FAR Ninety-One Point Two One Three, the Four-Step Inoperative Equipment Decision Flow, and the Burned-Out Bulb That Does Not Have to Ground Your Flight

FAR 91.213 establishes the legal framework for operating a civil aircraft with inoperative instruments or equipment. Rather than requiring every broken item to be fixed before flight, it provides a structured four-step analysis that separates safety-critical failures from inconsequential ones. Knowing this process is a core pilot-in-command responsibility - and it comes up on checkrides.

Does Your Aircraft Have a Minimum Equipment List?

The first question before any analysis is whether the aircraft has a Minimum Equipment List (MEL).

An MEL is an FAA-approved document specific to a particular aircraft make and model. It formally defines which items can be inoperative, under what conditions, and what procedures must be followed before dispatch. Airlines and many charter operators use them. An MEL is not something you can draft yourself - it requires formal FAA approval.

Most general aviation training aircraft - Cessna 172s, Piper Cherokees, Diamond DA40s - do not have an approved MEL. If your aircraft does have one, it will be in the aircraft documentation and the school or owner will know. When an MEL exists, it governs the determination entirely: follow the MEL procedures, make the required entries, and you are legal.

If there is no MEL, the analysis falls under FAR 91.213(d), which is where the four-step process lives.

What Are the Four Steps Under FAR 91.213(d)?

Work through these four questions in order. If the broken item fails any single test, the aircraft does not fly until it is repaired.

Step 1: Is the Equipment Required by the Type Certificate Data Sheet?

The Type Certificate Data Sheet (TCDS) is an FAA document that defines the basic airworthiness standards for a specific aircraft type. It is not the Pilot’s Operating Handbook - it predates the POH and establishes the original certification basis for the aircraft.

If the TCDS requires a specific item, no further analysis applies. The item must be repaired. For most training scenarios, this question concerns the core primary systems and fundamental instrumentation the aircraft was certified with.

Step 2: Is the Equipment Required by an Airworthiness Directive?

Airworthiness Directives (ADs) are mandatory compliance documents issued by the FAA in response to identified unsafe conditions. If an AD applicable to your aircraft specifically requires a piece of equipment to be installed and operational, and that item is broken, you do not fly.

The practical step here is checking the aircraft’s AD compliance log. Most flight schools maintain this record. If you are uncertain whether an AD covers the inoperative item, that is a question for the maintenance department - not a determination to make alone on the ramp.

Step 3: Is the Equipment Listed as Required in the FAA-Approved AFM?

The Pilot’s Operating Handbook (POH) for most certificated aircraft contains a section called the Kinds of Operations Equipment List (KOEL). The KOEL specifies which items are required for which categories of operation: day VFR, night VFR, and IFR.

This is aircraft-specific. The KOEL for a Cessna 172S is not the same as the KOEL for a Piper Archer III. Read the actual document for your actual airplane.

When the KOEL states an item is required for a given kind of operation, that carries the same legal weight as the regulation itself for airworthiness purposes. It is not a suggestion.

Know where the KOEL is before you need it. It typically appears in Section 2 (Limitations) or as a supplement to Section 2. In some older aircraft it is embedded differently. Finding it during a time-pressured preflight is not the right moment to discover you have never opened that section.

Step 4: Is the Equipment Required by the FARs for Your Specific Operation?

FAR 91.205 lists required instruments and equipment for powered civil aircraft, broken down by type of operation.

Day VFR requirements include:

• Airspeed indicator
• Altimeter
• Magnetic direction indicator (compass)
• Fuel gauge for each fuel tank
• Oil pressure gauge for each engine with a pressure lubrication system
• Oil temperature gauge for each air-cooled engine
• Manifold pressure gauge for each altitude engine
• Tachometer for each engine
• Temperature gauge for each liquid-cooled engine
• Anti-collision light system for aircraft manufactured after March 1, 1996
• Emergency locator transmitter (ELT)

Night VFR adds to the day VFR list:

• Functioning position lights
• Anti-collision light system
• Adequate source of electrical energy for all electrical and radio equipment
• One spare set of fuses, if applicable

Notice what is absent from the day VFR list: navigation lights. The red port, green starboard, and white tail lights are not required for day operations under 91.205.

How Does the Four-Step Analysis Work on a Real Scenario?

Consider the opening scenario: a burned-out starboard nav light discovered on preflight for a day VFR cross-country.

• TCDS: For most common training aircraft, basic navigation lights are not a TCDS airworthiness requirement for day operations.
• Airworthiness Directives: Check the aircraft records. For most common trainers, no AD mandates nav light operability for day operations. Verify - do not assume.
• POH/KOEL: Open the AFM for your specific aircraft. Under Day VFR, the position lights in many common trainers are listed as required for night operations only. Your aircraft may differ - read it.
• FARs: FAR 91.205 does not list position lights as required for day VFR.

If all four questions return no, the aircraft may legally be operated with that inoperative item - with conditions.

What Must Happen Before Flying with Inoperative Equipment?

Passing the four-step analysis is not the end of the process. Two additional conditions must be met.

First, the inoperative item must be either removed from the aircraft or deactivated. If deactivated rather than removed, it must be placarded inoperative. That placard is not paperwork - it is a communication device. It tells every subsequent pilot, inspector, and renter that this item is known inoperative and has been determined acceptable for the intended operation. Without the placard, there is no legal inoperative equipment determination.

Second, the deactivation must be accomplished in accordance with Part 43 of the FARs. A certificated mechanic with appropriate ratings - or a certificated pilot-owner performing authorized preventive maintenance - must deactivate the item properly and make a correct logbook entry describing the work performed and the regulatory basis.

The logbook entry is essential. In an FAA inspection or investigation, the maintenance record must support the determination. No entry means no paper trail, even if the analysis was correct.

The pilot in command makes the airworthiness determination. The physical steps of deactivating the item and making the logbook entry belong to a certificated mechanic. When renting from a flight school, that means talking to the maintenance department - not covering a switch with tape and calling it a placard.

How Do These Rules Apply to Common Inoperative Items?

Aircraft clock inoperative. Not required by the TCDS. Typically no applicable AD. Most KOEL entries do not list the clock as required for day or night VFR. Not required by 91.205. Deactivate, placard, log entry - mission proceeds.

Pitot heat inoperative, day VFR, no forecast icing. Pitot heat is not listed by 91.205 as required for day VFR operations absent icing conditions. Check the KOEL - some manufacturers require it in their approved documentation. Regardless, flying into any conditions where pitot icing is possible without functioning pitot heat is a safety issue independent of the legal analysis. The regulation may permit the determination; airmanship may still ground the flight.

Transponder inoperative. The analysis changes significantly based on where you are flying. In Class A, Class B, and Class C airspace, and within the Mode C veil extending 30 nautical miles around Class B airports, a functioning transponder with altitude encoding is required by FAR 91.215. In most other controlled airspace, a transponder is practically required for ATC services. Operating without a transponder in controlled airspace requires an ATC authorization. For student operations, a broken transponder is almost always a grounding item. Do not work through this without your instructor.

ADS-B Out inoperative. Since January 1, 2020, ADS-B Out is required in the same airspace that requires the transponder and altitude encoder. A broken ADS-B Out unit triggers the same authorization requirement. Treat it identically to a transponder issue and involve the school before flying in that airspace.

How Should You Handle Inoperative Equipment on a Checkride?

If an item is placarded inoperative in the aircraft on the day of your private pilot checkride, do not be unsettled. Know the analysis.

Be prepared to walk through the four questions: why the placard is there, what kind of operation it does or does not restrict, and why the aircraft remains airworthy for the intended flight. That level of systematic thinking is exactly what the Airman Certification Standards are designed to evaluate.

Arriving and being unable to explain it is a problem. Arriving and explaining it fluently is the mark of a pilot the examiner wants to pass.

Key Takeaways

• FAR 91.213(d) provides a four-step decision process - TCDS, ADs, POH/KOEL, and FARs - that must all be checked before flying with inoperative equipment.
• If the aircraft has an approved MEL, the MEL governs the determination entirely; the four-step analysis only applies when no MEL exists.
• Position lights are not required for day VFR under FAR 91.205 - a burned-out nav light is not automatically a grounding item for a daytime flight.
• Passing the four-step analysis requires two additional steps: a proper deactivation or removal, an inoperative placard, and a Part 43 logbook entry by a certificated mechanic.
• The pilot in command bears the legal responsibility for the airworthiness determination - “I didn’t know” and “I assumed someone else handled it” are not valid defenses.