SH505GL
Installation of modified tail rotor gearbox using original installation hardware and components. Held by Helicopters, INC, which holds 6 approved modifications in all. Last revised February 20, 1981. System: rotorcraft systems.
What it applies to
What an approved modification is
A supplemental type certificate is the FAA's approval of a change to a certified design: a new engine or propeller, avionics, an autopilot, floats, a parachute, a larger fuel tank, an ice-protection kit. The company holding it may sell the kit and the paperwork to owners of the listed models; the modification then becomes part of that aircraft's record. The FAA's list says what was approved and for which models, not how many aircraft carry it.
Source: FAA supplemental type certificates (Dynamic Regulatory System). Register counts from the FAA register of October 21, 2026.