Subject Matter Expert (Mainframe Systems Engineer/Programmer working on System Z mainframe envi[...]

NATS is the UK’s leading air navigation service provider, handling over 2.4 million flights each year. We provide air traffic control services from two control centres and at airports around the UK. We also provide a wide range of commercial products and solutions internationally. Our people are at the heart of our purpose to advance aviation and keep the skies safe.

Closing Date: 2/2/2026

Please Include a Cover Letter with your application. Please Note: This role will ideally require regular office attendance.

Job Purpose/Overview

We are looking for a systems engineer to join and complement our existing team in supporting our IBM mainframe environment. The ideal candidate will have a solid IBM system programming background, hands‑on experience configuring IBM Z servers, and a good working knowledge of REXX. This is a role within the Flight Domain of the Systems Engineering and Software Engineering team, working on both asset sustainment and transformation programme delivery.

System areas include: Flight Data Processing, Queue and Capacity Management, Separation Provision, and Traffic Synchronisation Tooling. The specific system in this case is the NAS Bureau, which will involve tasks such as:

• Working in an IBM System 390 or System Z mainframe environment, in a system programmer capacity, where familiarity with IBM operating systems such as VM/ESA, z/VM, OS/390, or z/OS will be beneficial.
• Coding using the IBM Rexx programming language or other programming languages such as Visual Basic, C, or Python.
• Analysing, diagnosing and resolving system faults, where it will be advantageous to have a working knowledge of IBM System 390 or System Z mainframe hardware architecture.
• Producing technical documentation, including local procedures and operational work instructions, where knowledge of the NAS development lifecycle would be advantageous.
• Collaborating within a small, focused team to drive successful solutions.

Other Duties

• System Expertise & Support: Serve as one of the primary technical experts for assigned system(s), supporting operational assurance and system understanding across the Domain.
• In-Service Asset Assurance: Maintain and update key system documentation including but not limited to Work Instructions, Security Risk Assessments (SRAs), System Architecture Documents (SADs), and Technical Files. This also includes maintenance of Operational Support environments as needed.
• Regulatory & Safety Documentation: Support the upkeep of regulatory documentation and safety assurance artefacts to ensure continued compliance.
• Problem & Change Support: Contribute to the analysis and resolution of PTRs (Problem Tracking Reports) liaising with operational units and support the definition and implementation of changes to in-service systems.
• Transformation & Change Projects: Provide system-specific input to transformation initiatives and asset change projects, as requested by the Domain Leadership.
• Collaboration & Communication: Work closely with the Domain Leadership, Project Managers, Engineering Leads, and other SMEs to ensure consistent and informed decision-making.
• Continuous Improvement: Stay informed of industry trends, technology developments, and operational feedback to identify opportunities for system improvement.

Autonomy

Operates with autonomy in system-specific matters under the direction of the Domain Leadership. Responsible for delivering agreed outputs and maintaining system documentation and assurance artefacts. Escalates decisions outside of agreed scope, all within the boundaries of NATS Business Management processes (BMS).

Job Scope

• System Support: Acts as the internal expert for one or more systems, ensuring continuity of knowledge and technical integrity.
• Documentation & Assurance: Maintains system documentation and supports assurance processes, including updates to safety and regulatory artefacts on behalf of Domain Leadership.
• Support to Projects: Provides input to change and transformation projects, ensuring system-specific considerations are addressed.
• Stakeholder Engagement: Interfaces with internal stakeholders and, where appropriate, external suppliers or regulators on system-specific issues.
• Technical Expertise: Provide technical input throughout project phases, providing efficient resolution of issues to stakeholders.
• Design Envelope Evolution: Assist in defining and refining the design envelopes for in-service systems, ensuring alignment with operational needs and future capability.

Essential Skills and Experience

• Qualifications: The post holder is expected to hold, as a minimum, a Higher National Certificate in an Engineering or Information Technology related discipline, and relevant experience. Job holders not holding the expected qualification but who have undertaken structured technical training (e.g. apprenticeship recognised by a professional body) with recognised qualification ideally to at least HNC equivalent level will also be considered.
• Experience: Experience in systems engineering or technical support roles, ideally within safety-critical or real-time environments. Familiarity with the assigned system(s) is highly desirable.
• Knowledge: Strong understanding of the assigned system(s) and their operational context. Familiarity with relevant technical standards and assurance processes.
• Skills: Strong problem-solving ability, understanding of the systems engineering lifecycle, effective communication skills, and attention to detail with a commitment to quality. Expected to align with skills from SFIA Systems Design Level 3.

Additional Vacancy Information

We are proud to offer a fantastic total reward package to help you thrive both personally and professionally. We have adopted agile working to provide greater flexibility and increased choice over working arrangements, with the opportunity for this role to work in our modern office facilities as well as remotely. We also welcome discussions on flexible and part-time working arrangements.

If you share our passion to advance aviation and keep the skies safe – we would like to hear from you whatever your age, sex, race, faith, sexual orientation, gender identity, gender expression, visible or invisible disability. Individuals that bring different perspectives, skills, life experiences and backgrounds help us be at the forefront of our industry.