Most sorter installations do not fail loudly. They slip a few days at a time, in gaps between trades, in late deliveries nobody escalated, in site work that started late because an earlier decision was never closed. By the time the delay becomes visible in the go-live date, the recovery options are expensive ones: overtime, weekend shifts, or compressed testing that pushes defects into production. A well-built project plan exists to make those small slips visible while they are still cheap to fix.
The plan is not a document produced to satisfy a contract clause. It is the operating model for the installation: who does what, in what order, and what has to be true at each point before the next activity can start. This article sets out how to structure that plan for a sortation system and which milestones carry the schedule.
Work Backwards From Go-Live
The most reliable way to build an installation schedule is to start at the end. Fix the go-live date – or the date the line must support a defined pilot volume – and schedule backwards: commissioning, integration testing, mechanical completion, power-on, installation start, site readiness. Each step inherits its latest permissible start from the next, and the gap between that start and the realistic one is your float. When the float on a step is thin, that step is a schedule risk worth attention, whatever the reason for it.
Working backwards also exposes sequencing problems early. Commissioning needs power, network and a proven safety perimeter before it can start; installation needs finished floors, access and storage space; site preparation needs a frozen layout. If any of these dependencies cannot be met on the proposed dates, the go-live date is a wish rather than a plan, and it is better to learn that in the planning room than in week six.
Define Milestones as Verifiable States
A milestone that says “installation complete” is not a milestone; it is an opinion. Define each one as a state that can be verified in a walk-through or a test:
- Design freeze: layout, chute positions and interface drawings signed by both parties. Nothing downstream starts reliably before this.
- Site ready: floor tolerances measured, power available at the agreed point, network drops live, access confirmed – the conditions covered in a readiness review.
- Mechanical completion: loop assembled and aligned, chutes fixed, guarding fitted, with a signed inspection record.
- Power-on: drives energised, controls tested, safety circuits proven, and the line able to run empty.
- Integration proven: host system exchanging data with the sorter control, verified end to end with test parcels.
- Performance acceptance: the line demonstrates contracted throughput and accuracy over the agreed test window.
Verification matters because payment tranches and downstream activities are usually tied to these dates. A milestone that cannot be objectively confirmed becomes a negotiation, and negotiations consume schedule.
Build the Critical Path Around Site Work
On paper the critical path looks like it runs through the equipment: delivery, assembly, wiring, commissioning. In practice it usually runs through site work and decisions. Floor preparation that starts a week late pushes everything after it; a chute count revised during installation reopens the layout, the electrical design and the delivery sequence all at once. The critical path on a sorter project is rarely the longest list of tasks – it is the chain of approvals, readiness conditions and interface completions that gates the machine work.
Identify that chain explicitly and manage it separately from the task list. Ask at weekly level: what is currently gating the next activity, who owns the gate, and what date will it clear? A plan that tracks task progress without tracking gate owners will report eighty percent complete for weeks.
Manage Float Without Hiding Risk
Float is not slack to be consumed silently. Two habits keep it honest:
- Report consumption: when an activity uses float, say so. Float consumed on the critical path is schedule lost, even when the date has not yet moved.
- Recover early: recovering a week of slippage in week two costs an adjustment; recovering it in week eight costs overtime and a compressed test plan.
Also distinguish float inside the installation from float the site controls. A supplier holding two days of commissioning float cannot compensate for a building that is not ready, and the plan should make that boundary explicit rather than leaving both parties to assume the other owns the risk.
Technical Background
The visual spine of the plan is usually a Gantt chart, which shows activities against time and makes dependencies visible. Sequencing logic and float analysis come from the critical path method, which identifies the chain of activities that determines the project end date. A milestone in project management terms is a point in time with zero duration – which is exactly why it must be defined by a verifiable state rather than by a task being mostly done.
For buyers, the plan also belongs in the contract rather than only in the project room. Milestones tied to readiness conditions and payment tranches are covered in payment milestones and performance security, and the site-side conditions are itemised in the site readiness checklist. The phases themselves follow the structure in installation and commissioning, and the test criteria at the end of the schedule are set out in FAT and SAT acceptance testing.
Reporting Cadence and Change Control
A schedule is only as good as its reporting rhythm. A weekly cadence is usually right for a sorter installation: short, standing, and structured around the same three questions – what moved, what is gating, and what needs a decision now. Daily reporting is justified only in the final two weeks, when small delays have nowhere left to hide.
Change control is the other half. Layout changes, chute additions and scope adjustments will happen; the discipline is that each one gets a schedule and cost impact in writing before it is approved, and the plan is re-baselined rather than quietly patched. A plan that absorbs changes without re-baselining stops being a reference and becomes a story about what should have happened.
Finally, define what happens when a milestone is missed, before it is missed. The mature version is boring: a revised date, a recovery option and a named owner. The immature version is a debate about cause that starts after the date has passed and consumes the very time recovery needs. Projects that write this rule into the plan in advance spend their energy fixing schedules instead of arguing about them – and the defects that survive a compressed schedule get managed through the process in the commissioning punchlist and defect closure process rather than into live operation.
Frequently Asked Questions
How long does a sorter installation take?
On-site work for a mid-size line is typically several weeks, but the overall schedule is dominated by lead time, site preparation and design decisions made months earlier.
Which milestone slips most often?
Site readiness and design freeze. Both gate downstream work, and both depend on decisions and conditions outside the supplier’s direct control.
How much float should the plan hold?
Enough to absorb one recovery cycle at the thinnest point of the critical path – usually days, not weeks – and it should be visible, not buried inside task durations.
Who owns the schedule?
The supplier normally runs day-to-day execution, but gates that depend on site conditions are buyer-owned. The plan should state that split explicitly.
When should integration testing be scheduled?
Before performance acceptance and with its own window. Booking it into whatever time remains at the end is a common cause of compressed, unreliable testing.
Should payment follow milestones?
Commonly yes, with each tranche tied to a verifiable state such as mechanical completion or performance acceptance rather than a percentage-completion claim.
What reporting cadence works best?
Weekly through installation, moving to daily in the final two weeks, always structured around slippage, gating items and decisions needed now.