The researchers conducted an indepth field project to study the planning and scheduling process in the printed circuit board industry. The formal versus informal scheduling practices are compared, and several aspects of the scheduling situation discussed. Heuristics and techniques used to address instability in the manufacturing system are presented. Instability refers to the manufacturing state when expected or unexpected changes are encountered—e.g. changes in policies, procedures, or a machine fails. The ability to encode the heuristics as a formal model or computer program and have the heuristics mechanically applied is also discussed. The study also provides insights regarding the existence and nature of scheduler expertise.