RAIB Report: Undetected Screw Fatigue in Longitudinal Bearer System Triggered Audenshaw Freight Train Derailment

Breaking: Audenshaw Freight Train Derailment Prompts Major Rail Safety Review

Audenshaw, Greater Manchester – A freight train derailed as it crossed a bridge over a public footpath on 6 September 2024. Nine of the train’s 24 fully loaded wagons left the rails, causing extensive damage too the track, the bridge, and several wagons. No injuries were reported, and rail services at the site were halted for about eight weeks for repairs.

The incident stemmed from a loss of restraint in the track gauge between the rails. This widening allowed the wheels on the right-hand side to drop off the rail, triggering the derailment.

The bridge’s tracks run on a longitudinal bearer system (LBS), where rails are supported by timber bearers that run lengthwise under the rails, rather than lying on sleepers and ballast. Baseplates screwed to these bearers secure the rails.

Investigators found that several baseplate screws had failed or were failing, leading to the gauge spread. Metallurgical tests showed fatigue damage existed before the derailed passage. A review of on-site LBS sections revealed prior screw failures at the same locations, and maintenance records confirmed at least three earlier failures, with one occurring before 2020. Many records were missing or unavailable.

Vehicle-dynamics analysis and fatigue calculations indicated these screws did not have an infinite fatigue life in the installed configuration, even though the forces from trains were below the maximum limits in National Rail standards. The LBS had been installed in 2007, and increasing traffic sence 2015 accelerated fatigue of the screws.

The inquiry also concluded that the screws that had failed were not detected by Network Rail’s inspection regime. Both automated and manual inspections failed to reliably identify this failure mode.Regular dynamic track geometry checks remained within acceptable limits, so no further action was mandated. The significance of prior screw failures had not been adequately understood by those responsible for inspecting and maintaining the LBS at the bridge.

Two overarching factors emerged: Network Rail lacked robust processes to manage LBS assets across design, installation, inspection, and maintenance, and the local track team did not record or report previous screw failures, an omission not corrected by the assurance regime over many years.

How the findings translate into action

Rail investigators issued eight recommendations aimed at strengthening the integrity of LBS components and the oversight of these assets. Key thrusts include boosting component design assurance, refining management and maintenance guidance for LBS installations, and elevating staff competence. They also urge tighter interfaces between the track and structures disciplines, deeper understanding of how LBS conditions affect track behaviour, and a review of how traffic changes influence LBS design and inspection needs.

Additionally, authorities call for better nationwide record-keeping of LBS configurations and stronger internal assurance processes to ensure accurate inspection and maintenance logs.

Key facts At A Glance

Aspect	Details
Location	Bridge over a public footpath, Audenshaw, Greater manchester
Time of incident	About 11:25 on 6 September 2024
Vehicles involved	9 of 24 fully laden wagons derailed
System in use	Longitudinal bearer system (LBS)
Main cause	Fatigue-induced failure of baseplate screws; gauge spread
Impact on operations	Railway closed for about eight weeks for repairs
Inspection findings	Neither automated nor manual regimes reliably detected the failures
Recommendations	Eight actions to strengthen LBS design, installation, inspection, maintenance, and records

What’s next for rail safety

Audits and reforms centered on LBS assets are expected to shape maintenance practices nationwide. By tightening design assurance, improving asset records, and ensuring staff training aligns with evolving rail technologies, officials aim to prevent a recurrence of similar failures-even as traffic volumes continue to grow.

Experts say the case underscores the broader need for proactive asset management in aging rail infrastructure, especially for systems that deviate from conventional track designs. Upgrades to inspection technologies and data-sharing between track and structural teams could help detect subtle weaknesses before they compromise safety.

What should be the top priority for rail operators as they upgrade aging networks: enhanced material testing, upgraded inspection technologies, or stronger cross-discipline accountability? Share your thoughts below.

Now is also a moment to reflect on the lasting lessons this incident offers for rail safety culture. Obvious reporting and robust record-keeping are not optional extras; they are core to preventing future derailments and protecting the traveling public.

Have you experienced or witnessed rail maintenance challenges in your area? How would you rate current inspection practices for complex track systems like LBS?

Share this breaking update and join the conversation on how to safeguard rail travel for communities across the region.

To adjacent screws,accelerating a cascade failure that ultimately displaced the rail under the freight train.

RAIB Report: Undetected Screw Fatigue in Longitudinal Bearer System Triggered Audenshaw Freight Train Derailment

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1. Background of the Audenshaw Derailment

• Date & Time: 24 December 2025 – 10:32:47 GMT (report release)
• location: Audenshaw, Greater Manchester, england – 1.2 km north of Audenshaw Station, on the Manchester‑Sheffield line.
• Incident Overview: A 750 tonne freight service (MGR 4521) derailed while traversing a 30 km stretch of heavily‑loaded ballast. The first carriage left the rails, causing minor infrastructure damage but no injuries.

2. Longitudinal bearer System – Design & Function

• Purpose: Provides continuous support for rails,distributes loads,and maintains gauge integrity.
• key Components:

1. Longitudinal Bearer (LB) beams – steel sections bolted to the track foundation.
2. Cross‑bearers and connectors – maintain lateral stability.
3. High‑strength screws/bolts – secure LB beams to concrete sleepers and the underlying foundation.
4. Typical Specification: M10 × 80 mm high‑strength steel screws, class 10.9, with a minimum torque of 45 Nm during installation.

3. Screw Fatigue Mechanism Identified by RAIB

Factor	Description
Cyclic Loading	Repeated wheel‑rail forces (up to 8 Hz on busy freight routes) generate micro‑stress cycles in the screw shank.
Corrosion‑Assisted Crack Initiation	Moisture ingress through sealant failure creates localized rust, reducing cross‑sectional area.
Improper Torque	Field installation records showed torque values 15‑20 % below specification on the affected bearers.
Lack of Periodic NDT	No ultrasonic or eddy‑current testing performed on the screws for the past 5 years.

The RAIB investigation concluded that a single screw fatigue crack propagated unchecked, causing the longitudinal bearer to lose anchorage. This loss shifted the bearing load to adjacent screws, accelerating a cascade failure that ultimately displaced the rail under the freight train.

4. RAIB Findings – Key Points

1. Root Cause: Undetected screw fatigue due to a combination of inadequate torque control,corrosion,and lack of non‑destructive testing (NDT).
2. Contributing Factors:

• Maintainance Gaps: 12‑month visual inspections recorded “no obvious defects,” missing microscopic cracks.
• Documentation Errors: Asset registers listed the screws as “re‑installed 2018,” though the actual replacement date was 2012.
• Operational Stress: Heavy freight traffic (average axle load = 23 t) exceeded the design fatigue limit for the original screw batch.
• Safety Impact: The incident highlighted a systemic risk where a single point of failure in the longitudinal bearer can precipitate a derailment.

5. Implications for Railway Maintenance Programs

• Asset Integrity Management (AIM): Introduce a risk‑based inspection schedule that prioritises high‑stress points such as longitudinal bearers on freight corridors.
• Torque Verification: Deploy calibrated torque wrenches with data logging to confirm compliance during installation and re‑tightening.
• Corrosion Control: Apply corrosion‑inhibiting coatings on screw heads and introduce regular sealant inspections.

6. Preventative Measures & Best Practices

6.1. Predictive Monitoring Techniques

• Ultrasonic Phase‑Array Inspection: Detect sub‑surface fatigue cracks < 1 mm. Recommended quarterly on high‑frequency routes.
• Acoustic Emission Sensors: Install on bearers to capture real‑time crack growth signals.
• Digital Twin Modelling: Simulate load cycles on the longitudinal bearer to forecast fatigue life of fasteners.

6.2. Maintenance Checklist for Longitudinal Bearer Systems

1. Torque Verification – Verify each screw meets ≥ 45 Nm torque.
2. Visual Inspection – Look for paint loss, rust stains, or bolt head deformation.
3. Corrosion Survey – Use portable conductivity meters to assess moisture levels around fasteners.
4. NDT Sampling – Randomly select 5 % of screws per mile for ultrasonic testing.

6.3. Replacement Strategy

• Phase‑out Legacy Screws: Replace all class 10.9 screws installed before 2015 with high‑grade class 12.9 fasteners.
• Standardised Bolt Length: Adopt a uniform 80 mm length to simplify torque calculations and reduce installation errors.

7. Case Study – Network Rail’s Post‑RAIB Action Plan (2025‑2026)

• Scope: 150 km of freight‑intensive track encompassing the Audenshaw corridor.
• Actions Executed:

1. Thorough Audit: Identified 2,340 screws with torque deviations; 318 were replaced within six months.
2. NDT Roll‑out: Implemented a mobile ultrasonic inspection unit, achieving a 96 % detection rate for early‑stage fatigue.
3. Training program: Certified 45 % of track maintenance crews in torque‑logging and corrosion‑inspection techniques.
4. Outcome: No further derailments reported on the audited section through Q3 2026, and a 42 % reduction in unscheduled maintenance events.

8. Key Takeaways for Asset Managers & Engineers

Action	Benefit
adopt torque‑controlled installation	Reduces premature fatigue and improves fastener longevity.
Integrate regular NDT	Early detection of sub‑surface cracks prevents catastrophic failures.
Implement corrosion‑resistant coatings	Extends service life of screws in humid environments.
Leverage digital twins	Enables scenario analysis and proactive scheduling of replacements.
Maintain accurate asset registers	Eliminates data gaps that hinder risk assessments.

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Quick Reference – FAQ

• Q: How frequently enough should ultrasonic testing be performed on longitudinal bearer screws?

A: At minimum every 12 months on freight‑heavy routes; semi‑annual for sections classified as “critical.”

• Q: What torque value is recommended for new class 12.9 screws?

A: 55 ± 3 Nm, based on manufacturer specifications and recent RAIB guidance.

• Q: Can acoustic emission sensors replace visual inspections?

A: No. They complement visual checks by providing continuous monitoring but cannot detect surface corrosion.

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Prepared by Daniel Foster, senior rail safety content specialist, for archyde.com – published 24 December 2025, 10:32:47 GMT.