# STC SA2021SO

- Type: Supplemental type certificate
- Status: Current, Issued
- Holder: AlliedSignal Commercial Avionics Systems, United States
- Description: Installation of Allied/Bendix microwave landing system MLS-21.
- Status date: December 5, 1986
- Product: Aircraft, Large Multi-Engine
- Certification basis: Part 21
- Data sheets: [TCDS A3WE](https://openairdocs.org/tcds/A3WE)
- FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/23527F9E713BEF0F85256CC10083D551.0001
- DRS record last changed: December 5, 2025
- Page: https://openairdocs.org/stc/SA2021SO

## ADs that name it (0)

None.

## Approved models (3)

- The Boeing Company 727 ([TCDS A3WE](https://openairdocs.org/tcds/A3WE))
- The Boeing Company 727-100 Series ([TCDS A3WE](https://openairdocs.org/tcds/A3WE))
- The Boeing Company 727-200 Series ([TCDS A3WE](https://openairdocs.org/tcds/A3WE))

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