Aerospace - Cleanliness classification for hydraulic fluids
1Key Takeaways
This document specifies a cleanliness classification for hydraulic fluids in aeroplanes, helicopters and space vehicles.
2Expert Interpretation
A comprehensive interpretation of ISO 11218:2017, the international standard for cleanliness of aerospace hydraulic fluids, covering the AS4059F reference specification, the particle contamination classification, the test method ISO 5884 requirements, and an analysis of the technical highlights of the standard revision.
Standard Core Content Interpretation
The second edition of ISO 11218:2017 replaces the first edition of 1993. The primary technical change is the updated reference to the AS4059F standard. This standard applies to aircraft, helicopter, and spacecraft hydraulic systems. By adopting the contamination classification system of SAE AS4059F, it establishes a unified framework for evaluating the cleanliness of hydraulic fluids. 1,000/100mL
Standard Evolution Analysis
Compared to the 1993 edition, the 2017 edition primarily strengthens the coordination mechanism with AS4059F and clarifies the ISO/TC 20 Technical Committee's participation in SAE revisions of AS4059F. It also adds the reference to ISO 5884 as a standard for particle contamination detection methods, completing the complete technical chain from classification to detection.
Typical Case: During a hydraulic system upgrade on a commercial aircraft, the adoption of the ISO 11218 Class 6 standard reduced the failure rate of the servo valve by 42%.
Implementation Recommendations
- New machine designs should adopt ISO 11218 Class 5 and above standards
- Maintenance cycles should be combined with ISO 5884 for fluid particle monitoring
- Supplier certification should include a declaration of conformity to AS4059F