14 CFR Part 91

General operating and flight rules

Operating rules, required equipment, and the owner's maintenance and inspection duties. The 22 sections below are the ones owners, schools and pilots look up most, each explained in plain English beside the official text.

91.3Pilot in command authorityThe pilot in command is directly responsible for, and is the final authority as to, the operation of the aircraft. In an in-flight emergency that needs immediate action, the pilot may deviate from any Part 91 rule as far as the emergency requires.
91.7Flying only an airworthy aircraftNo one may operate a civil aircraft that is not airworthy. The pilot in command decides whether the aircraft is in condition for safe flight and must end the flight if an unairworthy condition appears.
91.9Flight manual, markings and placardsYou must fly within the operating limitations in the approved flight manual and on the aircraft's markings and placards. A current approved flight manual, or the approved manual material and placards for older aircraft, has to be in the aircraft.
91.17Alcohol and drugs: the eight-hour ruleNo one may act as a crewmember within 8 hours of drinking alcohol, while under its influence, with an alcohol concentration of 0.04 or more, or while using any drug that impairs them. Pilots also may not carry an intoxicated passenger, except in an emergency or a medical patient under care.
91.103Preflight actionBefore every flight the pilot in command must become familiar with all available information about it. That always includes runway lengths and takeoff and landing distances. For IFR flights and flights away from the airport it also includes weather, fuel, alternatives and known ATC delays.
91.147Sightseeing flights for compensation (LOA)An operator selling nonstop passenger flights that start and end at the same airport, within 25 statute miles, needs a Letter of Authorization from the FAA. It must also follow the Part 136 safety rules, run a registered drug and alcohol testing program, and meet Part 5's safety management requirements.
91.151VFR fuel requirementsBefore a VFR flight, an airplane must carry enough fuel to reach the first intended landing point and then fly at normal cruise for 30 more minutes by day, or 45 minutes at night. A rotorcraft needs 20 minutes.
91.171VOR equipment check for IFRTo navigate by VOR under IFR, the aircraft's VOR equipment must have been operationally checked within the preceding 30 days and found within tolerance, unless it is maintained under an approved procedure. The pilot logs the date, place, bearing error and signature.
91.203Documents required on boardEvery civil aircraft must carry a current airworthiness certificate and an effective registration certificate. The airworthiness certificate has to be displayed at the cabin or cockpit entrance where passengers or crew can read it.
91.205Required instruments and equipmentA powered aircraft with a standard airworthiness certificate must have specific instruments and equipment working for each kind of flight. Day VFR has a basic list, night VFR adds lights and fuses, and IFR adds gyros, a clock and suitable radios.
91.207ELT inspection and battery replacementMost US-registered airplanes must carry a working emergency locator transmitter, inspected every 12 calendar months. Its battery must be replaced after 1 cumulative hour of use or when half its useful life has passed.
91.213Flying with inoperative equipmentYou may take off with inoperative equipment only under an approved Minimum Equipment List, or, for most small piston aircraft without one, if the item is not required for the flight, is removed or deactivated and placarded, and is judged not to be a hazard.
91.225ADS-B Out: where it is requiredSince January 1, 2020, aircraft need ADS-B Out to fly in Class A, B and C airspace, within the 30 nm Mode C veil, above Class B and C shelves, and in Class E at or above 10,000 feet MSL. Aircraft certificated without an engine-driven electrical system, such as gliders and many antiques, are partly exempt.
91.403The owner is responsible for airworthinessThe owner or operator is primarily responsible for keeping the aircraft airworthy, and that includes complying with every Airworthiness Directive. The mechanic does the work, but the duty to have it done sits with the owner.
91.405Maintenance the owner must have doneThe owner or operator must have the aircraft inspected as Part 91 requires and have discrepancies repaired between inspections. They must also make sure the mechanic logs every return to service and placards anything left inoperative.
91.407Flying after maintenance or alterationAfter any maintenance, preventive maintenance, rebuilding or alteration, the aircraft cannot fly until an authorized person approves it for return to service and the logbook entry is made. Work that may have changed how it flies also needs a test flight by at least a private pilot before passengers ride along.
91.409Annual and 100-hour inspectionsEvery aircraft needs an annual inspection within the preceding 12 calendar months. An aircraft that carries passengers for hire, or that an instructor provides for flight instruction for hire, also needs an annual or 100-hour inspection every 100 hours of time in service.
91.411Altimeter and pitot-static checks for IFRTo fly IFR in controlled airspace, an airplane or helicopter's static system, altimeters and altitude reporting equipment must have been tested within the preceding 24 calendar months. The test is also required after the static system is opened or the encoder is worked on.
91.413Transponder tests and inspectionsAny transponder required by 91.215 must have been tested and inspected within the preceding 24 calendar months. It also needs a new test after installation or maintenance that could introduce a data correspondence error.
91.417Maintenance records an owner must keepAn owner keeps two kinds of records. Work records (what was done, when, and who signed it) are kept until the work is repeated or superseded, or for a year. Status records (total time, life-limited parts, overhaul times, inspection status, AD status and Form 337s) stay with the aircraft for good and transfer when it is sold.
91.419Maintenance records when an aircraft is soldWhoever sells a US-registered aircraft must give the buyer its status records from 91.417(a)(2) at the time of sale, and its work records too, although the buyer can let the seller keep physical custody of those.
91.421Records for a rebuilt engineAn engine rebuilt by its manufacturer, or by an agency the manufacturer approves, may start a new maintenance record with no previous history. That is what zero time means; an overhauled engine does not qualify.

The rest of Part 91 is on the eCFR.