EASA SIB 2007-34: Use of Non-Approved Gearbox Oil in TAE 125 series engines

What to do

Operators must verify before the next flight that only approved gearbox oils are used in TAE 125-01 and 125-02 engines. If the use of approved oil cannot be confirmed, the gearbox must be removed and inspected within 50 flight hours, at the next 100 flight hour inspection, or within three months, whichever occurs first, following Thielert's maintenance instructions. National Aviation Authorities are recommended to adopt these measures as mandatory under their regulatory authority.

Summary

EASA Safety Information Notice No. 2007-34 addresses the use of non-approved gearbox oils in Thielert Aircraft Engines (TAE) 125-01 and 125-02 series engines, which are installed on various single- and twin-engine aircraft certified under US, Canadian, and European Part 23 airworthiness standards. The notice highlights that only Shell EP 75W-90 API GL-4 or Shell Spirax GSX 75W-80 oils are approved for these gearboxes. Using non-approved oils, especially GL-5 types, can cause gearbox damage and propeller control failures, potentially leading to engine overspeed or in-flight shutdown.

What changed

This Safety Information Notice introduces a formal warning against the use of non-approved gearbox oils in TAE 125 series engines and recommends specific inspection and maintenance actions. It clarifies that the unsafe condition arises from maintenance practices rather than design flaws, and thus EASA will not issue an Airworthiness Directive but encourages National Aviation Authorities to enforce mandatory measures. The document also references Thielert's Service Center Circular No. 31a/2007, which emphasizes exclusive use of approved fluids to maintain warranty and safety.

Why it matters

For aviation operators, maintenance organizations, and compliance teams, this notice underscores the critical importance of adhering to approved lubricant specifications to prevent serious mechanical failures and safety risks. Non-compliance can lead to costly repairs, warranty voidance, and increased risk of in-flight engine shutdowns. Ensuring correct gearbox oil usage is essential for maintaining engine reliability and regulatory compliance.