Class 769 Flex Bi-mode Conversion Programme
UK (various operators including Northern Trains, Transport for Wales Rail) · 2017–2021 (conversion), 2020 (first service) · Not a single consolidated cost available. Conversion costs per unit not explicitly stated, but part of wider fleet modernization efforts.
The judgement call
Account-gated at launchThe project was initiated to address a shortage of diesel multiple units and provide a flexible solution for routes with partial electrification, demonstrating an innovative approach to fleet utilization. - The extensive engineering hours and involvement of original designers to compensate for missing drawings highlight the complexities of converting older rolling stock. - The voluntary application of standardized safety methods for risk evaluation, despite not being strictly required, underscores the commitment to safety in novel conversion projects. - The severe reliability issues and subsequent withdrawal of units by some operators (e.g., GWR) serve as a critical lesson in the challenges of complex conversions and the importance of thorough testing and validation before widespread deployment.
Key engineering challenges
Converting existing electric multiple units (Class 319) into bi-mode units by integrating diesel engines and alternators to power existing traction systems. - Ensuring seamless switchover between electric (AC/DC) and diesel modes, potentially while in motion. - Adapting the original vehicle structure to accommodate new powerpacks, including managing weight distribution, suspension, and fire safety. - Overcoming significant delays and reliability issues during testing and early service, leading to the units being dubbed "Britain's worst train" by some.
Project facts
- Client / owner
- Porterbrook (owner); Northern Trains; Transport for Wales Rail
- Lead contractor
- Brush Traction (conversion); Knorr-Bremse Rail Services (reliability improvements, re-branding)
- Lead designers
- Porterbrook; Brush Traction
- Project type
- refurbishment; vehicle/fleet programme
- Scale
- Converted from Class 319 EMUs; 4-car units; Max speed: 100 mph (161 km/h); Power output: 390 kW (520 hp) per engine (2 engines per unit)
- Disciplines
- Mechanical; Electrical; Systems; Software
- Standards & frameworks
- Standardised safety method for risk evaluation and assessment (voluntarily applied)
Sources: British Rail Class 769 - Wikipedia (https://en.wikipedia.org/wiki/British_Rail_Class_769) - Rail Engineer: Class 769 Flex (https://www.railengineer.co.uk/2018/09/17/class-769-flex/) - Rail Business UK: GWR fleet to shrink further as it abandons Class 769 introduction (https://www.railbusinessuk.com/traction-rolling-stock/2022/12/23/gwr-fleet-to-shrink-further-as-it-abandons-class-769-introduction/)