FAR Ninety-One Point Two Thirteen, the Inoperative Equipment Decision Tree, and the Step-by-Step Process That Decides Whether Your Airplane Can Legally Fly

FAR 91.213 provides a structured, four-question decision tree for determining whether an aircraft with inoperative equipment is legal to fly. Understanding this regulation prevents two equally costly mistakes: flying when you shouldn’t, and grounding an airplane that would have been perfectly legal to take. Every pilot needs this framework before they ever find a broken gauge on the ramp.

Does Your Aircraft Have a Minimum Equipment List?

The first question under FAR 91.213 is whether your aircraft has a Minimum Equipment List (MEL) - an FAA-approved document specifying which instruments and equipment can be inoperative for a particular kind of operation. Airlines and some charter operators use them. If your aircraft has an MEL, consult it. The MEL tells you exactly what can and cannot be deferred, and that ends the analysis.

Most general aviation aircraft - your Cessna 172, Piper Cherokee, Beechcraft Bonanza - do not have MELs. If yours doesn’t, you work through the decision tree yourself.

What Are the Four Questions You Must Ask in Order?

There are four questions to ask sequentially. If the answer to any single question is yes, the aircraft is not airworthy for that flight. If all four answers are no, you may be able to proceed legally - with specific requirements.

Question 1: Is the equipment required by the aircraft’s type certificate data sheet, flight manual, or approved equipment list?

Every certificated aircraft has a type certificate, and the documents flowing from it - including the Pilot’s Operating Handbook and the AFM equipment list - may designate certain equipment as required. This varies by model and sometimes by serial number. The only way to know is to consult your specific aircraft’s documentation. An instrument can appear on your aircraft’s required list even if it is not on the regulatory required list. This question comes first, and it is aircraft-specific.

Question 2: Is the equipment required by FAR 91.205?

FAR 91.205 specifies required instruments and equipment for different operations. For day VFR flight, the required items are remembered with the acronym TOMATO FLAMES: Tachometer, Oil pressure, Manifold pressure gauge (altitude engines), Altimeter, Temperature gauge (liquid-cooled engines), Oil temperature (air-cooled engines), Fuel gauge for each tank in use, Landing gear position indicator (retractable gear), Airspeed indicator, Magnetic compass, Emergency locator transmitter, and Safety belts. Aircraft certificated after August 1971 also require an approved anticollision light system.

Knowing the acronym is the beginning of the analysis, not the end of it.

Question 3: Is the equipment required by an Airworthiness Directive?

Airworthiness Directives (ADs) are mandatory FAA compliance documents issued when a safety issue exists with a specific aircraft type, component, or system. Some ADs require particular equipment to be installed and operational as a condition of continued airworthiness. If an AD covers the broken item and requires it to be functional, the aircraft is not airworthy. The AD makes it required equipment regardless of what 91.205 says.

Question 4: Is the equipment required by any other operating rule?

This catch-all covers requirements the first three questions may not have addressed. Emergency locator transmitters are a practical example: FAR 91.207 separately mandates ELTs for most operations. A dead ELT battery may not surface in questions one through three, but it disqualifies the flight under question four.

What Happens If All Four Answers Are No?

If the inoperative item is not required by any of the four criteria above, FAR 91.213 permits you to continue - but only after completing three specific steps.

Step 1: Deactivate or remove the equipment. A broken instrument that actively displays false or misleading information cannot remain in service. Pull the circuit breaker and collar it. If deactivation or removal requires maintenance work, a certificated mechanic performs that work.

Step 2: Placard the instrument. A label reading “INOPERATIVE” must be placed at or near the instrument in the cockpit. This is a regulatory requirement, not a recommendation. It ensures every pilot who flies that aircraft knows the item is not functioning.

Step 3: Determine the inoperative equipment does not constitute a hazard. The regulation places this judgment call directly on you as pilot in command. Legal and safe are not always the same thing. The regulation may open the door - your judgment decides whether you walk through it.

Where Do Pilots Most Commonly Get This Wrong?

The fuel gauge scenario catches pilots consistently. A pilot physically checks fuel quantity with a fuel stick during preflight, measures accurately, climbs in, and finds the left fuel gauge reading erratically. The reasoning goes: I know the fuel is there, so I can go. This is incorrect. FAR 91.205 specifically requires a fuel gauge indicating the quantity of fuel in each tank being used. A gauge that does not provide a reliable indication is inoperative required equipment. The visual check is excellent practice and should always be done, but it does not satisfy the regulatory requirement for a functioning gauge - and it provides no information about fuel system issues that develop after departure.

The vertical speed indicator illustrates the other side of this. The VSI is not listed as required equipment under FAR 91.205 for day VFR flight. But Question 1 still applies: if your aircraft’s type certificate documentation lists it as required equipment, you cannot defer it regardless of what 91.205 says. This is why knowing your aircraft’s specific documentation is not optional.

How Should You Handle This on a Checkride?

An examiner will present an inoperative equipment scenario and expect to see the full decision-making process, not a regulation number. If a turn coordinator is inoperative during preflight for a cross-country, walk through it: Is there an MEL? What operation am I conducting? Is this equipment listed in the aircraft’s type certificate documentation? Is it on the 91.205 required list for this operation? Does an AD cover it? Does any other rule require it?

If all four answers are no, describe the steps: deactivate, placard, determine no hazard, make the go or no-go decision.

Examiners are evaluating the framework, not a memorized answer to one specific case. Pilots who can recite TOMATO FLAMES but have never read 91.213 tend to falter when the examiner asks what happens when something is broken. Read the actual regulation text.

What About Navigation Lights?

Position lights are a useful case study in how operational context changes the analysis. For night VFR flight, approved position lights are required by 91.205 - non-negotiable. For day VFR flight, they are not on the 91.205 required list. A burned-out nav light discovered before a day VFR flight, if not required by the aircraft’s type certificate documentation, could potentially be placarded as inoperative and the flight conducted in daylight.

The judgment call is this: if there is any possibility the flight extends into civil twilight or later, fix the light before departure. The moment conditions reach night, an inoperative position light creates a 91.205 violation. Consider the full intended operation before making the call.

Who Can Perform the Maintenance Work?

When inoperative equipment requires maintenance before the aircraft can legally fly, that work belongs to a certificated mechanic. Pilots may perform preventive maintenance on aircraft they own or operate under the circumstances defined in FAR 43.3, but that scope is limited. The determination of airworthiness and the logbook entry certifying a return to service are the mechanic’s responsibility. Know where that line is before you start turning wrenches.

Key Takeaways

• FAR 91.213 provides a four-question decision tree: type certificate requirements, FAR 91.205 required equipment, Airworthiness Directives, and other applicable operating rules - if any answer is yes, the aircraft is not airworthy.
• Most general aviation aircraft have no MEL, so pilots must work through the decision tree themselves using the aircraft’s actual documentation, not just the regulatory list.
• If all four questions clear, you must deactivate the equipment, placard it “INOPERATIVE,” and determine as pilot in command that it does not constitute a hazard.
• A functioning fuel gauge is a regulatory requirement under 91.205 - a visual fuel check does not substitute for it.
• Legal and safe are not the same thing. The regulation sets the floor; your judgment as PIC determines whether the flight should happen.