EASA SIB 2018-04R2: Environmentally Assisted Cracking in certain Aluminium Alloys

What to do

Affected organizations should identify components made from EAC-sensitive aluminium alloys and assess their susceptibility and criticality to this cracking phenomenon. They are encouraged to report evaluation results to EASA and coordinate with aluminium alloy producers and design approval holders. The bulletin provides a generic test method for susceptibility assessment, which should be followed carefully to ensure valid results.

Summary

EASA Safety Information Bulletin 2018-04R2 addresses environmentally assisted cracking (EAC) in certain new generation 7xxx series aluminium alloys used in aviation structures. The bulletin highlights susceptibility of alloys such as 7037, 7040, 7055, 7085, 7099, 7140, and 7449 to hydrogen embrittlement cracking under specific environmental and stress conditions. This issue affects type certificate holders, manufacturers, and maintenance organizations involved with aluminium alloy components.

What changed

This revision updates the previous SIB 2018-04R1 by adding aluminium alloy 7140 in T7451 temper and providing further information on its behavior. It also introduces a generic test method to identify material susceptibility to this form of EAC. The bulletin clarifies that the safety concern does not currently warrant mandatory Airworthiness Directive action.

Why it matters

Understanding and detecting EAC in susceptible aluminium alloys is critical to maintaining structural integrity and preventing brittle fractures in aircraft components. Aviation professionals must be aware that standard stress corrosion cracking tests may not detect this form of cracking, which is driven by hydrogen embrittlement and ageing. Early identification and evaluation help operators and maintenance teams mitigate risks and avoid unexpected failures.