduce programming and other competing tasks; assess suspect automation.
3. Use the checklistApply the appropriate published procedure and communicate needed assistance.

Identify the information or source that appears unreliable, then use the appropriate checklist as workload permits. Use an installed standby or approved alternate according to its procedure and limitations. A familiar label or a separate screen is not enough: verify its data and power. If erroneous automation is contributing to the problem, act under its malfunction/disconnect procedure while maintaining control.

Do not attempt continued IFR operation merely because some equipment remains illuminated. Reassess the available control and navigation capability, weather, terrain and workload with the aircraft procedures. Tell ATC when equipment trouble affects clearance compliance and request the assistance needed. The later partial-panel lesson develops reduced-instrument control and approaches; the emergency-decisions lesson develops diversion and landing choices.

IFH 11-7–11-8: maintaining control, checklists and ATC · ACS VII.D: recognition, control and distraction risks

Restoring power is not automatically a safe fix

Use the applicable AFM/POH and approved supplements for alternate-static selection, standby activation, display reversion, source switching and electrical load management. Do not import another aircraft's sequence, promised battery endurance or bus assignment. A source switch can introduce different errors or remove other capabilities, so check the resulting indications and remaining information.

Do not pull or reset circuit breakers as a general troubleshooting routine. Circuit protection may be responding to a genuine electrical fault; reenergizing it can produce heat or fire. Follow explicit approved procedures and their restrictions, and do not repeatedly reset a tripping breaker. Smoke, burning odor or unusual heat requires the applicable smoke/fire response rather than an improvised attempt to restore a display.

In ground preparation, locate the relevant checklists and have an instructor explain the allowed fault-isolation actions. Practice failures with appropriate instructor-directed simulation rather than disabling live aircraft systems casually. Write down the first warning, affected data and response to any authorized action so that repeated resets or screen changes do not erase the evidence.

Common error: assuming that bringing a display back proves the fault is repaired or that an alternate source is now error-free. A restored indication is usable only within the manufacturer's checks, validity indications and operating limitations.

IFH 11-4–11-8: display, power and alternate sources · FAA SAIB CE-10-11: fire hazard and approved-procedure cautions for circuit breakers · Current FAA Glider Flying Handbook 8-23: circuit-breaker fire caution, citing CE-10-11R1

Describe the effect and preserve a useful record

As workload permits, advise ATC of the equipment problem and what it prevents you from doing. “Primary attitude indication unreliable; using standby; unable assigned turn for now” communicates more useful information than a speculative component diagnosis. State the actual situation and request appropriate assistance; do not wait for certainty about a circuit board before reporting a capability loss.

A source failure can also affect altitude reporting, navigation or communications through shared power or data. If ATC reports an altitude discrepancy, check the altimeter setting, source dependencies and applicable procedure rather than changing altitude merely to make a reported number match. Explain the observed discrepancy and preserve safe control using reliable information.

After flight, record the warning text, phase of flight, conditions, values/trends, equipment affected and checklist actions. A report such as “heading display stuck at 210° during taxi, source message displayed, persisted after prescribed check” is more useful than “avionics bad.” Maintenance and required airworthiness decisions must be resolved before subsequent operation under the applicable requirements.

For this lesson, success means explaining which evidence is reliable and what initial priorities follow. It does not establish the skill to fly a partial-panel approach or make every emergency landing decision. Those require later ground study and instructor-led flight practice.

ACS VII.D.K1/K2 and R1/R2/R3: recognition, ATC, secondary displays and priorities · IFH 11-7–11-8: communication and system failure

FLIGHT SCENARIO

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