At this stage, much more resource is employed as the BASIC PLAN gets underway. The costs will begin to escalate.
In terms of project RISK the biggest weakness will be the management and control systems.
At this stage, ideally, the base plan contains reactive mitigating activities for particular identified risks together with triggers for contingency plans.
Any modifications arising from the earlier stages, e.g. design, could have a detrimental affect in the plan execution stage.
This could result not only in time delays but will almost certainly increase costs.
Some consideration and modification of the plan is almost inevitable.
Plans rarely if ever go as we would wish.
Any modifications to the plan should be assessed for RISK implications.
However, some of the problems will be RISKS that have not been identified in the earlier stages and are now coming to fruition.
A more detailed treatment of the planning and execution phases looking at objectives, milestones and many other aspects is covered in 'The Complete Project Management [see ‘The Complete Project Management package’] and [see 'The Complete Project Management plus PRINCE2'] Package' in this series.