🎓 CSSBB Quest › Section VIII

Section VIII — Control Phase ~11%

Control carries about 17 of the 150 scored questions, and it matters more than its weight suggests: a project with a weak Control phase reverts. The 2022 BoK covers statistical process control (SPC), other controls (total productive maintenance and the visual factory), maintaining controls (measurement system re-analysis and the control plan), and sustaining improvements (lessons learned, documentation, training, ongoing evaluation). Questions focus on which control chart to use, how to interpret its signals, what a control plan contains, and how to hand off to the process owner.

Control phase deliverables

Deliverable	What it contains	Who owns it after the BB closes the project?
Control plan	For each key process input variable (KPIV) and key output variable (KPOV): what to measure, how, frequency, sample size, control method, and reaction plan	Process owner
Updated process documentation	Revised SOPs, work instructions, training materials reflecting the improved process	Quality/documentation system
Statistical process control (SPC) charts	Ongoing monitoring of in-control limits established from the improved process	Process operator/process owner
Other controls	Total productive maintenance (TPM) to keep equipment capable; visual controls (visual factory) so abnormal conditions are obvious at a glance	Process owner
Measurement system re-analysis	Periodic MSA so the gauges used for control stay adequate as the process improves	Quality / metrology
Lessons learned	What worked, what to do differently, tools and insights for future BBs	MBB / program manager
Project closure report	Final capability results vs. baseline, validated savings, benefits realization timeline	Champion and Finance

Selecting the right control chart

Data type	Subgroup size	Chart
Continuous (variables)	Individual measurements (n = 1)	I-MR (individuals & moving range)
	Small subgroups (about 2–9)	X̄-R (X-bar and range)
	Larger subgroups (about 10 or more)	X̄-s (X-bar and standard deviation)
Attribute (discrete)	Defective units, constant subgroup size	np-chart (count defective) or p-chart (proportion defective)
	Defective units, varying subgroup size	p-chart (control limits vary with n)
	Tracking count of defects (not defectives) per unit	c-chart (constant sample) or u-chart (variable sample)

Exam trap: defective vs. defect — a defective unit is a unit that fails (pass/fail); a defect is a single nonconformance on a unit. A unit can have multiple defects. p- and np-charts track defective units; c- and u-charts track defects.

Common out-of-control tests

The classic Western Electric rules (zones measured from the center line):

Rule 1: One point beyond the 3σ control limits
Rule 2: Two of three consecutive points beyond 2σ on the same side
Rule 3: Four of five consecutive points beyond 1σ on the same side
Rule 4: Eight consecutive points on the same side of the center line

Software often uses the related Nelson tests instead, such as nine points in a row on one side (a shift), six points in a row steadily increasing or decreasing (a trend), and fifteen points in a row within 1σ of the center line (stratification).

Exam trap: fifteen points hugging the center line looks like “great stability” but usually means the control limits are too wide — for example, subgroups mix several streams or the limits were calculated from the wrong data.

Reaction plan — what must it contain?

The reaction plan in the control plan answers three questions for every out-of-control signal: (1) Who is responsible for the response? (2) What immediate action stops the process or prevents product release? (3) What investigation or escalation path follows?

A reaction plan that says “notify supervisor” is insufficient if it doesn’t also say what the supervisor does and how the root cause is investigated before restarting.

Handing off to the process owner

The BB’s job ends when the process owner can maintain the gains independently. The handoff package includes the control plan, the SPC charts with established limits, training records for operators, and updated documentation. The BB should plan a follow-up review after handoff (the length is set by the organization and the process) to verify gains are sustained before formally closing the project.