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Case Studies

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.

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.

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.

New Train Fleet Rescue/Recovery Procedures

Following an operational incident involving a failed train the customer requested that their train recovery procedures (used by Operations staff) be improved. The knowledge base required to deal with serious service affecting failures involving a brand new train fleet was limited amongst Operations staff therefore a robust, easy-to-use set of train recovery procedures needed to be in place to deal with future incidents effectively.


Trevally engineering worked closely with the train manufacturer and operator to scrutinise the new procedures and conducted a number of working reviews to mimic each failure scenario. The aim of this was to help Operations staff recover failed trains in a timely and safe manner.

New Train Fleet Vehicle Maintenance Instruction (VMI) Re-Write

The customer informed that their new train manufacturer had supplied a suite of Vehicle Maintenance Instructions (VMI's) that were suited to ‘DC’ depots only. The customer intended to maintain the new fleet at both ‘AC’ & ‘DC’ depot facilities. All 160 vehicle maintenance instructions were re-written to include the relevant information to enable the trains to be safely maintained at both AC & DC depots.


Particular attention was given to the train safety status of each instruction to reduce the risk of injury to maintenance personnel. During this work a number other technical and non-technical changes were made to address outcomes from locally raised non-conformances and National Incident Reports.

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C6 Overhaul - Mobilisation & Engineering Support

The customer requested that the C6 overhaul documentation be re-written from a contractual style document into a full suite of working instructions to facilitate the upcoming overhaul program. In order to create working instructions each element of the overhaul needed to be precisely understood and documented. This information meant that a bill of material could be created and also enabled the supplier to provide an accurate quotation.

Research of historic documentation, drawings and circuit diagrams was required initially; however unit inspections and in some cases working reviews were necessary to fully understand each element. As the project developed Trevally Engineering were also able to provide on-going engineering support to address technical queries raised by the supplier during the project. 

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Maintenance Plan Optimisation

The customer’s train fleet was being moved to a different maintenance facility. This maintenance facility has a number of operational restrictions; meaning logistically it can be difficult to bring trains back to the depot for maintenance.

There was a need to optimise the maintenance plan to facilitate the depot restrictions. This required a 20% mileage extension so that only one major exam per week was carried out.

Whilst carrying out the maintenance plan optimisation Trevally Engineering also updated various maintenance tasks to include a new train monitoring system, other minor modifications and improved working practices.

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