FAR Part 91 — General Operating and Flight Rules

14 CFR Part 91 — General Operating and Flight Rules — is the regulatory backbone of U.S. civil aviation. It applies to every civil aircraft operating in U.S. airspace unless a more specific operating rule (Parts 121, 125, 129, 135) takes precedence for a given operation. Even airline pilots flying under Part 121 are simultaneously subject to many Part 91 provisions; Part 91 is never fully displaced.

Subpart A (General) establishes the foundational responsibilities. §91.3 grants the pilot-in-command absolute authority over the safety of the flight and simultaneously imposes absolute responsibility for its conduct. §91.7 requires the PIC to determine airworthiness before flight and prohibits flight in an unairworthy aircraft. §91.9 establishes limits against exceeding aircraft weight, altitude, or speed limitations. §91.13 prohibits careless or reckless operation. These provisions are frequently cited in enforcement actions and form the basis of FAA legal action when accidents occur.

Subpart B (Flight Rules) contains the operational rules most pilots use daily. VFR weather minimums are set in §91.155 — 3 statute miles visibility and 500 ft below, 1,000 ft above, and 2,000 ft horizontal from clouds in Class G airspace below 1,200 ft AGL (day); more stringent requirements apply in Class B, C, D, and E. IFR flight plan requirements and alternate airport weather minimums are specified in §§91.169–91.185. §91.103 requires the PIC to become familiar with all available information concerning the flight, including weather reports, NOTAMs, fuel requirements, and known traffic delays.

Subpart D (Special Flight Operations) addresses operations that deviate from the general rules, including aerobatic flight (§91.303), formation flight (§91.111), and parachute operations (§91.307). §91.313 governs restricted-category aircraft; §91.319 covers experimental certificates. These provisions directly affect flight schools that operate tailwheel, aerobatic, or homebuilt training aircraft.

Subpart E (Maintenance, Preventive Maintenance, and Alterations) establishes the owner/operator's maintenance obligations. §91.403 makes the aircraft owner or operator responsible for maintaining airworthiness. §91.405 requires compliance with any applicable airworthiness directive within the time limits specified in the AD. §91.407 restricts flight after maintenance, preventive maintenance, or alteration until required inspections are complete and the aircraft is released to service. §91.409 mandates the annual inspection (performed by an IA) and the 100-hour inspection for aircraft operated for hire or flight instruction. §91.411 and §91.413 require altimeter/pitot-static system and ATC transponder inspections every 24 calendar months. §91.417 specifies maintenance record-keeping requirements: records must document current status of life-limited parts, time since last overhaul of all items required to be overhauled, current inspection status, current ADs including methods of compliance, and must be retained for the life of the aircraft (status records) or 1 year after the work was performed (maintenance records).

For flight schools, Part 91 creates a layered compliance environment. A Part 141 or Part 61 school operating training aircraft for hire is simultaneously subject to the maintenance inspection intervals of §91.409 — specifically the 100-hour inspection requirement that applies when aircraft are used for flight instruction for hire. The 100-hour limit is calendar-independent: it accumulates on Hobbs or tach time, and operating even one hour over the limit without a required inspection is an immediate airworthiness violation. Schools with busy fleets flying 60–80 hours per month may need to schedule 100-hour inspections less than 45 days apart, making tight maintenance scheduling essential to avoid grounding aircraft at operationally inconvenient times.

The §91.417 record-keeping requirements create a documentation obligation that persists across every maintenance event. Schools that cannot produce a complete, current AD compliance record or that have gaps in their logbooks during an FSDO inspection face potential certificate action. The interaction between §91.213 (inoperative equipment) and the Minimum Equipment List (if applicable) also requires instructors and dispatchers to evaluate every squawk before deciding whether a flight can legally depart — a judgment call that Part 91 assigns to the PIC but which training-focused operations must systematize to avoid inconsistent decisions.

Aviatize's maintenance control module tracks Hobbs and tach time against every recurring inspection interval mandated by Part 91 Subpart E. The 100-hour inspection clock is updated automatically as flight time is logged, and configurable warning thresholds — typically set at 90 hours — alert the maintenance team in advance so inspections can be scheduled without grounding aircraft mid-week. The platform also maintains a live AD compliance record for each aircraft, cross-referencing the airframe, engine, and avionics stack against the current AD list, so §91.403 and §91.405 obligations are visible rather than buried in paper logbooks.

For dispatch compliance under §91.409 and §91.213, Aviatize's booking engine checks each aircraft's current inspection status and open squawks before allowing a flight to be confirmed. An aircraft that has exceeded its 100-hour limit, has an overdue altimeter or transponder check under §91.411/§91.413, or carries an open MEL deferral that has expired cannot be booked — enforcement that replaces manual desk checks with automated pre-booking validation. Maintenance records stored in the platform satisfy §91.417 retention requirements and are exportable on demand for FSDO audits.