UNCERTAINTIES
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There is inherent variability in work makes it difficult to follow
schedules.
There is competition for people, facilities and other equipment within
and across products – work waits in queue
Unpredictable work cause schedule delays.
Frequent priority changes force constant shifting of resources.
Delivery dates move as customer needs change
Variability in work scope
Administrative delays (paperwork, system related, Inspection reports,
Customer approval, …)
Differences between Delta demand and customer demand
Data integrity in system
Aging equipment increases unscheduled down time
Distractions due to business level uncertainty
Etc, Etc, Etc………
DELTA AIR LINES, INC.
1
Before TOC
How Products Flowed –
Engine Maintenance = Engines, APU’s, Landing Gear
Outside Repair
Product
Disassembly
Scrap Replacement
Repair & Support Shops
Product
Assembly
&
Test
Historical 4 year monthly average production = ~38 engines/mth
20,000 open shop orders to support 60 + engines in WIP
DELTA AIR LINES, INC.
2
Policy Constraint(s)
Intrinsic
Uncertainties
Uncertainties
multiply
Delays

Lines
Start Early
(CT )
High no. of
jobs in progress
Delays/
Shortages 
Lead time 
Backshops
Resource
contention 
(Queues )
3
DELTA
AIR LINES,
INC.Inc
Realization
Technologies,
“If I just had my !@#$ parts…”
Originally focused on Disassemble and release of Parts
ASAP
• Created excess WIP
• Little’s Law*
• Competing priorities
• Customer vs. Delta
• Day Cards, Green Cards, Manager Specials
• Long Queue Times vs. Short Touch Times
• Long TAT and Low Through-Put
• Parts late to Outside repair vendors
DELTA AIR LINES, INC.
4
Implement Theory of Constraints
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Metrics –Throughput, Turn Time, WIP
Drum Buffer Rope Scheduling (Repair Shops)
Exception Management
CCPM (Product Lines)
DELTA AIR LINES, INC.
5
Simplified Drum-Buffer-Rope
Drum Determined by Due Date
Established a 15 day rope
• 10 working days plus 5 days of Buffer
• Determined by Longest Lead-Time part
• Approx. 156 process hours, ~ 6.5 days
• Most parts require < 3 days Touch-Time
• Typical parts repair averaged 60 days
• Now 10 days, 7 days plus 3 days of buffer
Control release of Material
• Work to the rate of R&S (Constraint)
• Established Parts Release mechanism to protect the system
• Parts sent to Holding Area to wait for release
• Release Exception Parts ASAP
• Release Non-Exception Parts at A15, now A10
• Repair Gate Manager—sets schedule & priority
DELTA AIR LINES, INC.
6
Exception Management
Production Meeting each Day
• D+2 & D+7 Validation
• BOMs complete
• Exception Parts released
• Non exception parts in holding area
• A-2 Communication
• Identify parts that will miss start date
• Determine options
• Wait, protected by Project Buffer
• Expedite—20 Tags monitored
• Swap—available part
• Work with Supplier/Vendor for Solution
• Buy
DELTA AIR LINES, INC.
7
CCPM
Introduced Critical Chain rules to manage Product Lines
• Treat each Product as a project
• Pipeline (staggered) Products across all lines to protect
the system
• Transitioned from precise, Task-Level management to
Simple Milestones (Concerto)
• Explicit time buffers
DELTA AIR LINES, INC.
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DELTA AIR LINES, INC.
9
Current Execution Process
INDUCTION
(I ZERO)
DISASSY END
(D ZERO)
D+2 D+7 A-10
ASSY BEGIN
(A ZERO)
A-3
TEST
(T ZERO)
A-2
Stagger
Inductions
DISASSEMBLY
• All exception parts
routed
• Complete BOM BY
D0
• Ensure all
exception parts out
by D+2 & D+7
follow up
HOLD FOR
RELEASE
• Minimizes R&S WIP
levels
• Ensures only parts
that are needed are
in work
• Results include
increased
throughput and
decreased TAT
PARTS
REPAIR
• All shops
follow RED,
FIFO priority
in RGM.
Expedite tags
used only for
emergency
ASSEMBLY
• Do not begin
until 100% of
parts are
received
• Use OT only
to regain lost
buffer
DELTA AIR LINES, INC.
10
Summary of Changes
Create Plans with Buffers
• Developed aggressive project plans with buffers for Product lines
• Setup FIFO/red/expedite priority system for all piece parts
Control WIP
• Control the release of Products into the system based on WIP
• Hold non-exception parts until A-10
• Do not start assembly until all parts are available
Manage Using the Buffers
• Turn parts red 3 days before the start of assembly
• Assign work based on buffer priorities
• Allocate resources to red parts and/or red tasks
Exception Management
• Review D+2 and OSR parts at D+7 to ensure on-time delivery
• Review all parts starting A-2 and make decisions if A0 will not be
met
DELTA AIR LINES, INC.
11
Results
WIP:
• Was 20,000 Piece Part WIP 
6000 Piece Part WIP
TP:
• 25% increase in piece part repair
• 97+% parts back at A0
• 23% increase in engine production within first year
• 50+ engines per month produced consistently
Turn Time:
• 70% Reduction in Piece Part TAT
• Engine total TAT reduction – 40% AVG across all product lines
• Landing Gear TAT reduction – 60%
• Robert Fox Award—Operational Innovation
DELTA AIR LINES, INC.
12
Next Steps
TOC implementation has continued to drive the flywheel faster YOY
Next steps:
1. Distribution Solution
2. Focus on Outside Repair Vendors and New Material Supply
Processes
3. Attention around exception management
4. Improve synchronization
DELTA AIR LINES, INC.
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Questions?
DELTA AIR LINES, INC.
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