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Engineering Change

Engineering change services include:

  • Fleet Modifications

  • Fleet Enhansment Projects

  • Obsolesance Soloutions

  • Rolling Stock Repairs

  • Risk Assessment (HAZID & Close Out)


  • Component Life Cycle Studies.

If we question the primary role of a train it is to safely transport people or goods from point A to point B. A secondary role is for it to depart and arrive at its destination on-time. It really is that simple!

Any change made to rolling stock has the potential to introduce an increased risk of safety, reliability and/or performance issues - these have considerable impact on the trains primary and secondary roles. The engineering change process is designed to highlight all credible risks associated with the change and ensure each risk is controlled to reduce it to as low as reasonably practical (ALARP). At its core the engineering change process is a highly detailed risk assessment.

In addition to safety, reliability and performance the engineering change process should also consider how the change effects train maintenance, train operation, compliance to applicable standards, compatibility with the infrastructure, spare parts, cleaning and the environmental impact to name a few. Maintenance documentation, train crew manuals, drawings may need to be amended to reflect the change. Procedures will need to be written to ensure the trains are changed correctly, safely and to the required standard. In some cases train crew or maintenance staff training may be required. Finally the implementation of the change is considered as other factors may affect how the change is implemented across the fleet.

Although the same engineering change process (as defined in the relevant Safety Management System) is followed for each change; there are an infinite amount of elements that can be considered, this results in a bespoke engineering change pack for each change. Depending on the significance of the change (i.e. the principle risk associated with the change) this change pack is presented to a variety of stakeholders for their review and approval. Once approved the change can be implemented in-line with the information contained in the change pack.

RIS-2700-RST Rail Industry Standard for Verification of Conformity of Engineering Change and ATOC/ACOP/EC/01006 Approved Code of Practice - Management of Rail Vehicle Engineering Change both are high-level, cross industry documents that set out processes which can be adopted by organisations that are undertaking engineering change projects. However, the proposer and assessment party (or parties) are still human and as such are susceptible to a multitude of weaknesses. The approved Safety Management System (SMS) should be designed in such a way that all human factors risks are reduced to as low as reasonably practical but it is impossible to eliminate.

As with anything, when carrying out the engineering change process the more experience the better. In an ideal world this experience would consist of fleet/system specific knowledge and familiarity with the engineering change process. It's also worth noting that a level of independence can proof highly beneficial; hence the reason it is mandatory for substantial engineering change projects.

Trevally Engineering has a lot of experience when it comes to engineering change. Lead Engineer, Andrew is very familiar with the process and has completed a number of engineering change projects for a variety of different fleet types over the last 10 years. Andrew has significant experience when it comes to writing change packs and has also reviewed hundreds of engineering change packs on behalf of clients.

Case Studies

Control Relay Replacement

The customer was experiencing on-going reliability issues with a range of Diesel Multiple Unit (DMU) train control relays; the scope of the project was to source modern alternatives in order to improve fleet reliability.


The customer had indicated their preferred relay type however the necessary approvals were required in order to prove the chosen relay for each application. The new relays were successfully proven for each application and were subsequently introduced under a fleet change-out program; ultimately improving system performance and overall fleet reliability.

Mk1 WSP Rack Repairs & Modifications

The customer informed that their overhauler had reported a number of obsolescence issues with the Mk1 Wheel Slip/Slide Protection (WSP) equipment. Including quarter turn fasteners, module guides, electrical sockets and wheel wear compensation potentiometers. The overhauler had begun to research suitable alternatives however Trevally Engineering were required to carry out the necessary approval work required in order to prove that the alternative solutions met industry standards and were suitable for the application


Trevally Engineering worked closely with the overhauler, visiting their workshop, to ensure each solution was fully understood, researched further, finally developed, proven 'fit-for-purpose' and approved via the customers engineering change process.

Repair and modification instructions were also written to standardise the repair/modification work for the rest of the supply chain.

Brake Control Unit (BCU/CCU) - Overhaul

The customer informed that a modern like-for-like Brake Control Unit (A.K.A. Code Conversion Unit) had been introduced onto two very similar train fleets, as the original units had become unreliable and were obsolete. The customer advised that both train fleets would be undergoing overhaul in the near future and that part of the scope was to overhaul the BCU's/CCU's. However, the new BCU's/CCU's had only recently been fitted so it wouldn't be commercially viable to overhaul them so soon.

Trevally Engineering were able to define the overhaul scope for the modern alternative BCU/CCU and determine the overhaul periodicity - based on the coding relay duty cycle associated with each train fleet. This resulted in de-coupling the BCU/CCU overhaul from the train overhaul.


Stage 1 - Overhaul Periodicity: The BCU/CCU transfers the input from the drivers brake controller into a binary signal recognised by the braking system to apply the desired stages of brake force. The internal coding relays are frequently changing state whilst the train is in operation therefore the estimated electrical life had to be established in order to determine the overhaul periodicity (At which point the relays are renewed). The OTMR (On Train Monitoring Recorder) data of a number of units was used to establish the duty cycle of each relay and the electrical load was considered against the manufacturer's specification to determine the overhaul frequency.

Stage 2 - Component Overhaul & Test Instruction: An overhaul instruction had not been provided by the OEM therefore an overhaul & test instruction needed writing along with the associated engineering change documentation to justify the scope. The customer provided a spare BCU/CCU so that the overhaul & testing documentation could be fully developed and approved for use by the ROSCO's (the owners of the two train fleets).


In addition to the overhaul & test instruction a test box was designed and manufactured to reduce human factors issues during testing and speed up the BCU/CCU post-overhaul testing process.

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