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Trent 700 Fan Case Corrosion: Detailed Inspection and Repair Guidance

Applicability

This guidance applies to corrosion observed at the 6 o’clock position, just behind the A1 flange and forward of the Kevlar wrap on Rolls-Royce Trent 700 engines. This location is structurally sensitive due to its proximity to containment-critical zones and composite wrap interfaces.

Engineering Context

Corrosion in this region typically arises from environmental exposure, moisture ingress, and chemical residue accumulation during extended on-wing operation. The fan case structure in this zone is subject to vibratory loads and thermal cycling, which can exacerbate surface degradation. Minor pitting and discolouration have been observed in recent inspections, with some cases requiring Technical Variance assessment for continued operation.

Inspection Protocols

On-Wing Inspection

  • Access via borescope or visual inspection through fan case ports.
  • Document corrosion location using clock position and frame station references.
  • Measure pitting depth and area using calibrated depth gauges or laser profilometry.
  • Capture high-resolution images for disposition review.

In-Shop Inspection

  • Remove fan case and Kevlar wrap for full exposure.
  • Conduct NDT using eddy current and ultrasonic methods.
  • Perform metallurgical sampling if corrosion depth exceeds 0.3 mm.
  • Inspect adjacent components (e.g., A1 flange, Kevlar interface) for secondary damage.

Repair Schemes

  • FRS3253: Minor corrosion blend and surface reconditioning. Applicable for pitting <0.3 mm.
  • TI2010-007: Material build-up and re-machining for deeper corrosion. Requires dimensional restoration and post-repair NDT.
  • SB 72-AF123: Rolls-Royce bulletin covering corrosion limits and blend criteria.
  • Airbus A330 AMM 72-00-00: Defines allowable damage and repair thresholds for fan case components.

Compliance and Safety

  • Repairs must maintain containment integrity and comply with FAA AC 43-4B and EASA Part 145.
  • Post-repair inspection must be signed off by a certified Level 3 inspector.
  • All findings must be recorded in the Continuing Airworthiness Record.
  • If corrosion is deemed non-conforming, a Technical Variance must be requested.

Operational Impact

  • Minor corrosion may be deferred under MEL with restrictions on thrust setting, altitude, and ETOPS limits.
  • Ferry flights may be permitted with engineering approval and documented risk assessment.
  • Trend monitoring (e.g., EGT margin loss) should be reviewed to assess downstream performance impact.

Tooling and Logistics

  • MRT dispatch requires Kevlar wrap inspection tooling, fan case blend kit, and calibrated depth gauges.
  • Repair kits must include approved materials, curing agents, and blend templates.
  • Removed components must be shipped with RMA documentation and hazardous declarations.

Technical References

  • TrentXWB CFG Digital Exhibition - COS Workshop 13Oct22: Case summary and corrosion disposition guidance.
  • Trent700_Corrosion_Inspection_Guide: Current working document.
  • SCC Service Transformation October 2025: Inspection feedback and clip removal criteria.
  • [EXTERNAL] RR - SSC Workshop Journeys: SCC case handling and customer journey context.
  • Marc Jones: Example airline queries and disposition prompts.
  • For further technical clarification, contact Grant Readings or refer to the internal engineering bulletin EB-TR700-2025-09.
Keywords: remplacement, repair guidance, corruption, repairs, corruption protocols, surface degradation, technical variance, treat 700

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