Part 91 Series — Required Documents & Equipment: What Must Be in the Airplane (and Working)

You’ve planned the flight.
You’ve checked the weather.
You’ve calculated fuel.

But before you taxi, there’s another critical question:

Is the airplane itself legal to fly?

Under FAR Part 91, legality isn’t just about pilot certificates and fuel reserves. The aircraft must carry specific documents — and certain instruments and equipment must be installed and operable.

In small aircraft, this often comes down to very practical questions:

• Is the POH required on board?

• What if the landing light is burned out?

• Can I fly with an inoperative fuel gauge?

• When is a transponder required?

• What about the ELT?

In this third article of our 8-part Part 91 series, we’ll break down the regulations governing:

• Required aircraft documents

• Required equipment (Day/Night VFR and IFR)

• ELT rules

• Transponder requirements

• Inoperative equipment procedures

These are the rules that determine whether you’re legally airworthy — before the wheels move an inch.

Let’s open the glovebox.

The Legal Basics: Documents & Required Equipment

In this article, we’re covering:

• §91.203 — Required aircraft documents

• §91.205 — Required instruments and equipment

• §91.207 — Emergency Locator Transmitters (ELTs)

• §91.213 — Inoperative instruments and equipment

• §91.215 — ATC transponder requirements

Together, these regulations define what must be on board and what must be operational.

§91.203 — Required Aircraft Documents (ARROW)

No person may operate a civil aircraft unless it has the appropriate and current documents on board.

Most pilots remember this with the acronym ARROW:

• Airworthiness Certificate

• Registration Certificate

• Radio Station License (required only for international operations)

• Operating Limitations (AFM/POH and placards)

• Weight and Balance information

Let’s break that down for small-aircraft pilots:

Airworthiness Certificate

Must be displayed at the cabin or cockpit entrance so it is legible to passengers.

Registration Certificate

Must be current. Temporary registration documents must also be valid.

Operating Limitations

This includes:

• The approved Airplane Flight Manual (AFM) or POH (if required)

• Required placards

• Markings

The POH isn’t just helpful — it’s regulatory when required by the type certificate.

Weight and Balance

The aircraft must have current weight and balance data.

No ARROW? No legal flight.

§91.205 — Required Instruments & Equipment

This regulation defines what must be installed and operable for different types of operations.

Day VFR — “TOMATO FLAMES”

For small aircraft operating day VFR, required equipment includes:

• Tachometer

• Oil pressure gauge

• Manifold pressure gauge (if applicable)

• Altimeter

• Temperature gauge (liquid-cooled engines)

• Oil temperature gauge

• Fuel gauge for each tank

• Landing gear position indicator (if retractable)

• Airspeed indicator

• Magnetic direction indicator

• ELT

• Seatbelts

Note: Fuel gauges are required for each tank. An inoperative fuel gauge is not something you can legally ignore.

Night VFR — Add “FLAPS”

For night VFR, add:

• Fuses or spare circuit breakers

• Landing light (if operated for hire)

• Anti-collision lights

• Position lights

• Source of electrical energy

IFR Equipment

For IFR operations, additional equipment includes:

• Gyroscopic rate-of-turn indicator

• Slip-skid indicator

• Sensitive altimeter

• Clock with seconds display

• Generator or alternator

• Gyroscopic pitch and bank indicator

• Gyroscopic direction indicator

The specifics matter — especially for instrument-rated private pilots.

§91.207 — ELT Requirements

Most civil aircraft must be equipped with an approved Emergency Locator Transmitter (ELT).

Key requirements:

• Must be inspected every 12 calendar months

• Battery must be replaced or recharged after:

  • 50% of useful life has expired, or

  • 1 cumulative hour of use

There are limited exceptions (e.g., certain local training flights), but for most GA operations, an operable ELT is required.

§91.215 — Transponder Requirements

A transponder with Mode C (altitude reporting) is required in:

• Class A, B, and C airspace

• Within 30 NM of Class B primary airports (Mode C veil)

• Above 10,000 feet MSL (with certain exceptions)

Most modern aircraft also require ADS-B Out under separate regulations, but transponder requirements remain foundational.

At this level, you now understand what must be onboard and operational before departure.

But the most common real-world question isn’t about perfect airplanes.

It’s about broken ones.

Inoperative Equipment: When Can You Legally Fly?

Let’s talk about §91.213 — one of the most misunderstood sections in Part 91.

§91.213 — Inoperative Instruments and Equipment

If equipment required by §91.205 is inoperative, you generally cannot fly.

However, if equipment is not required by:

• §91.205

• The aircraft’s type certificate

• An Airworthiness Directive (AD)

• The POH

• Or other regulations for the specific operation

…it may be permissible to operate the aircraft under certain conditions.

For non-MEL aircraft (most small GA airplanes):

1. The inoperative item must be removed or deactivated.

2. It must be placarded “INOPERATIVE.”

3. A maintenance entry must be made (if required).

4. The PIC must determine that the aircraft is safe for operation.

This does not apply to required equipment like:

• Fuel gauges

• Airspeed indicators

• Required transponder (when in required airspace)

Those must be operational.

The Practical Decision Tree

When something doesn’t work:

1. Is it required for the type of flight?

2. Is it required by the POH or type certificate?

3. Is it required by regulation for the airspace?

4. Can it be safely deactivated and placarded?

If the answer to #1–3 is yes → fix it before flight.

If the answer is no → follow §91.213 procedures carefully.

Why This Matters

Flying with inoperative equipment without proper evaluation can lead to:

• Enforcement action

• Insurance complications

• Safety hazards

Most ramp inspections begin with documents and equipment.

Preparation prevents awkward conversations.

Looking Ahead

In Article 4, we’ll move into:

• VFR weather minimums

• Special VFR

• VFR cruising altitudes

• Airspace operating rules

In other words: once you’re airborne, what conditions must exist to stay legal?

Because even if your airplane is perfectly equipped… the sky still has rules.

Until then:

Check ARROW.
Know your TOMATO FLAMES.
And don’t ignore that “small” inoperative item without checking the regulation first. 🛩️