What Is the Difference Between Part 135 and Part 91?

The legal hinge is operational control. Under Part 135, a certificated air carrier holds operational control of the flight and carries the corresponding safety and legal responsibility: it decides whether the flight goes, who crews it, and to what standard. Under Part 91, the aircraft owner or operator retains that control and is flying for their own purposes, not for hire. Everything else follows from that distinction.

Part 135 imposes materially higher requirements. Certificate holders must maintain a management structure that typically includes a director of operations, chief pilot and director of maintenance. Pilot duty and rest limits, flight and duty recordkeeping, dispatch releases, weather minimums, maintenance intervals and passenger-handling procedures are all more restrictive than the Part 91 equivalents, and are subject to ongoing FAA surveillance of the certificate itself.

This is where the illegal-charter problem lives. An operator that puts paying passengers on a Part 91 flight is offering a cheaper product because it has skipped the certificate and the compliance overhead that goes with it. The consequence for the passenger is not theoretical: insurance on the aircraft may not cover commercial carriage, meaning a claim after an accident can be denied outright. The FAA and NTSB have both flagged illegal charter as a persistent safety problem.

Ask any broker or operator for the Part 135 certificate holder's name and certificate number, and confirm the specific aircraft is listed on that certificate's operations specifications. A legitimate operator answers this immediately and in writing. Related to this: because Part 135 flights are commercial transportation, the amounts you pay are generally subject to the 7.5 percent federal excise tax plus the per-passenger domestic segment fee — a tax posture that itself signals the flight is being conducted correctly.