# Proposed AD 98-NM-252-AD: Boeing Model 747-400 Series Airplanes

- Type: Proposed airworthiness directive (not in force)
- Status: Became AD 2000-02-33
- Action: Notice of proposed rulemaking (NPRM).
- Published: June 22, 1999, 64 FR 33229
- Comments due: August 6, 1999
- Became: [AD 2000-02-33](https://openairdocs.org/ad/2000-02-33)
- Docket: 98-NM-252-AD
- FR document: 99-15774
- Official PDF: https://openairdocs.org/files/sha256/95/b1/95b1d0b20f66398a213396ba13aa6c4d646f7b5d3a621d85a7d6246bb36c5c10 (from https://www.govinfo.gov/content/pkg/FR-1999-06-22/pdf/99-15774.pdf)
- Federal Register: https://www.federalregister.gov/documents/1999/06/22/99-15774/airworthiness-directives-boeing-model-747-400-series-airplanes
- Page: https://openairdocs.org/proposed/98-NM-252-AD

## Summary

This document proposes the supersedure of an existing airworthiness directive (AD), applicable to all Boeing Model 747-400 series airplanes, that currently requires various inspections and functional tests to detect discrepancies of the thrust reverser control and indication system, and correction of any discrepancy found. This action would reduce the repetitive interval for one certain functional test. This proposal is prompted by reports indicating that several center drive units (CDU) were returned to the manufacturer of the CDU's because of low holding torque of the CDU cone brake. The actions specified by the proposed AD are intended to ensure the integrity of the fail safe features of the thrust reverser system by preventing possible failure modes in the thrust reverser control system that can result in inadvertent deployment of a thrust reverser during flight.

## Notices in this docket

- Jun 22, 1999: Notice of proposed rulemaking (NPRM). (first notice), FR document 99-15774, comments due Aug 6, 1999 (https://www.federalregister.gov/documents/1999/06/22/99-15774/airworthiness-directives-boeing-model-747-400-series-airplanes)

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