2.2 Inoperative Equipment, MELs & 14 CFR 91.213

Inoperative Equipment, MELs & 14 CFR 91.213

During preflight inspection for an IFR flight, discovering inoperative equipment requires a systematic legal and aeronautical decision-making process. Flying with broken or malfunctioning equipment is strictly regulated under 14 CFR § 91.213.

As Pilot-in-Command (PIC), you must determine whether the aircraft can legally and safely depart with the inoperative item, whether it must be repaired or deferred, or whether a Special Flight Permit is required.

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1. The Two Regulatory Pathways of 14 CFR 91.213

When any instrument or item of equipment is discovered to be inoperative prior to takeoff, the pilot must determine which regulatory branch applies:

1. Operations with an Approved Minimum Equipment List (MEL) under 14 CFR 91.213(a): Primarily utilized by turbine aircraft, corporate flight departments, multi-engine aircraft, and commercial operators.
2. Operations Without an MEL under 14 CFR 91.213(d): The standard procedure for most Part 91 general aviation single-engine and light aircraft.

+-----------------------------------------------------------------------------+
|                     14 CFR 91.213 REGULATORY PATHWAYS                       |
|                                                                             |
|   [DISCREPANCY / INOPERATIVE ITEM DISCOVERED]                               |
|                        |                                                    |
|                        +---> Has FAA-Approved MEL? (91.213(a))              |
|                        |     ---> Follow Tail-Specific MEL & LOA            |
|                        |                                                    |
|                        +---> No MEL? (91.213(d))                            |
|                              ---> Apply 4-Step Regulatory Filter:           |
|                                   1. VFR-Day Type Certificate (TCDS)        |
|                                   2. Kinds of Operations List (KOEL)        |
|                                   3. 14 CFR 91.205 / 91.207 / 91.215        |
|                                   4. Airworthiness Directives (ADs)         |
+-----------------------------------------------------------------------------+

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2. Operations with an Approved MEL (14 CFR 91.213(a))

An Approved Minimum Equipment List (MEL) is a legally binding, FAA-approved document tailored specifically to an individual aircraft make, model, and registration/serial number.

MMEL vs. Operator MEL

• Master Minimum Equipment List (MMEL): Created by the FAA's Flight Operations Evaluation Board (FOEB) in conjunction with aircraft manufacturers for an entire aircraft type (e.g., all Cessna 172S aircraft). An MMEL cannot be used directly by a pilot for flight operations.
• Operator's MEL: Developed by the aircraft owner/operator from the MMEL, submitted to the local FAA Flight Standards District Office (FSDO), and approved along with an official Letter of Authorization (LOA). Once the LOA is issued, the MEL becomes a Supplemental Type Certificate (STC) governing that specific tail number.

MEL Relief Categories

MEL deferrals are categorized by repair interval urgency:

• Category A: Specified time interval listed in the "Remarks or Exceptions" column (e.g., flight cycles, flight hours, or days).
• Category B: Must be repaired within 3 consecutive calendar days (72 hours).
• Category C: Must be repaired within 10 consecutive calendar days (240 hours).
• Category D: Must be repaired within 120 consecutive calendar days.

(M) and (O) Procedures

• (M) Maintenance Procedure: Requires an authorized maintenance technician (A&P mechanic) to calibrate, lock out, disconnect, or safety the component before flight.
• (O) Operational Procedure: Specific operational technique or restriction executed by the flight crew/pilot (e.g., remaining outside icing conditions, computing manual climb gradients).

[!IMPORTANT] MEL Binding Effect: If an aircraft has an approved MEL with an LOA, the pilot cannot choose to operate under 14 CFR 91.213(d). The MEL is mandatory. If an inoperative item is not listed in the MEL, and no relief is provided, the aircraft is grounded until the item is repaired.

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3. Operations Without an MEL: The 4-Step Filter (14 CFR 91.213(d))

For general aviation aircraft operating without an MEL, 14 CFR § 91.213(d) establishes a rigorous four-step airworthiness elimination filter. The pilot must evaluate whether the inoperative equipment is required by any of the following four sources:

+-----------------------------------------------------------------------------+
|               14 CFR 91.213(d) FOUR-STEP AIRWORTHINESS FILTER               |
|                                                                             |
|   [STEP 1] Part of VFR-Day Type Certification (TCDS / CAR 3 / Part 23)?     |
|            NO  |   YES ---> [AIRCRAFT GROUNDED]                             |
|            v                                                                |
|   [STEP 2] Listed as Required on KOEL / Comprehensive Equipment List?       |
|            NO  |   YES ---> [AIRCRAFT GROUNDED]                             |
|            v                                                                |
|   [STEP 3] Required by 14 CFR 91.205 (b, c, d), 91.207, or Part 91?         |
|            NO  |   YES ---> [AIRCRAFT GROUNDED]                             |
|            v                                                                |
|   [STEP 4] Mandated by any Airworthiness Directive (AD)?                    |
|            NO  |   YES ---> [AIRCRAFT GROUNDED]                             |
|            v                                                                |
|   [PASSED] Deactivate/Remove + Placard "INOPERATIVE" + PIC Determination    |
+-----------------------------------------------------------------------------+

The Four Legal Checkpoints Explained

1. Type Certificate Data Sheet (TCDS) / Certification Regulations

• Is the item part of the VFR-day type certification requirements under which the aircraft was certificated (e.g., Civil Air Regulations CAR 3, 14 CFR Part 23)?
• Example: If an aircraft's TCDS lists a specific fuel pressure gauge as required equipment for base airworthiness certification, the aircraft cannot fly without it.

2. Kinds of Operations Equipment List (KOEL) & POH Equipment List

• Most modern aircraft Flight Manuals (POH/AFM Section 2 or 6) contain a Kinds of Operations Equipment List (KOEL) or Comprehensive Equipment List specifying equipment required for specific operational categories (VFR Day, VFR Night, IFR Day, IFR Night, Icing).
• Example: An electric pitot heat system might be optional for VFR Day, but the KOEL lists pitot heat as required (quantity: 1) for IFR operations. If pitot heat fails prior to an IFR flight, it fails Step 2 and the aircraft is grounded for IFR.

3. 14 CFR Part 91 Operational Rules (91.205, 91.207, 91.215, 91.225)

• Is the instrument required by 14 CFR 91.205 for the specific flight category?
  • VFR Day: 91.205(b) ATOMATO FLAMES
  • VFR Night: 91.205(c) FLAPS
  • IFR Flight: 91.205(d) GRABCARD
  • High Altitude: 91.205(e) DME / RNAV at >= FL240
  • Transponder / ADS-B: 91.215 & 91.225 for controlled airspace
• Example: An inoperative attitude indicator is not required for VFR Day, but it is explicitly mandated by 91.205(d)(4) for IFR. It cannot be deferred for an IFR departure.

4. Airworthiness Directives (ADs)

• Is the item required to be operational by any mandatory Airworthiness Directive issued under 14 CFR Part 39?
• Example: An AD requiring an operational secondary electric fuel pump or modified fuel selector valve cannot be bypassed or deferred.

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4. Deactivation, Placarding & Removal Protocols

If the inoperative item passes all four checkpoints (meaning it is not legally required by TCDS, KOEL, 91.205, or ADs), 14 CFR 91.213(d)(3) requires one of two physical actions:

1. Complete Removal: The inoperative instrument or equipment is physically removed from the aircraft, the cockpit opening covered, and the aircraft's weight and balance records updated in the maintenance logbook by an A&P mechanic.
2. Deactivation & Placarding:
   • Deactivation: The equipment must be rendered completely inoperable to prevent accidental activation. Typical deactivation methods include pulling the corresponding circuit breaker and installing a mechanical lockout collar, turning off and safeties a dedicated switch, or disconnecting electrical connectors (if permitted as pilot preventive maintenance or completed by maintenance personnel).
   • Placarding: The instrument, switch, or panel control must be visibly placarded "INOPERATIVE" or "INOP" in clear view of the pilot.

[!WARNING] Deactivation vs. Complex Disassembly: Simple deactivation—such as pulling and collaring an individual circuit breaker or securing a switch—may be performed by the pilot. However, if deactivation requires extensive disassembly, rewiring, or altering primary flight systems, it constitutes maintenance and must be performed and logged by an authorized A&P mechanic under 14 CFR Part 43.

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5. Pilot-in-Command Airworthiness Determination

Passing the 4-step regulatory filter and placarding the item does not automatically make the flight prudent. Under 14 CFR 91.213(d)(4), the final legal hurdle is the Pilot-in-Command Airworthiness Determination.

The PIC must determine that the inoperative instrument or equipment does not constitute a hazard to the safety of flight under the planned operating conditions.

Practical IFR Scenario Analysis:

• Scenario A: Inoperative Autopilot for Single-Pilot IFR: The autopilot is not required by 91.205(d) for Part 91 operations. It is legally deactivated and placarded INOP. However, the pilot is single-pilot planning a 400 NM night cross-country in low IMC with turbulence. The PIC must evaluate personal workload and fatigue. Flying without an autopilot in severe IMC may constitute an unacceptable hazard.
• Scenario B: Inoperative Secondary Comm Radio: The aircraft has dual VHF comms. Comm 2 fails. 91.205(d) requires "a two-way radio communications system" (singular). Legally, Comm 1 satisfies the rule. If the flight is in benign VMC along a radar-vectored route, the PIC may determine the flight is safe. If the route crosses remote mountainous terrain with known frequency dead zones, losing the only remaining comm radio would be catastrophic.

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6. Documenting In-Flight and Postflight Discrepancies

The 14 CFR § 91.213 machinery above only works if squawks actually get written down. The Instrument Rating ACS devotes an entire Area of Operation — Area VIII, Postflight Procedures — to a single knowledge element: the procedures for documenting in-flight and postflight discrepancies. The FAA expects the same discipline on a rented Skyhawk as on a Part 121 jet.

The Regulatory Chain

Note the division of labor the FAA builds into these rules: the pilot writes up the discrepancy, but only an authorized mechanic clears it. A pilot who erases their own squawk, or who simply resets a breaker and says nothing, has broken the chain that § 91.405 depends on.

What a Compliant Discrepancy Write-Up Contains

1. Date, aircraft registration, and tachometer/Hobbs time at which the discrepancy was observed.
2. A factual description of the symptom, not a diagnosis. Write "Attitude indicator showed a 5° left bank in level cruise, suction 4.2 in Hg" rather than "vacuum pump bad." Maintenance troubleshoots faster from symptoms.
3. Phase of flight and conditions — cruise, approach, in IMC, in icing, after a hard landing, with pitot heat on.
4. Whether the item was deactivated or placarded, and by whom.
5. The pilot's name and signature in the aircraft discrepancy log / squawk sheet, so the owner-operator has a dated record to act on.

The Postflight Instrument and Equipment Check

An instrument-flight postflight is not just a walk-around for hangar rash. Before shutdown and immediately after, verify and note:

• Gyro spool-down and flags: Listen for abnormal bearing noise as vacuum gyros run down; confirm no warning flags stayed in view during the flight.
• Suction and ammeter trend: Compare against the values recorded at run-up; a drifting suction gauge is the classic pre-failure signature of an engine-driven vacuum pump.
• Avionics and database messages: Note any RAIM, WAAS, "DATABASE EXPIRED," or cross-check miscompare messages the system generated en route.
• Pitot-static and antennas: Inspect the pitot mast, static ports, and antennas for ice residue, insect nests, or damage — then install the pitot cover.
• Airframe: Look for residual ice, prop-strike evidence, tire flat-spots, and leaks under the cowl.

[!WARNING] The "I'll just tell the next pilot" trap. A verbal handoff is not documentation, does not satisfy 14 CFR § 91.405, and does not survive a shift change. Anything you would want to know before launching into night IMC belongs in the squawk book. If a malfunction also produced a deviation from a clearance or a regulation, a NASA Aviation Safety Reporting System (ASRS) report filed within 10 days is a separate — and voluntary — protection.

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7. Special Flight Permits (Ferry Permits)

If an aircraft has inoperative equipment that fails the 14 CFR 91.213(d) filter (e.g., an airspeed indicator, altimeter, or structural component required for airworthiness) but is capable of safe flight to a repair facility, the owner/operator must obtain a Special Flight Permit (commonly called a Ferry Permit) under 14 CFR § 21.197 and § 21.199.

Special Flight Permit Characteristics:

• Issued by the local FAA Flight Standards District Office (FSDO) or an authorized Designated Airworthiness Representative (DAR).
• Requires an application stating purpose of flight, itinerary, crew qualifications, and any mechanical limitations.
• Usually requires an A&P inspection stating the aircraft is safe for the intended ferry flight.
• Strict Operating Limitations: Typically restricted to day VMC only, no non-essential passengers/cargo, and direct flight to the maintenance facility.