Title 14 CFR Part 135 is the federal regulatory framework governing air taxi, charter, and small commuter operations in the United States. It occupies the middle ground between the freewheeling flexibility of Part 91 and the highly structured world of Part 121 scheduled airlines. For any commercial pilot aspiring to fly professionally outside the major airline environment — corporate charter, on-demand air taxi, medevac, or small commuter routes — Part 135 is the rulebook that governs daily operations, crew qualifications, aircraft requirements, and passenger protection standards.
The Two Fundamental Categories
Part 135 divides operations into two principal categories, and the distinction matters because different rules apply to each.
Commuter Operations
A commuter operation uses aircraft with nine or fewer passenger seats (excluding pilot seats), conducting scheduled passenger-carrying operations with at least five round trips per week between two or more points. The scheduled, recurring nature of commuter flying subjects it to somewhat more structured requirements, including stricter instrument approach weather minimums at certain destinations.
On-Demand Operations
On-demand operations encompass everything that does not meet the commuter definition — single-engine air taxi flights, multi-engine turbine charter runs, cargo on-demand, medevac transports, and similar missions. Because these flights are irregular by nature, the regulatory framework addresses how operators must still ensure consistent safety standards without the predictability of a fixed schedule.
The Certificate and Operations Specifications
Before a single paying passenger boards, the company must hold a valid Part 135 air carrier certificate issued by the FAA. Obtaining that certificate requires demonstrating adequate management personnel, a safety program, an approved training program, suitable aircraft, and other resources. Once issued, the certificate is accompanied by Operations Specifications (OpSpecs) — FAA-approved documents that precisely define which aircraft, routes, areas of operation, and types of service the certificate holder is authorized to conduct.
OpSpecs are legally binding on the certificate holder and every crewmember operating under the certificate. If an aircraft type or a particular type of operation is not listed in the OpSpecs, it is simply not authorized — regardless of what the regulations might otherwise permit in the abstract. This is one of the most commonly tested concepts on the FAA Commercial Pilot Knowledge Test: the regulations set the outer boundary, but OpSpecs can be more restrictive, and the more restrictive document controls.
Pilot Qualification Requirements
Part 135 imposes experience minimums on top of the underlying certificate and rating requirements found in Part 61. These are additional prerequisites, not substitutes.
PIC Minimums — Single-Engine VFR
- 500 hours total flight time
- 100 hours of cross-country flight time
- 10 hours of night flight time
- 10 hours of instrument time (actual or simulated)
PIC Minimums — Multi-Engine IFR
- 1,200 hours total flight time
- 500 hours cross-country
- 100 hours of night flight
- 75 hours actual or simulated instrument time, of which at least 50 hours must be in actual instrument conditions
SIC Minimums
A second-in-command (SIC) must hold at least a commercial certificate with appropriate ratings and meet the instrument experience requirements specified in Part 135. For certain turbine-powered multi-engine operations, an SIC is required regardless of the aircraft's certificated single-pilot capability.
Additionally, before serving as PIC, a pilot must complete the certificate holder's approved initial ground and flight training, pass a Part 135 competency check in the specific make and model, and hold a current instrument proficiency check if IFR flights are to be conducted. Recurrent training and checking must occur at specified intervals — typically every 12 calendar months for the competency check.
Flight Time, Duty, and Rest Limitations
Fatigue is a well-documented cause of aviation accidents. Part 135 addresses this with specific limits, and the exam tests these numbers frequently.
- Annual flight time limit: Under 14 CFR 135.267, a pilot in scheduled operations may not fly more than 1,200 hours in any calendar year, with additional limits of 120 hours in any 30 consecutive days and 34 hours in any 7 consecutive days.
- Single-pilot 24-hour limit: No more than 8 flight hours in any 24 consecutive hours for single-pilot operations.
- Multi-crew 24-hour limit: No more than 10 flight hours in any 24 consecutive hours when a second crewmember is required.
- Minimum rest period: Before beginning flight duty, a pilot must receive at least 9 consecutive hours of rest in the preceding 24 hours. If a pilot does not receive that rest, the certificate holder must provide a rest period before flight.
- 500-hour limitation in any calendar quarter: Part 135.267 further caps flight time to help distribute fatigue risk across the year.
These limits interact with each other, and exam questions often describe a scenario and ask whether a flight is legal. Read carefully: the 8-versus-10 hour split depends on whether single-pilot or multi-crew operations are involved, not simply on aircraft size.
Weather Minimums and IFR Requirements
Part 135 weather minimums are generally more restrictive than basic Part 91 VFR and IFR standards, and they vary based on operation type and destination facilities.
For VFR flight, Part 135 prohibits passenger-carrying operations when the ceiling is below 1,000 feet or visibility is less than 3 statute miles for day operations, and the minimums are higher at night. These exceed the basic Part 91 VFR minimums in controlled airspace.
For IFR flight, Part 135 requires that a flight may not depart if the destination weather is forecast below the instrument approach minimums at the estimated time of arrival, unless an alternate airport is filed. The alternate airport weather requirements under Part 135 are more conservative than the standard Part 91 alternate rules. Specifically, when a destination does not have a standard instrument approach, no alternate is acceptable unless it has an approved approach and forecast weather above Part 135 alternate minimums.
For turbine-powered aircraft conducting IFR flight under Part 135, airborne weather radar or an approved weather avoidance system is required equipment. This is a hard equipment requirement — not just advisory guidance.
Aircraft and Equipment Requirements
Every aircraft operated under Part 135 must have an FAA-approved Airplane Flight Manual (AFM) that is current and on board. The aircraft must be maintained under an approved aircraft inspection program — operators cannot simply rely on the standard annual inspection used in Part 91 private operations. Approved inspection programs must be specifically authorized in the OpSpecs.
Emergency equipment requirements include items such as first aid kits, fire extinguishers, and survival equipment appropriate to the route being flown (over-water, polar, mountainous terrain). Passenger briefing cards and safety information meeting Part 135 standards are mandatory on every flight carrying passengers.
Common Test Traps
- Part 135 is not Part 121: Large transport-category scheduled airlines operate under Part 121, which carries its own — generally more stringent — rest and crew requirements. Mixing the two on an exam question is an easy way to lose points.
- Multi-engine PIC minimums are significantly higher: The 500-hour total time figure applies only to single-engine VFR operations. For multi-engine IFR, the requirement jumps to 1,200 hours total time. These are not interchangeable.
- OpSpecs restrict, never expand beyond, the regulations: A common distractor suggests that because the regulations permit something, a specific operator may do it. If the OpSpecs do not authorize it, the answer is no.
- Rest is consecutive hours, not cumulative: The 9-hour rest requirement means 9 uninterrupted hours, not 9 hours spread across a duty period.
- Scheduled vs. on-demand changes the applicable rule: Some questions describe an operation that could be either commuter or on-demand depending on frequency and seating. Identify the category first, then apply the correct rule.
Memory Aid
Use the "Three Cs" to frame any Part 135 legality question: Certificate (does the operator hold a valid Part 135 certificate?), Compliance (do the OpSpecs authorize this specific operation, aircraft, and route?), and Currency (are the pilot's qualifications, training, rest, and recency all current?). All three must be satisfied before a single revenue passenger boards. This is not an official FAA mnemonic, but it captures the three pillars examiners routinely test.