Principal Engineer - Train Tech (m/f/d)

At Flix, our mission is to revolutionize mobility: making travel greener, smarter, and more accessible. While FlixBus transformed long-distance coach travel, FlixTrain aims to transforming rail industry. Operating trains differs significantly from operating buses: it requires specialized processes and tools. To support this mission, Train Tech currently comprises three cross-functional teams: Locomotion , Steam , and Momentum focused on building, iterating, and scaling our OMS. In the future, the number of teams will grow to allow for future optimisation and expansion. As Principal Engineer (m/f/d) , you will play a critical leadership role in shaping and delivering a best-in-class OMS that powers FlixTrain’s future growth. You’ll be at the heart of building technology for what will become a multi-billion-euro business: driving foundational decisions on architecture, infrastructure, and product direction. This is a rare opportunity to \“play with trains” (metaphorically speaking): you’ll work on systems that directly impact timetables, crew assignments, and real-time operational resilience. Joining Train Tech feels like a startup within a global enterprise: you’ll benefit from Flix’s scale and resources while enjoying the autonomy, speed, and creative freedom of a tight-knit, mission-driven team. You’ll collaborate daily with passionate engineers, product owners, UX designers, and operations experts who genuinely care about transforming rail mobility. If you want to make a tangible impact, where your technical vision becomes the backbone of a rapidly growing product, this role is for you. You’ll shape not only the software but the future of rail travel in Europe. Our Tech Stack : Backend: Java (Spring Boot), Frontend: React, Honeycomb Infrastructure as Code: Terraform Databases: PostgreSQL, MongoDB Mobile: Kotlin Multiplatform Messaging/Event Bus: Kafka Key Challenges: Effectiveness vs. Complexity: Leveraging bus-oriented services can save development time, but adapting them to train-specific requirements introduces architectural complexity. You’ll help teams balance reuse with building train-native solutions. Pressing Deadlines & Technical Debt: Many critical train-specific workflows should have been addressed a year ago. The resulting backlog puts pressure on teams to deliver quickly without sacrificing long-term maintainability. Quality vs. Speed: With a small initial user base, we rely heavily on early adopters’ feedback. You’ll guide us in defining quality gates at each iteration—ensuring stability while maintaining rapid releases. Cross-Domain Ownership Gaps: Critical train systems (e.g., the Traffic Control telephony system) currently fall outside any single team’s scope. You’ll drive alignment across teams, defining clear ownership and integration points. About the role Lead & Architect Train-Specific Initiative – Oversee the end-to-end architecture of train-native modules – Evaluate and drive alignment: when to extend existing bus-services versus building new train-optimized components. – Shape the infrastructure and network architecture for future FlixTrain fleets (including hardware tender contributions, networking requirements, and on-board connectivity). Drive Cross-Team Collaboration & Ownership – Act as the technical layer between Locomotion, Steam, Momentum, and upcoming teams. Ensure shared standards (APIs, event schemas, security practices) and reduce duplicated effort. – Champion domain topics that lack clear ownership, such as the Traffic Control telephony system, ensuring critical subsystems are built, maintained, and documented. Elevate Engineering & Delivery Standards – Establish best practices for iterative development, testing (unit, integration, end-to-end), and deployment pipelines, balancing agility with reliability. – Mentor senior engineers, fostering a culture of code reviews, pair programming, and shared ownership. – Guide teams in identifying technical debt and planning refactors without jeopardizing tight deadlines. Represent Train Tech in Leadership & Strategy – Participate in Division-level leadership meetings, ensuring train-specific priorities and constraints are heard and acted upon. – Advocate for investment in train-specific capabilities (e.g., central ride inventory management within Supply Side). About you Have 7-10 years of software engineering experience, with at least 3 years in a principal/staff role Understand the complexities of transportation/operations systems, ideally within rail, aviation, or other regulated industries. Experience with rail ops is a strong plus. Are fluent in Java/Spring Boot (Kotlin knowledge is desirable) and has hands-on experience with React and/or mobile technologies. Have led multi-team architectures, defining APIs, microservice boundaries, database schemas (Postgres, MongoDB), and event streams (Kafka). Are comfortable with Infrastructure as Code, CI/CD pipelines, and cloud-native design patterns (Terraform experience preferred). Have a track record of balancing delivery speed with long-term maintainability, demonstrating sound judgment on technical debt vs. feature velocity. Excel at stakeholder management and communication you can translate complex technical trade-offs into business-friendly terms and influence leadership. Are a hands-on mentor and coach, passionate about growing engineers and building high-performing teams. Thrive under pressure you remain calm when deadlines loom, making data-informed decisions and rallying teams to deliver results. We recognize that everyone carries a unique set of valuable skills and experiences. If you think you could have an impact even though you don\’t meet 100% of the requirements, we still encourage you to apply. We want to hear from you! What We Offer Travel perks : 12 free Flix vouchers + 12 discount vouchers for friends & family. Work from (M)Anywhere : Depending on your role, work from another location for up to 60 days per year. Hybrid work model : We are an office-first company, but we offer flexibility to balance work and life. Wellbeing support : Access confidential 1:1 counselling, courses, and stress management for yourself and up to four family members. Learning & Development : Take advantage of language classes, training courses, and expert-led sessions to grow your skills. Mentoring Program : Connect with experienced colleagues to gain insights and accelerate your career. Why Join Flix? At Flix, we empower our teams to push boundaries and shape the future of mobility. As we continue to scale globally, we harness cutting-edge technology to make mobility smarter, more sustainable, and more affordable. If you’re looking for a place where you can drive change and redefine how millions of people travel, Flix is the place where you can lead your journey!