# Airworthiness Directives; Fokker Model F28 Mark 1000 Through 4000 Series Airplanes
> **Rule** · Final rule. · Published 1998-03-23 · Effective 1998-04-27 · 63 FR 13775
## Document
- **Document number:** 98-7093
- **Category:** airworthiness
- **Manufacturer:** Fokker Model F28 Mark 1000 Through 4000 Series
- **Type:** Rule
- **Action:** Final rule.
- **Citation:** 63 FR 13775
- **Publication date:** 1998-03-23
- **Effective date:** 1998-04-27
- **FAA docket:** Docket No. 96-NM-176-AD
## Abstract

This amendment adopts a new airworthiness directive (AD), applicable to certain Fokker Model F28 Mark 1000 through 4000 series airplanes, that requires replacing certain flexible hydraulic hoses that connect to the UP-port of the actuator of each main landing gear (MLG) with certain new flexible hoses that have built-in restrictor check-valves. This amendment is prompted by results of tests, which indicate that, for airplanes on which restrictor check-valves are not installed, sudden movement of the actuator of the MLG, which could occur under extreme inward sideload conditions (such as touching down at a large crab angle), may pressurize the downlock-actuator and lift the MLG toggle-links. The actions specified by this AD are intended to prevent such pressurization of the downlock-actuator and consequent lifting of the toggle-links, which could result in collapse of the MLG and reduced controllability of the airplane during landing.

## Source
- [Federal Register document](https://www.federalregister.gov/documents/1998/03/23/98-7093/airworthiness-directives-fokker-model-f28-mark-1000-through-4000-series-airplanes)
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