FAR Ninety-One Point Two Thirteen, the Inoperative Equipment Decision, and the Four-Step Test That Decides Whether You Can Still Fly Legally

FAR 91.213 - the inoperative equipment regulation - is one of the most misunderstood rules in general aviation. It applies to every part 91 pilot and gives you a clear, four-step decision framework for determining whether a broken or non-functioning piece of equipment grounds the aircraft or can be legally deactivated, placarded, and flown. Understanding this rule is essential for preflight decision-making and required knowledge for the private pilot oral exam.

What Does FAR 91.213 Actually Cover?

FAR 91.213 governs inoperative instruments and equipment for part 91 operations - personal flying, rentals, and most general aviation activity. It is not the same as a Minimum Equipment List (MEL), which applies to airline and charter operators under parts 121 and 135. For most GA pilots, 91.213 is the applicable framework, and it does not require a formal FAA approval process.

The regulation works by giving pilots a structured decision tree rather than a comprehensive list of every possible equipment scenario. The framework trusts the pilot to think, not just recite.

What Is the Four-Step Inoperative Equipment Test?

Before deciding whether to fly with broken equipment, run through all four steps in order. Each is a potential stop point.

Step 1: Is the equipment required by a Federal Aviation Regulation?

The primary reference is FAR 91.205, which lists required equipment by operation type.

For day VFR, required equipment includes: airspeed indicator, altimeter, magnetic compass, tachometer, oil pressure gauge, oil temperature gauge, fuel quantity gauges for each tank in use, emergency locator transmitter (ELT), and seatbelts.

Night VFR adds: position lights, anticollision lights, an adequate source of electrical power, and a landing light if flying for hire.

IFR adds: attitude indicator, heading indicator, sensitive altimeter, clock with a second-sweep hand or digital display, gyroscopic rate-of-turn indicator, slip/skid indicator, and DME or area navigation equipment above flight level 240.

If the broken item is on the applicable list for your planned operation, stop here. The aircraft is not airworthy for that flight. Ground it and call maintenance.

Step 2: Is the equipment required by an Airworthiness Directive?

Airworthiness Directives (ADs) are mandatory FAA safety directives. If an active AD requires a specific piece of equipment to be operational, you cannot fly without it. This step passes quickly for most routine squawks, but it must be checked. Your mechanic reviews ADs during the annual inspection; if you know an active AD is relevant to the broken item, that is a grounding event.

Step 3: Is the equipment required by the aircraft’s Kinds of Operations Equipment List (KOEL)?

The KOEL - found inside your Pilot’s Operating Handbook (POH) - is the most commonly overlooked part of this check. It is a table that lists each piece of equipment and specifies whether it is required for day VFR, night VFR, or IFR operations for that specific aircraft.

The KOEL carries legal weight equivalent to the FARs. If the KOEL requires an item for your planned operation, you are grounded regardless of whether the FARs specifically name it. Manufacturers include items on the KOEL for real engineering reasons - integrated avionics systems, specific fuel system configurations, autopilot dependencies. Know what is in your aircraft’s POH before you need this answer on the ramp.

Step 4: Is the equipment required by the aircraft’s type certificate data sheet?

This step catches items integral to the aircraft’s certification basis that may not appear elsewhere. It rarely changes the outcome for routine equipment failures, but it is part of the complete check and cannot be skipped.

What Happens If the Answer to All Four Steps Is No?

If the broken equipment is not required by any of the four checks, FAR 91.213 permits you to deactivate the equipment if possible, placard it as INOP, and legally conduct the flight.

The placard is not optional. The regulation specifically requires it. A piece of tape marked “INOP” serves a real purpose: it prevents you, future pilots, and passengers from relying on a system that is not functioning. It is a safety communication, not a paperwork formality.

What Are the Real-World Scenarios Pilots Face?

Scenario: Turn coordinator fails before a day VFR local flight. The turn coordinator is not on the day VFR required equipment list under 91.205. It is required for IFR. Assuming the KOEL does not list it as required for day VFR and no AD applies, you could legally placard it INOP and fly. However, the inclinometer ball - the slip indicator - is part of that instrument. Many pilots will decline the flight on airmanship grounds regardless of legality. Both decisions are defensible.

Scenario: Altimeter is stuck. The altimeter is on the day VFR required list. Full stop. Call maintenance.

Scenario: Left fuel quantity gauge reads empty after a confirmed full tank. Fuel quantity gauges are required by FAR 91.205, but the regulation requires them to show quantity when the selector is positioned for that tank - not that they be accurate in every condition. A broken gauge does not automatically ground the aircraft if the pilot has verified actual fuel state by direct visual inspection. You must placard it INOP, and the KOEL still applies. This nuance comes up on checkrides specifically because it requires understanding the rule, not just its surface meaning.

Scenario: ELT battery is expired. This falls under FAR 91.207, which governs ELTs separately from the main equipment list. An expired battery puts the aircraft out of compliance. Exceptions exist - flying directly to a facility to replace the battery, or operating in specific conditions where ELT carriage is not required - but the default answer is that the aircraft cannot be operated. This one surprises pilots who treat it as a maintenance note rather than an airworthiness issue.

How Does This Differ from an Airline’s Minimum Equipment List?

Airlines operating under parts 121 and 135 use FAA-approved Minimum Equipment Lists (MELs). An MEL is a formal document, specific to an aircraft type, that specifies exactly which items may be inoperative under what conditions. It is a negotiated agreement between the operator and the FAA, built for fleet operations where grounding for every squawk is operationally impractical. MELs require maintenance tracking systems and formal dispatch records.

Most part 91 GA pilots do not operate under a MEL. FAR 91.213 is the GA equivalent - a flexible framework that does not require formal FAA approval but places the judgment responsibility on the pilot in command.

What Should You Know for the Checkride?

The Airman Certification Standards for the private pilot certificate require demonstrated understanding of aircraft airworthiness, including inoperative equipment. During the oral exam, expect to walk through a scenario involving broken equipment. The examiner wants to see the four-step decision process worked out loud, not just a conclusion.

During the practical test, the examiner may present an aircraft with an item already placarded INOP. They want to know whether you notice it during preflight, what it means, and how you would decide whether to fly. The correct response is to run the four-step check on the spot. That is the answer.

Does Legal Always Mean Safe?

FAR 91.7 places a separate, ongoing responsibility on the pilot in command to determine whether the aircraft is in condition for safe flight. This is independent of the four-step equipment check.

A working number-two COM radio is not legally required for a local day VFR flight. But if the route passes through busy Class C airspace with complex arrival procedures, a pilot might reasonably decide to keep the backup radio. That is a valid airmanship call. The regulation defines the legal floor. Pilot judgment determines how much margin to maintain above it.

These are not the same thing. Knowing where the legal line sits is essential. Deciding how close to fly to that line is airmanship.

Key Takeaways

• FAR 91.213 provides a four-step test - FAR requirement, Airworthiness Directive, KOEL, and type certificate data sheet - to determine if inoperative equipment grounds the aircraft
• If all four steps return “no,” the equipment may be deactivated, placarded INOP, and the flight conducted legally
• The KOEL in your POH carries legal weight; know what it requires before preflight becomes a decision point
• FAR 91.205 governs required equipment lists by operation type - day VFR, night VFR, and IFR each carry different requirements
• Legal compliance and airworthiness are the FAA’s floor; pilot-in-command judgment under FAR 91.7 sets your personal margin above it