AC 91-67 Minimum Equipment Requirements for Part 91

To fly IFR under Part 91, your aircraft must carry everything 14 CFR 91.205(d) lists for instrument flight, on top of the day and night VFR equipment in 91.205(b) and (c), and several inspection-based items (ADS-B Out, transponder, altimeter and static system, and VOR if used) must be current.¹ The IFR required equipment under Part 91 is the sum of those lists, and 14 CFR 91.213 governs what to do when any of it stops working.² Advisory Circular 91-67A explains one FAA-accepted method for meeting these rules, but the binding law is in the regulations themselves.³

The 91.205(d) IFR Instrument List

On top of everything required for VFR flight, 91.205(d) adds nine items for IFR.⁴ Many pilots memorize them with the mnemonic GRABCARD (generator, rate-of-turn, attitude indicator, ball, clock, altimeter, radios, directional gyro):

Two-way radio communication and navigation equipment appropriate for the route being flown.
A gyroscopic rate-of-turn indicator. This is not required if the airplane has a third attitude instrument system usable through 360 degrees of pitch and roll, or if a rotorcraft has a third attitude system covering ±80 degrees of pitch and ±120 degrees of roll.
A slip-skid indicator, the ball that shows coordinated flight.
A sensitive altimeter adjustable for barometric pressure through the Kollsman window.
A clock displaying hours, minutes, and seconds, with a sweep-second hand or digital equivalent.
A generator or alternator of adequate capacity to power all required electrical and radio equipment continuously.
A gyroscopic pitch and bank indicator (artificial horizon).
A gyroscopic direction indicator (directional gyro or equivalent).

Every one of these must be operable before departure. A dead artificial horizon or failed directional gyro grounds the aircraft for IFR. The rule allows FAA-approved equivalents, which is how modern glass-panel installations satisfy language originally written for individual round-dial instruments.

The VFR Baseline You Also Need

IFR flight requires everything on the day VFR and night VFR lists as well, and it’s easy to overlook.¹

For day VFR, 91.205(b) requires:

Flight instruments: airspeed indicator, altimeter, and magnetic direction indicator.
Engine instruments: tachometer for each engine, oil pressure gauge for each engine with a pressure system, oil temperature gauge for each air-cooled engine, temperature gauge for each liquid-cooled engine, manifold pressure gauge for each altitude engine, and fuel quantity gauges for each tank.
Safety equipment: approved seatbelts with metal-to-metal latching for each occupant, shoulder harnesses for applicable seats, a landing gear position indicator if the gear is retractable, an ELT if required by 91.207, and an anticollision light system on small airplanes certificated after March 11, 1996.

Night VFR adds position lights, an anticollision light system, an adequate electrical power source for all installed electrical and radio equipment, spare fuses accessible to the pilot, and a landing light if the aircraft is operated for hire.

Airspace and Inspection Rules That Decide Legality

The 91.205(d) list gets most of the attention, but four other rules do just as much to determine whether a given IFR flight is legal.

ADS-B Out

Since January 1, 2020, ADS-B Out meeting the standards in 91.225 has been required in Class A, B, and C airspace, within the Mode C veil of most major airports, and in Class E airspace at or above 10,000 feet MSL, among other areas.⁵ Because IFR flights in controlled airspace pass through at least some of these areas, ADS-B Out is effectively mandatory for most IFR operations. Flying IFR without it limits you to uncontrolled airspace below 10,000 feet.

Transponder

A Mode C transponder is required in much of the same airspace as ADS-B Out. It must also be tested and inspected every 24 calendar months by a qualified repair station or other authorized entity, in accordance with appendix F of Part 43.⁶ An expired transponder check is a common squawk that catches pilots off guard during a ramp check.

Altimeter and Static System

Under 91.411, no one may operate an airplane or helicopter IFR in controlled airspace unless the static pressure system, each altimeter, and the automatic altitude reporting system have been tested within the preceding 24 calendar months.⁷ Testing must comply with appendices E and F of Part 43, and only the aircraft manufacturer, a properly rated repair station, or (for static system tests only) a certificated mechanic with an airframe rating may perform it. If anyone opens and closes the static system for any reason other than using the drain or alternate static valve, the system must be retested before the next IFR flight.

VOR Check

If you plan to use VOR navigation for IFR, 91.171 requires an operational check within the preceding 30 days.⁸ The check can be done using an FAA-operated test signal, a designated ground checkpoint, an airborne checkpoint, or a dual-VOR cross-check. Allowable bearing error is ±4 degrees for ground-based checks and ±6 degrees for airborne checks. You must log the date, place, and bearing error, and sign the entry.

Recurring Inspection Deadlines at a Glance

Scheduling the altimeter/static and transponder checks together makes sense since many avionics shops handle both at the same appointment.

When Something Breaks

14 CFR 91.213 sets out a two-track system for deciding whether an aircraft with an inoperative item can still fly.²

With an Approved MEL

If the aircraft has an FAA-approved Minimum Equipment List, you follow it. The MEL is type-specific and spells out which items can be inoperative, under what conditions, for how long, and what operational limitations apply. Approval is coordinated through the local Flight Standards District Office, starting from a Master Minimum Equipment List for the aircraft type; the operator’s own procedures document may be more restrictive than the MMEL but never less.⁹ Most Part 91 piston operators don’t pursue an MEL because of the approval workload.

Without an MEL

Most general aviation pilots operate under 91.213(d), which covers non-turbine airplanes, rotorcraft, gliders, and similar aircraft. The inoperative item must not be required by any of the following, or the aircraft cannot fly:

The VFR-day airworthiness standards under which the aircraft was originally type certificated.
The aircraft’s equipment list or Kinds of Operations Equipment List (KOEL). If the KOEL says an item is required for IFR, it cannot be deferred for an IFR flight.³
14 CFR 91.205 or any other Part 91 rule that applies to the kind of flight planned.
Any applicable Airworthiness Directive.

Even after the item clears those four gates, two steps remain. The equipment must be physically removed with the cockpit control placarded, or deactivated and placarded “Inoperative,” with maintenance recorded under Part 43 where applicable. Then a certificated pilot or maintenance person must determine that the inoperative item does not create a hazard.² The regulation does not define “hazard,” so that determination has to account for the actual conditions of the planned flight.

Common Pitfalls

A few mistakes come up repeatedly. Pilots confuse the equipment list in the Pilot’s Operating Handbook with the KOEL; not every aircraft has a KOEL, and the format varies by manufacturer, so you need to know where your aircraft documents its required equipment for each kind of operation. Pilots also assume the annual inspection covers the 24-month altimeter/static and transponder checks. It doesn’t. Those are separate inspections to different standards, and the due dates won’t necessarily line up with the annual. Finally, switching off a broken instrument and flying without placarding or logging it violates 91.213(d) even if the item wasn’t required for the flight.