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Airline Fleet Readiness:
Trade-off Analysis of Alternate Maintenance Systems
1
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
2
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
3
Unstable Demand, Fluctuating Prices
20
$500.00
18
$450.00
Average
Ticket Fare
$400.00
14
$350.00
12
$300.00
10
$250.00
8
$200.00
Air Carrier Traffic
Operations
6
$150.00
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
$0.00
2000
0
1999
$50.00
1998
2
1997
$100.00
1996
4
1995
Air Carrier Operations (Millions)
16
National Average Ticket Fare (USD)
Comparison of Air Traffic and Ticket Fare
Year
Source: FAA – ATADS and BTS
4
Airline Profitability
Airline Profitability vs Time
50
Annual Profit
40
Cumulative Profit
Billions (USD)
30
20
10
0
-10
Source: BTS RITA Schedule 12 and NBER
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
-20
Year
: Recession (7/90-3/91, 3/01-11/01, 12/07-6/09)
5
Total Operating Expenses
Direct Maintenance (≈10% of Total)
Source: BTS
6
Increasing Maintenance Costs
Quarterly Direct Maintenance Cost (Adjusted for Inflation)
Billions (USD)
3.5
3
2.5
2010
2009
2008
2007
2006
2005
2004
2003
2
5
4
2010
2009
2008
2007
2006
2005
2004
3
2003
Air Hours
(Millions)
Total Quarterly Air Hours
700
680
660
640
620
600
580
Source: BTS RITA Schedule P-12
Year
2010
2009
2008
2007
2006
2005
2004
560
2003
Cost per Flight Hour (USD)
Direct Maintenance Cost per Flight Hour (Adjusted for Inflation)
7
Indirect Cost of Maintenance
Fleet Readiness: The percentage of time
that a given aircraft is in service
In Service:
Producing Revenue
Out for Maintenance:
Losing Revenue and
Incurring Costs
8
Higher
Maintenance Cost Gap
Total Cost
Maintenance Costs (direct and indirect)
Cost
Other Operating Expenses
Goal:
Lower
Current
Reduce
Cost Gap
Optimal
Lower
Frequency of part replacement
Higher
*Note: This figure is not drawn to scale.
9
Aircraft Complexity
“*A Boeing 737 has+ 367,000
parts; an equal number of bolts,
rivets and other fasteners; and
36 miles (58 kilometers) of
electrical wire” - Boeing
Source: FlightGlobal and Boeing
10
Aircraft Complexity
Boeing 737 Family
# of subsystems
System
Navigation
182
Air Conditioning
145
Fire Protection
95
Fuel
93
Communications
75
Doors
73
Lights
Equipment/Furnishings
Flight Controls
Ice and Rain Protection
63
57
52
50
All Others
309
Total: 1194
Source: Boeing and FAA – Boeing 737 MMEL
11
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
12
Problem and Need Statements
Problem: Maintenance costs are increasing
over time.
Need: Airline companies need to reverse the
current trend of increasing maintenance costs.
Year
Indirect Maintenance Cost
2010
2009
2008
2007
2006
2005
2004
2003
Cost (USD)
Direct Maintenance Cost
700
680
660
640
620
600
580
560
13
Approach
Design and perform a tradeoff analysis of
alternate maintenance systems to determine
an effective method to reduce the number of
parts replaced and increase fleet readiness
14
Mission Requirements
1. The system shall conform to all regulations
imposed by governing bodies of the airline
and safety industries.
2. The system shall reduce number of
maintenance actions required by the aircraft.
3. The system shall reduce maintenance-related
expenses.
15
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
16
Scope
Phased Mx
Schedules
Part
Replacement
Ticket
Prices
Fluctuating
Demand
Non- Mx
Operating Costs
Mx = Maintenance
Boeing 737
Family
Part
Condition
Tracking
Mx Actions
Performed
Aircraft, Workshop
and Enterprise
Levels
Time Spent on
Each Mx Action
Outsourced
Mx
Other Aircraft
Makes and
Models
17
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
18
System Operational Scenario
Mx = Maintenance
19
Stakeholder Analysis
Aircraft
Primary Stakeholders
Secondary Stakeholders
Affected by equipage changes
and operational changes of
personnel on each aircraft
Workshop
Affected by changes in
infrastructure, operations, and
equipment that occur in the
maintenance facility
Enterprise
Affected by changes in airline
fleet management equipment
and operations.
Aircraft Flight Crew
X
Aircraft Passengers
X
X
Aircraft Manufacturer
X
X
Airline Fleet Operator
X
X
X
Airline Fleet Owner
X
X
X
Competing Airlines
X
X
X
X
X
X
X
X
Federal Aviation Administration
(FAA)
Federal Communications
Commission (FCC)
Maintenance, Repair, and
Overhaul (MRO) Personnel
Occupational Safety and Health
Administration (OSHA)
Tool and Part Manufacturers
Tool and Part Shipment Company
X
X
X
X
X
X
20
Stakeholder Interaction Diagram
Mx System
Regulation and Oversight
FCC
Supply Chain
OSHA
Workshop
Regulations
Aircraft
Supply
Enterprise
Revenue
FAA
Revenue
Tool and Part
Shipping
Company
Aircraft
Passengers
Enterprise
Competing
Airlines
Tool and Part
Manufacturer
Aircraft
Manufacturer
Airline Fleet
Owner
Airline Fleet
Operator
Workshop
MRO
Aircraft
Maintenance
System
Aircraft Flight
Crew
21
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
22
Design Alternatives
1. Hangar Transfer
Maintenance Bay
– Information is transferred in the
maintenance facility
– Preventative based
2. Flight Line Transfer
– Information is transferred in
between each flight
– Condition based
B49
3. Airborne Transfer
– Information is transferred during
flight
– Condition based
23
Preventative Based Alternative (1)
• Preventative Based Maintenance
– Parts are replaced on a regular schedule, based on
expected life of each part
– Parts may still be replaced if a scheduled
inspection identifies a need
– Limited maintenance data is available through
existing onboard sensors
• Hangar Transfer (1)
– Utilizes only existing maintenance sensors
24
Condition Based Alternatives (2 and 3)
• Condition Based Maintenance
– Parts are replaced with consideration for the
overall condition of the part and the aircraft
– Additional sensors required
• Adds weight, complexity, and power needs
• Flight Line Transfer (2)
– May require additional terminal infrastructure
• Airborne Transfer (3)
– May require additional communications avionics
and infrastructure
25
Alternative 1: Hangar Transfer
Mx = Maintenance
26
Alternative 2: Flight Line Transfer
Mx = Maintenance
27
Alternative 3: Airborne Transfer
Mx = Maintenance
28
Assumptions
• A1. Effects of outsourcing are negligible
• A2. Emergencies, hijackings, crashes are not
considered
• A3. Representative subsystems can generalize
to the entire aircraft
• A4. A generic “aging effect” can be ignored
• A5. The implementation time for alternatives
is negligible
29
Assumptions (cont’d.)
• A6. Only critical parts will be modeled
• A7. Only modeling part replacement
• A8. Time to replace a part will not be
considered
• A9. Overall safety will be assured regardless of
alternative
• A10. Maintenance personnel and facilities will
be available when needed
• A11. The cost of a maintenance action will not
change with respect to time
30
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
31
Model Design
Mx = Maintenance
32
Green, Yellow, Red Assignments
Green
Yellow
Red
Replacement is not required
Replacement is required but immediate action is not necessary
Replacement is required at next landing
33
Model Variables
Aircraft
• Age of Aircraft (Flight Hours)
• Maintenance Trip Needed (Y,N)
Part 1
Part 2
Part 3
Part 4
Part 5
•
•
•
•
•
Expected Life of Part (Flight Hours)
Current Age of Part (Flight Hours)
Actual Condition (R,Y,G)
Assigned Condition (R,Y,G)
Reason for R/Y/G (Predicted Life, Fault
Detection)
• Notification for Replacement (Y,N)
34
Data Input: Part Life and Selection
Older Airframes
Comparison of Reported Difficulties
1
Fuselage
Lights
Frequency of Difficulty
More Frequent
0.1
Wings
Equipment/Furnishings
Air Conditioning
0.01
Navigation
Stabilizers
Doors
Landing Gear
Flight Controls
Nacels/Pylons
0.001
Propellors/Propulsors
0.0001
Powerplant
0.00001
0
10000
20000
30000
40000
50000
60000
70000
Age of Airframe (In Flight Hours) at Time of Difficulty
Source: FAA – SDR Database (737 only)
*Note: Part selection is not yet finalized
35
Data Input: Flight Length
Number of Flights
––– Lognormal(2.05, 1.31)
Length of Flight (Hours)
Source: BTS RITA:
Form T-100 data, Average Ramp-To-Ramp Times,
2008-2010
36
Logical System Model
Mx = Maintenance
37
Design of Experiment
Input
Alternative
Maximum
Probability of Predicted Life of
Allowable
Part Failure
Parts
Yellow Parts
# hours (low)
Infinity
# hours (high)
Infinity
# hours (low)
Infinity
# hours (high)
Infinity
Infinity
# parts (low)
Infinity
# parts (high)
Infinity
# parts (low)
Infinity
# parts (high)
Infinity
# parts (low)
Infinity
# parts (high)
Infinity
# parts (low)
Infinity
# parts (high)
Output
Number of
Maintenance
Stops
Number of
Number of
Parts Replaced
Parts Replaced
With
Notification
Total Cost of
Maintenance
Low Estimate
Hangar Transfer
(Preventative)
High Estimate
Low Estimate
Flight Line
Transfer
(Condition)
High Estimate
Airborne
Transfer
(Condition)
Low Estimate
High Estimate
38
Utilities
Mx = Maintenance
*Note: Weights will be elicited by survey
39
Model Verification
• Compare total number of R/Y/G assignments
with expectations
• Compare time to part failure with available
data
• Check total number of maintenance trips for
reasonableness
40
Overview
1.
2.
3.
4.
5.
6.
7.
Context
Problem and Need Statements
Scope
Stakeholder Analysis
Design Alternatives
Method of Analysis
Project Schedule
41
Project Schedule
*Task is on Critical Path
42
*Note: $50/hour (loaded rate)
757.5 hours total
10-Apr
3-Apr
40000
27-Mar
Earned Value
20-Mar
13-Mar
6-Mar
15000
27-Feb
20000
20-Feb
13-Feb
6-Feb
30-Jan
23-Jan
16-Jan
9-Jan
2-Jan
26-Dec
19-Dec
12-Dec
5-Dec
28-Nov
21-Nov
14-Nov
7-Nov
31-Oct
24-Oct
17-Oct
10-Oct
3-Oct
26-Sep
19-Sep
12-Sep
5-Sep
Cost (USD)
Performance and Projected Cost
$37,875
35000
30000
25000
Budgeted Cost
Actual Cost
Work Performed
10000
5000
0
Week
43
CPI = Cost Performance Index
SPI = Schedule Performance Index
*Note: Index of 1.00 is performing as
expected
10-Apr
3-Apr
27-Mar
20-Mar
13-Mar
6-Mar
27-Feb
20-Feb
13-Feb
6-Feb
30-Jan
23-Jan
16-Jan
9-Jan
2-Jan
26-Dec
1.00
19-Dec
12-Dec
5-Dec
28-Nov
21-Nov
14-Nov
7-Nov
31-Oct
24-Oct
17-Oct
10-Oct
3-Oct
26-Sep
19-Sep
12-Sep
5-Sep
Index
CPI and SPI
CPI and SPI
1.60
1.40
1.20
CPI
SPI
0.80
0.60
0.40
0.20
0.00
Week
44
Risks
• Limited knowledge and experience with airline
maintenance
– Mitigation: Sponsor in the aviation maintenance
field
• Task saturation
– Mitigation: We now have an intern to assist with
non-critical tasks
45
Questions?
?
46
Backup Slides
• Failure Patterns
• Stakeholder Node Adjacency Matrix
• Service Difficulty Reports
• Model Inputs and Outputs
• Logical System Model (Expanded)
• Mx as a fraction of operating expenses
• Quarterly Direct Mx Expenses
• Airworthiness Directives
• Regulatory Pressure
48
Model
Inputs
Outputs
Number of
Maintenance Actions
Probability of Part
Failure
Number of Parts
Replaced
Predicted Life of Part
Maximum Allowed
“Yellow” Parts
Discrete Event
System Model
Average Lead Time
Before Repair
Total Cost of
Maintenance
49
Failure Patterns
50
Failure Patterns
100%
90%
80%
70%
Bathtub
60%
Exponential
50%
Linear
40%
Log
30%
Flat
20%
Decay
10%
0%
UAL
Broberg
Aviation
MSP
SUB
Naval
51
Stakeholder Node Adjacency Matrix
To
Node
Airline Fleet
Operator
Airline Fleet
Owner
Airline Fleet Airline Fleet Aircraft
Aircraft
Aircraft Maintenance Competing
FAA FCC
Operator
Owner
Flight Crew Manufacturer Passengers
System
Airlines
Aircraft Flight
Crew
Aircraft
Manufacturer
From
Aircraft
Passengers
FAA
Tool and Part
Shipping
Company
Budget
Labor cost
Need for
Fewer
Delays
Revenue
Cost
Ticket Sales
Schedules,
Procedures
Trend
feedback,
Changes in
Equipment
Regulations Regulations
MRO
Divergent
Practices
Delays
Procedures,
Airworthines
s Directives
System
Interfaces,
Additional
Training,
Procedures
Inventory Need for Fast
Requirements Shipping
Price
Competition
Ticket Prices
FCC
Regulations
Regulations Regulations
Regulations
Regulations
Certifications
Regulations
Need for
Reliable
Shipping
Labor Cost
Safety
Regulations
OSHA
Tool and Part
Manufacturer
Tool and Part
Shipping
Company
Tool and Part
Manufacturer
Cost of
Construction
Fleet
Maintenance Operations
System
Down Time,
Schedule
Competing
Airlines
Cost of
Construction,
Capabilities
Labor Cost
OSHA
Maintenance Ticket Price
Reports
Competition
Schedules
Budget
MRO
Safety
Regulations
Tools and
Parts
Shipping
Costs
Shipping
Costs
Tools and
Parts
52
Service Difficulty Reports
53
Model Inputs
• Probability of Part Failure: Expected
percentage that a part will fail based on
historical data
• Predicted Life of Parts: Mean Time Between
Failure (MTBF)
• Maximum Allowable Yellow Parts: Number of
parts nearing MTBF allowed before
maintenance trip is required
• Fault Detection Accuracy: Estimated accuracy
of the identification of a fault in the model
54
Model Outputs
• Number of Maintenance Stops: The total
number of maintenance trips performed by the
simulated aircraft during its service life
• Number of Parts Replaced: The total number of
parts replaced during the simulated aircraft’s
service life
• Total Cost of Maintenance: The monetary cost of
maintenance over the service life of the
simulated aircraft
• Average Lead Time Before Repair: Time in hours
available for preparatory work by maintenance
personnel
55
Logical System Model (Expanded)
56
System Model (Pseudo Code)
Action
Formula
Initialize
Initialize variables
Begin_flight
Age the aircraft and parts
Flight_length = lognormal(2.05,1)
Aircraft_age = Aircraft_age + Flight_length
P1_age = P1_age + Flight_length
Part degredation
(Determine P1_actual)
P1_actual = compare rand() to probability of failure (POF) graph at P1_age:
if(rand()>POF(P1_age), "G") else if(rand()>0.8*POF(P1_age),"Y"), else "R"
P1 = Part 1
if(P1_age>P1_exp, P1_reason = "PL“ and R=R+1), else if(P1_age>0.8*P1_exp, P1_reason =
Determine P1_assigned for "PL“ and Y = Y+1),else if (P1_actual="R", P1_reason = "FD“ and R = R+1), else if
"PL" = Predicted Life
Part 1
(P1_actual="Y", P1_reason = "FD“ and Y = Y+1), else "G"
"FD" = Fault Detection
Max_allowable = 2 for 5-part
Count "R","Y"
if( R > 0 or Y > Max_allowable, goto Mx_trip), else P1_notify="true" and goto Begin_flight systems
Mx_trip
Count notifictions
total_notifications = sum(Px_reason = "PL") + sum(Px_reason = “FD" and Px_notify="true") total_notifications
Count replaced parts
total_replaced = Sum(Px_assigned ="Y") + Sum(Px_assigned = "R")
Replace parts
Initialize variables for all Px_assigned = "Y" or "R"
End Mx_trip
goto Begin_flight
total_replaced
57
Mx as a fraction of operating expenses
58
Operating Expenses
SYS_FIELD
FIELD_DESC
Description
Expenses incurred directly in the in-flight operation of aircraft and expenses related to the
holding of aircraft and aircraft operational personnel in readiness for assignment for an inflight status. ( Air Carrier Financial Reports (Form 41 Financial Data) )
All expenses, both direct and indirect, specifically identifiable with the repair and upkeep of
MAINTENANCE 54000 - Maintenance
property and equipment. ( Air Carrier Financial Reports (Form 41 Financial Data) )
Cost of activities contributing to the comfort, safety, and convenience of passengers while in
55000 - Passenger
PAX_SERVICE
flight or when flights are interrupted. Includes salaries and expenses of flight attendants and
Service
passenger food expenses. ( Air Carrier Financial Reports (Form 41 Financial Data) )
Compensation of ground personnel, in-flight expenses for handling and protecting all nonpassenger traffic including passenger baggage, and other expenses incurred on the ground to
(1) protect and control the in-flight movement of the aircraft, (2) schedule and prepare
64000 - Aircraft And
AIRCFT_SERVICES
aircraft operational crew for flight assignment, (3) handle and service aircraft while in line
Traffic Servicing
operation, and (4) service and handle traffic on the ground after issuance of documents
establishing the air carrier's responsibility to provide air transportation. ( Air Carrier Financial
Reports (Form 41 Financial Data) )
Cost incurred in promoting the use of air transportation generally and creating a public
67000 - Promotion
preference for the services of particular air carriers. Includes the functions of selling,
PROMOTION_SALES
And Sales
advertising, and publicity, space reservations, and developing tarrifs and flight schedules for
publication. ( Air Carrier Financial Reports (Form 41 Financial Data) )
68000 - General And
GENERAL_ADMIN
Administrative
69000 - General And
GENERAL_SERVICES
Administrative
70000 - Depreciation
DEPREC_AMORT
And Amortization
71000 - Transport
All expense items applicable to the generation of transport-related revenues. ( Air Carrier
TRANS_EXPENSES
Related Expenses
Financial Reports (Form 41 Financial Data) )
FLYING_OPS
51000 - Flying
Operations
59
3.5
700
3
680
2.5
660
2
640
1.5
620
1
600
Direct Mx Flight Equipment (Adjusted for inflation)
Direct Mx Flight Equipment
Direct Maintenance cost per flight hour (adjusted for inflation)
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
560
1993
0
1992
580
1991
0.5
1990
Billions
Quarterly Direct Mx Expenses
60
Airworthiness Directives
Annual Count of Airworthiness Directives Issued
500
450
400
350
300
250
200
150
100
50
0
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
61
MEL Systems
1400
1194
1200
1000
800
600
Quantity of parts under under main systems (
number)
400
200
Cumulative
182
145
95
93
75
73
63
57
52
50
49
44
39
24
23
23
21
14
12
12
12
9
9
6
4
4
2
0
62
2
Regulatory Pressure
Millions
Total penalties assessed per quarter
9
8.4 M
8
Penalties assessed in millions USD
7
6
5
4
3.3 M
3
2
1
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
0
Year
FAA – Quarterly
Enforcement Reports
$3.9 Million: total of civil penalties for maintenance issues in the last year
$24.2 Million: FAA-proposed penalty for Airworthiness Directive noncompliance.
63