SA4-591
Increased maximum weight capacity of bow compartment. Held by Alaska Coastal Airlines, which holds 4 approved modifications in all. Last revised July 17, 2008. System: other and general.
What it applies to
- Kind of product
- Aircraft
- Design holder
- Grumman American Aviation Corporation; Grumman American Aviation Corporation
- Models
- G-21A, G-21
- Type certificates
- 654, 654
- On this site
- Grumman G-21 35 registered
- The FAA's record
- On the FAA's site
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 19, 2026.