# STC ST521SO

- Type: Supplemental type certificate
- Status: Current, Amended
- Holder: Lockheed Martin Aeronautics Company, United States
- Description: Increase in maximum landing weight to 135,000 pounds and maximum zero fuel weight to 128,790 pounds with pylon tanks on and 127,000 pounds with pylon tanks off.
- Status date: August 24, 1983
- Product: Aircraft, Large Multi-Engine
- Certification basis: Part 21
- Data sheets: [TCDS A1SO](https://openairdocs.org/tcds/A1SO)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/747A935B484DC36E85256CC300036064.0001
- DRS record last changed: December 6, 2025
- Page: https://openairdocs.org/stc/ST521SO

## ADs that name it (0)

None.

## Approved models (2)

- Lockheed Aircraft Corporation 382 ([TCDS A1SO](https://openairdocs.org/tcds/A1SO))
- Lockheed Aircraft Corporation 382E ([TCDS A1SO](https://openairdocs.org/tcds/A1SO))

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