During the design and implementation of engineering systems, as project members solve problems and exchange information with each other, a complex network of organisational interactions is established. The study of organisational networks can provide us with a deeper understanding of how organisations function and can help us devise strategies to improve collaboration and communication. However, it is widely believed that communication networks accurately capture the underlying collaboration amongst the members of an organisation. Here, through the use of multilayer and temporal network analysis methods, we analyse collaboration (through the project activity log) and communication (via emails) in a large engineering project and find that, on the contrary, collaboration and communication networks are only weakly correlated. More importantly, collaboration and communication networks show diametrically opposite purposes, underscored by crucial topological differences. While the email communication network is organised to facilitate the spread of information, the collaboration network is organised to suppress error propagation. We discuss the implications of our findings on how to design organisational networks and how to foster effective communication.