Part 135 refers to 14 CFR Part 135 — the US regulation governing commercial air taxi and commuter operations. A Part 135 Air Carrier Certificate issued by the FAA is the legal basis for any for-hire passenger or cargo flight outside scheduled airline operations (Part 121) or private corporate flight departments (Part 91).
A Part 135 certificate comes with Operations Specifications (OpSpecs) that define the authorised aircraft types, geographic area of operation, mission profiles (single-pilot IFR, two-pilot IFR, VFR-only, etc.), and any specific waivers or authorisations. OpSpecs are where a charter operator's real capability lives: a sophisticated buyer checks them before checking price.
Third-party safety ratings from ARGUS (Gold, Platinum, Platinum Elite) and Wyvern (Registered, Wingman) layer on top of Part 135. Corporate charter buyers, broker aggregators, and high-net-worth passengers often require a rating as a precondition to booking.
For marketing, Part 135 operators win direct bookings by surfacing the parts of the certificate buyers actually care about: aircraft type availability, specific mission authorisations (EMS, cargo, remote-area), ARGUS/Wyvern rating status, Safety Management System maturity, and dispatch response time. Pages that lead with jet photos and generic 'private charter' language underperform pages that lead with credentials.