14 CFR Part 91: Operating Rules for GA pilots

Title 14 of the Code of Federal Regulations, Part 91, establishes the general operating and flight rules for civil aircraft within the United States. It applies to every person operating an aircraft in US airspace, from student pilots flying solo to ATP certificate holders on personal flights. Part 91 is the regulatory backbone of general aviation.

Unlike Parts 121 (scheduled air carriers) and 135 (commuter and on-demand operations), Part 91 generally places primary responsibility on the pilot in command. Section 91.3 states that the PIC is directly responsible for, and is the final authority as to, the operation of the aircraft. This authority includes the ability to deviate from any rule in an in-flight emergency to the extent required to meet that emergency.

Part 91 covers an enormous range of topics: preflight requirements, flight rules, equipment and instruments, maintenance, and special flight operations. This guide focuses on the sections most critical to GA pilots operating under VFR and IFR in the national airspace system.

Section 91.155 defines the basic VFR weather minimums — the minimum flight visibility and distance from clouds required for VFR flight. These minimums vary significantly by airspace class and altitude, and confusing them is one of the most common errors on the private pilot knowledge test.

Class A airspace: VFR flight is not permitted. All operations in Class A (18,000 MSL to FL600) must be conducted under IFR.

Class B airspace:3 statute miles visibility and clear of clouds. The "clear of clouds" provision is unique to Class B — all traffic is separated by ATC, eliminating the need for cloud clearance buffers.

Class C, D airspace: 3 statute miles visibility with cloud clearance of 500 feet below, 1,000 feet above, and 2,000 feet horizontal.

Class E airspace: Below 10,000 MSL, the minimums mirror Class C/D — 3 SM visibility, 500/1,000/2,000 ft cloud clearance. At and above 10,000 MSL, minimums increase to 5 SM visibility and 1,000 feet below, 1,000 feet above, 1 SM horizontal from clouds.

Class G airspace: Minimums depend on altitude (above or below 1,200 AGL), time of day, and whether you are at or above 10,000 MSL. During the day below 1,200 AGL, the minimum is 1 SM visibility and clear of clouds. At night below 1,200 AGL, it increases to 3 SM visibility with 500/1,000/2,000 ft clearance.

Fuel requirements (91.151 / 91.167): For VFR flights, no person may begin a flight unless the aircraft carries enough fuel to fly to the first point of intended landing and, assuming normal cruising speed, fly after that for at least 30 minutes during the day or 45 minutes at night. For IFR flights (91.167), the aircraft must carry enough fuel to complete the flight to the first airport of intended landing, fly from that airport to the alternate (if required), and then fly for 45 minutes at normal cruising speed.

Right-of-way rules (91.113):When weather conditions permit (regardless of IFR or VFR flight plan), each pilot must maintain vigilance to see and avoid other aircraft. The right-of-way hierarchy is precise: an aircraft in distress has right-of-way over all others. When aircraft of the same category converge at approximately the same altitude, the aircraft to the other's right has right-of-way. An aircraft being overtaken has right-of-way, and the overtaking aircraft must alter course to the right. When two aircraft approach head-on, each must alter course to the right.

The full right-of-way category hierarchy: balloons yield to no other category. Gliders yield only to balloons. Airships yield to balloons and gliders. Powered aircraft yield to all three. An aircraft towing or refueling another yields to balloons, gliders, and airships but has right-of-way over other powered aircraft.

Minimum safe altitudes (91.119): Over congested areas (cities, towns, settlements), pilots must maintain at least 1,000 feet above the highest obstacle within a 2,000-foot horizontal radius. Over non-congested areas, the minimum is 500 feet AGL except over open water or sparsely populated areas, where the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure. Over any area, altitude must be sufficient to execute an emergency landing without undue hazard to persons or property on the surface.

Cruising altitude and direction (91.159): For VFR flights above 3,000 AGL, cruising altitude is determined by magnetic course. Courses 0-179 degrees require odd thousands plus 500 feet (3,500; 5,500; 7,500). Courses 180-359 degrees require even thousands plus 500 feet (4,500; 6,500; 8,500). IFR flights (91.179) follow the same odd/even convention but at cardinal thousands.

Speed limits (91.117): Below 10,000 feet MSL, no person may operate an aircraft at an indicated airspeed exceeding 250 knots. Within 4 NM of a Class C or D airport at or below 2,500 feet AGL, the limit is 200 knots. In the Class B airspace underlying the primary airport, the limit is also 200 knots. The 10,000-foot rule exists largely for collision avoidance — at lower altitudes, slower speeds give pilots more time to see and avoid traffic.

Required instruments and equipment (91.205): Section 91.205 lists the instruments and equipment required for different types of flight. The classic mnemonic for VFR day is A-TOMATO-FLAMES: altimeter, tachometer, oil pressure gauge, manifold pressure gauge (for altitude engines), airspeed indicator, temperature gauge (for liquid-cooled engines), oil temperature gauge, fuel gauge, landing gear position indicator, anti-collision lights, magnetic compass, ELT, and seatbelts. For VFR night, add FLAPS: fuses, landing light (for hire), anti-collision lights, position lights, and source of electrical energy.

Inoperative instruments (91.213): When an instrument or item of equipment listed in 91.205 becomes inoperative, the pilot must determine whether the flight can continue legally. If the aircraft has an MEL (Minimum Equipment List) approved by the FAA, follow it. Without an MEL, use the decision tree in 91.213(d): if the item is not required by the TCDS, 91.205, 91.207 (ELT), 91.225 (ADS-B), an AD, or any other regulation, it may be deactivated and placarded inoperative.

ADS-B Out (91.225): Since January 1, 2020, ADS-B Out equipment is required in all airspace where a transponder is currently required: Class A, B, and C airspace, above the ceiling and within the lateral boundaries of Class B and C airspace up to 10,000 MSL, in Class E airspace at and above 10,000 MSL (excluding airspace below 2,500 AGL), within 30 NM of select Class B primary airports (the Mode C veil), and in airspace over the Gulf of Mexico at and above 3,000 MSL within 12 NM of the US coast.

Supplemental oxygen (91.211): At cabin pressure altitudes above 12,500 feet MSL up to and including 14,000 feet MSL, the required minimum flight crew must use supplemental oxygen for that portion of the flight at those altitudes exceeding 30 minutes. Above 14,000 feet MSL, the flight crew must use oxygen for the entire time at that altitude. Above 15,000 feet MSL, each occupant must be provided with supplemental oxygen.

Practical application for GA pilots: Part 91 is not merely a test topic — it is your operational manual. Before every flight, you should verify that weather meets the minimums for your intended airspace (91.155), that fuel quantity exceeds the legal reserve (91.151/91.167), that required equipment is installed and operative (91.205/91.213), and that ADS-B equipment is functioning if required (91.225). On the flight, observe altitude restrictions (91.119), speed limits (91.117), and right-of-way rules (91.113).

The regulations interlock. A VFR flight through Class B airspace requires ATC clearance (91.131), ADS-B Out (91.225), a Mode C transponder (91.215), meeting VFR weather minimums (91.155), and compliance with speed limits (91.117). Missing any single requirement makes the flight illegal. Understanding how these rules work together — not just in isolation — is what separates competent pilots from unsafe ones.