# Proposed AD 98-NM-383-AD: Boeing Model 737 Series Airplanes

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 99-11-05
- Action: Notice of proposed rulemaking (NPRM).
- Published: January 13, 1999, 64 FR 2161
- Comments due: February 12, 1999
- Became: [AD 99-11-05](https://openairdocs.org/ad/99-11-05)
- Docket: 98-NM-383-AD
- FR document: 99-682
- Official PDF: https://openairdocs.org/files/sha256/ae/3a/ae3a6c30858a1747e6adee42d052c30f29572b1861064b2f34b26ba599969091 (from https://www.govinfo.gov/content/pkg/FR-1999-01-13/pdf/99-682.pdf)
- Federal Register: https://www.federalregister.gov/documents/1999/01/13/99-682/airworthiness-directives-boeing-model-737-series-airplanes
- Page: https://openairdocs.org/proposed/98-NM-383-AD

## Summary

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Boeing Model 737 series airplanes. This proposal would require repetitive displacement tests of the secondary slide in the dual concentric servo valve of the power control unit (PCU) for the rudder, and replacement of the valve assembly with a modified valve assembly, if necessary. This proposal is prompted by reports of cracking found in PCU secondary servo valve slides. The actions specified by the proposed AD are intended to prevent failure of the secondary slide and consequent rudder hardover and reduced controllability of the airplane.

## Notices in this docket

- Jan 13, 1999: Notice of proposed rulemaking (NPRM). (first notice), FR document 99-682, comments due Feb 12, 1999 (https://www.federalregister.gov/documents/1999/01/13/99-682/airworthiness-directives-boeing-model-737-series-airplanes)

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