Engine Strut Structure / Thermal Switch - Inspection
- Published
- Effective
AI-generated summary of the official EASA document. Verify against the PDF before acting.
What to do
Affected operators must perform a general visual inspection for heat damage on the engine strut structure and conduct repetitive thermal switch temperature and continuity tests within the specified compliance times, with the AD becoming effective on January 13, 2026. Model 757-300 operators must replace the precooler at intervals not exceeding 45,000 total precooler flight hours. Any on-condition repairs or replacements identified during inspections and tests must be completed promptly according to the AD requirements.
Summary
The document titled "Engine Strut Structure / Thermal Switch - Inspection" is a final rule airworthiness directive (AD 2025-23-03) issued by the Federal Aviation Administration (FAA) affecting certain Boeing Company Model 757 airplanes. It addresses issues related to precooler failures and latent failures of overheat detection thermal switches that could cause heat damage to the engine strut structure. The AD mandates inspections, tests, and replacements to ensure continued airworthiness and safety.
What changed
This new airworthiness directive introduces mandatory inspections for heat damage on the engine strut structure, repetitive thermal switch temperature and ground wire tests, and precooler replacements specifically for Model 757-300 airplanes. It also requires on-condition actions such as repairs or replacements if damage or failures are detected. The AD clarifies compliance requirements and responds to stakeholder comments without changing the original proposed measures.
Why it matters
This AD is critical for aviation professionals because it addresses a latent failure mode that could lead to severe thermal damage and potential separation of the engine strut-to-wing box connection, posing a significant safety risk. Operators, maintenance, and compliance teams must ensure timely inspections and tests to detect and mitigate these risks. The directive ensures that maintenance programs include these specific actions to prevent prolonged heat exposure and maintain structural integrity.
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