# STC SA355SO

- Type: Supplemental type certificate
- Status: Current, Issued
- Holder: Southern Airways Inc, United States
- Description: Whittaker 2L333021 NLG hydraulic pressure reducer valve replaced with Hydraulics Research42028180-001 valve.
- Status date: January 1, 1960
- Product: Aircraft, Large Multi-Engine
- Certification basis: Part 21
- Data sheets: [TCDS 1A7](https://openairdocs.org/tcds/1A7)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/A030DD20DE3B1C15862570CF005552A7.0001
- DRS record last changed: December 6, 2025
- Page: https://openairdocs.org/stc/SA355SO

## ADs that name it (0)

None.

## Approved models (1)

- Martin-Marietta Corporation 404 ([TCDS 1A7](https://openairdocs.org/tcds/1A7))

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From OpenAirDocs.org, an independent open copy of FAA and NTSB data. Only the Federal Register edition on govinfo.gov is the official legal text of an AD.