The present article describes and evaluates collaborative interdisciplinary group projects initiated by content lecturers and an English-as-a-Foreign-Language (EFL) instructor for the purpose of teaching technical writing skills in an aeronautical engineering degree program. The proposed technical writing model is assessed against the results of a learner survey and refined accordingly. The survey showed that learners appreciated the cross-disciplinary collaboration in projects, and it delivered important insights into learning effects and student progress in both language and content matters. The article concludes with a list of recommendations for the implementation of project-based collaborative technical writing instruction, which may support or complement academic writing courses in similar contexts. The proposed model considers the circumstances of students in workload-intensive tertiary settings and synthesizes approaches such as problem-based learning, content-based instruction, task-based language teaching, a guided product approach to collaborative writing, and learner autonomy.