In large engineering projects, conflicts arise when project activities compete for limited and shared resources. For example, a construction company executes two or more projects with thousands of tasks, located on different sites, competing for the same equipment, tools, materials, and workers. This belongs to the Resource Constrained Multi-Project Scheduling Problem (RCMPSP) involving constraints defined on multiple projects. It is a problem that none of the existing single-project RCPSP approaches can deal with easily. The key to coordinating multiple projects is to detect and resolve the conflicts through a decision making process. This paper proposes an interactive decision support method to achieve the balancing of multiple objectives - time, resources, and performance for the coordination of multiple concurrent projects. Interactive decision support means detecting conflicts, prioritizing projects, proposing potential options, as well as calculating the ripple effects of each step after a decision is made. The proposed approach and related algorithms have been fully implemented and tested in a web-based aircraft periodical inspection and maintenance system and are being applied in other ongoing projects for multi-project coordination in construction and facilities management.