There are three roles involved here: planners who plan the jobs, supervisors who supervise their crews and schedulers who create the work schedule.
Planning, as stated before, is all about what work gets done and how.
Scheduling is about when the work gets done. The practical constraint is that no work goes on a schedule until you are sure you have everything you need to execute that work when you schedule it.
It’s like baking in your kitchen. You wouldn’t start a cake or other baked good, without the ingredients being on hand unless you knew they were coming in on time before you need to use them. So, if the baking soda isn’t available you’ll make sure you get it before you start. If you don’t, then your baking will be stalled while you go get it. Maintenance is much the same. Don’t start until you have all that you need on hand.
Making sure all that is available isn’t planning. Planning actually tells you to want you will need – it’s sort of like writing the recipe. Planning is done by a planner. Scheduling is an activity in which we check on availability of resources before putting the job onto the works schedule for any given week. Scheduling is done by a scheduler or, in many organizations, by a planner. Regardless of who does it, planning and scheduling are two different activities.
Arguably the checking on resource availability (particularly for parts and materials) is neither planning nor scheduling. It is a resource marshalling or coordination role. Since most of the work is about making sure parts are available. Indeed, some organizations have a materials coordinator role that supports scheduling using the materials called for in the job plans that are created by planners. That materials coordinate can work for the materials/supply chain people or for maintenance – it really doesn’t matter, but the function is critical to scheduling.
OK – so planners can schedule work, but it doesn’t need to be them. Scheduling does not take the technical skills/knowledge that planning requires. It really only requires good organizational skills to produce a schedule. The nature of the work being done by the trades being assigned to the work is not really relevant to scheduling. However, the number of trades available with those skills as specified in the plan is needed.
Should a supervisor schedule? My answer is no, although it is a somewhat common practice.
Wherever I’ve seen supervisors doing the bulk of the work scheduling, they are doing it in response to the immediate priorities of the operational departments, which are usually driven more by emotion than accepted scheduling parameters of priority and criticality. They must, by the nature of their work, maintain good relationships with operational staff. It is quite natural for them to want to please their “customer” in operations. In doing so, they often bow to the wishes of the day, meaning (usually) whatever the operator says he needs. Operators are not usually worried about overall production goals, they are interested in what is happening on their shift. Anyone who has operated in a plant or factory or similar environments will attest to that. If something is going to go wrong, you don’t want it to happen “on my watch”.
Supervisors are too close to the day-to-day ups and downs of normal operations and dealing with the myriad of problems that invariably arise, to do a good job of scheduling. They tend to be very good at reacting and putting out the panic-du-jour, but not always so good at looking far ahead. Scheduling looks farther ahead and considers more factors than a supervisor will have top of mind. Scheduling should be done by the scheduler or planner who does scheduling taking into account priorities, criticalities, the availability of resources across the trade and plant, availability of materials for each job, willingness of operations to release equipment for work, etc. Doing that on the fly as supervisors will tend to do (most of the time) risks ignoring some critical factors and sub-optimizing the workforce deployment and overall effort to keep backlogs under control.