Mainframe Assembler Engineer (CICS/MQ/z/OS)

Mainframe Assembler Engineer (CICS/MQ/z/OS)

Duration: 6 months
Location: Edinburgh, Manchester OR Leeds
Working Hours: Monday to Friday, standard business hours, plus participation in a 24/7 on-call rota
Start date: 05/01/2026
Onsite Requirements: 2 days per week onsite
Day Rate: £500 - Outside IR35

Gibbs Consulting is supporting a major financial services client with the appointment of an experienced Mainframe Assembler Engineer to join their Heritage Mainframe Engineering team.

Job Overview
This role is responsible for delivering both BAU operational support and technical change within a mission-critical IBM z/OS environment. You will work across Assembler, CICS, and MQ components to ensure the stability, performance, and modernisation of core banking services. The position involves troubleshooting incidents, performance tuning, supporting project delivery activities, and participating in out-of-hours deployments to ensure continuous service availability.

RESPONSIBILITIES
* Provide expert support for Assembler components and integration with CICS and IBM MQ subsystems
* Perform root-cause analysis for incidents, abends, and performance issues across production and test environments
* Participate in a 24×7 on-call rota supporting business-critical systems
* Maintain and optimise JCL batch processes, MQ message handling, and CICS transaction performance
* Ensure compliance with ITIL governance, risk controls, and ServiceNow processes
* Support upgrades, migrations, and change delivery across the Mainframe estate
* Develop and modify Assembler code for planned releases and transformation initiatives
* Collaborate with Cobol, DB2, and infrastructure teams to deliver integrated solutions
* Contribute to test support, release validation, and deployment readiness
* Provide technical input into design reviews and documentation

REQUIREMENTS
* Proven expertise in IBM High Level Assembler (HLASM) development and support on z/OS
* Strong knowledge of CICS, IBM MQ (v9.x+), JCL, and VSAM in high-availability environments
* Incident resolution experience using Abend-Aid, File-Aid, Omegamon, IPCS or similar tooling
* Hands-on MQ administration and performance tuning on z/OS
* Experience supporting operational BAU and project delivery activities
* Familiarity with Cobol, DB2, and cross-component troubleshooting
* Security and compliance understanding including TLS and MQ channel security
* Automation and Scripting skills (eg JCL utilities, REXX, Shell, Ansible, UrbanCode)
* Excellent communication and collaboration skills with cross-functional teams
* Flexibility to support out-of-hours activities when required