Definition
14 CFR Part 135 covers commercial air carrier operations that fall below the scope of Part 121 — primarily aircraft with 9 or fewer passenger seats or less than 7,500 lb payload, and commuter operations in aircraft with 10–30 passenger seats not meeting Part 121's large-aircraft thresholds. The regulation draws a fundamental distinction between single-pilot IFR operations (which face the most restrictive equipment and qualification requirements) and multi-crew operations. §135.1 defines four operational categories: commuter operations (scheduled service on routes of 70 statute miles or fewer), on-demand operations, all-cargo operations, and certain fractional ownership operations.
Pilot qualification under Part 135 is substantially higher than Part 91. §135.241 requires all PIC candidates for multi-engine turbine-powered aircraft or pressurized aircraft with a service ceiling above 25,000 ft MSL to hold an ATP certificate. For other aircraft, the PIC must hold at least a commercial certificate with an instrument rating. §135.243 establishes a minimum of 500 hours total time (200 hours cross-country, 100 hours at night, 75 hours actual or simulated instrument time) for PIC eligibility in a Part 135 IFR operation. These minimums are substantially above the commercial certificate's underlying FAR minimums and are checked at initial hire and documented in the operator's training records.
Initial and recurrent training and checking requirements are set out in §§135.293–135.301. §135.293 requires initial and annual recurrent ground and flight checks for all crewmembers; the check must cover emergency procedures, handling of hazardous weather, and other operator-specific items. §135.297 requires an annual instrument proficiency check in each aircraft type flown. §135.299 requires each PIC to pass a line check — an observation of actual line operations — at least every 12 calendar months. These checks may be administered by a check airman or, for operators with approved training programs, at a Part 142 training center.
Maintenance program requirements under §135.411 vary significantly by operation. Single-engine aircraft used in on-demand operations may use Part 91's standard inspection rules (§91.409 annual and 100-hour). Multi-engine aircraft used in on-demand operations must use an Approved Aircraft Inspection Program (AAIP) developed by the operator and approved by the FAA. Commuter category aircraft (10 or more passenger seats) must use a full Continuous Airworthiness Maintenance Program (CAMP) comparable to Part 121's §121.367 program. This creates a tiered maintenance compliance structure where the size and schedule of the operation determines which maintenance framework applies.
Flight and duty time limits under Part 135 Subpart F differ significantly from Part 121. §135.265 limits scheduled operations to 1,200 hours flight time in any 12-calendar-month period. On-demand operations under §135.267 set a 500-hour limit per 100 consecutive days. Rest requirements in §135.263 mandate a minimum of 10 consecutive hours rest before any flight time period. Split rest provisions and the 8-in-24 rule are defined in §135.263(c). Unlike Part 121's 2011 fatigue rule, Part 135 flight-duty regulations have not been comprehensively modernized, and NTSB safety recommendations have repeatedly flagged this gap.
Why It Matters for Flight Schools
Flight schools, ATOs, and aviation academies interact with Part 135 in two distinct ways. First, many schools that offer instrument, commercial, or multi-engine training also hold Part 135 certificates to operate charter flights — creating a combined training/charter operation with overlapping regulatory obligations. In these environments, the same aircraft and the same instructors may switch between Part 91 training operations (governed by Part 141 or Part 61) and Part 135 charter flights within the same day, requiring careful delineation of which set of rules applies to each flight leg and which training records, duty times, and check currency standards govern each operation.
Second, for schools that train pilots toward Part 135 careers — particularly HEMS operators and corporate charter providers — the §135.241 ATP/commercial qualification minimums and the §135.293/135.297/135.299 initial and recurrent check requirements define the competency milestones the training program must target. HEMS operations under Part 135 carry additional operational control requirements (§135.601–135.621) specific to helicopter EMS, including operational control centers, risk assessment systems, and adverse condition protocols that go beyond standard Part 135 requirements.
How Aviatize Handles This
Aviatize's compliance and auditing module tracks the Part 135 crewmember qualification matrix — ATP or commercial certificate level, multi-engine time, IFR time, and total time — against §135.241 and §135.243 minimums for each pilot. When a new charter flight is being rostered, the system validates that the assigned PIC meets qualification minimums for the specific aircraft and operation type (IFR single-engine, multi-engine pressurized above FL250, etc.) before the assignment is confirmed, preventing an unqualified pilot from being placed in command of a Part 135 flight.
Recurrent check calendars for §135.293 ground and flight checks, §135.297 instrument proficiency checks, and §135.299 line checks are maintained per crewmember and per aircraft type, with automated alerts at configurable lead times before expiry. For combined ATO/Part 135 operators, Aviatize's multi-operation architecture maintains separate training records for the ATO and the operating certificate, ensuring that a §135.299 line check completion and an ATO stage-check sign-off are recorded in the correct regulatory context rather than mixed in a single undifferentiated record.