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Sponsored By:
Airline Fleet Readiness:Trade-off Analysis of Alternate Maintenance Systems
1
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
2
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
3
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Unstable Demand, Fluctuating Prices
$0.00
$50.00
$100.00
$150.00
$200.00
$250.00
$300.00
$350.00
$400.00
$450.00
$500.00
0
2
4
6
8
10
12
14
16
18
20
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
Nat
ion
al A
vera
ge T
icke
t Fa
re (
USD
)
Air
Car
rier
Op
erat
ion
s (M
illio
ns)
Year
Comparison of Air Traffic and Ticket Fare
4Source: FAA – ATADS and BTS
Average Ticket Fare
Air Carrier Traffic Operations
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-20
-10
0
10
20
30
40
501
99
0
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
Bill
ion
s (U
SD)
Year
Airline Profitability vs Time
Annual Profit
Cumulative Profit
Airline Profitability
: Recession (7/90-3/91, 3/01-11/01, 12/07-6/09)5
Source: BTS RITA Schedule 12 and NBER
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Total Operating Expenses
6
Source: BTS
Direct Maintenance (≈10% of Total)
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560
580
600
620
640
660
680
700
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
Co
st p
er F
ligh
t H
ou
r (U
SD)
Year
Direct Maintenance Cost per Flight Hour (Adjusted for Inflation)
3
4
5
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
Air
Ho
urs
(M
illio
ns)
Total Quarterly Air Hours
Increasing Maintenance Costs
7
2
2.5
3
3.52
00
3
20
04
20
05
20
06
20
07
20
08
20
09
20
10
Bill
ion
s (U
SD)
Quarterly Direct Maintenance Cost (Adjusted for Inflation)
Source: BTS RITA Schedule P-12
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In Service: Producing Revenue
Out for Maintenance: Losing Revenue and
Incurring Costs
Indirect Cost of Maintenance
8
Fleet Readiness: The percentage of time that a given aircraft is in service
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Low
erH
igh
er
Lower Higher
Maintenance Cost Gap
9
Co
st
Frequency of part replacement
Total Cost
Maintenance Costs (direct and indirect)
Other Operating Expenses
Current
Optimal
Goal:Reduce
Cost Gap
*Note: This figure is not drawn to scale.
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Aircraft Complexity
10Source: FlightGlobal and Boeing
“*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
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Aircraft Complexity
11
System# of sub-systems
Navigation 182
Air Conditioning 145
Fire Protection 95
Fuel 93
Communications 75
Doors 73
Lights 63
Equipment/Furnishings 57
Flight Controls 52
Ice and Rain Protection 50
All Others 309
Total: 1194
Boeing 737 Family
Source: Boeing and FAA – Boeing 737 MMEL
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
12
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Problem and Need Statements
13
560
580
600
620
640
660
680
700
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
Co
st (
USD
)
Year
Direct Maintenance Cost
Problem: Maintenance costs are increasing over time.
Need: Airline companies need to reverse the current trend of increasing maintenance costs.
Indirect Maintenance Cost
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Approach
14
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
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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
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
16
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Part Condition Tracking
Boeing 737 Family
Mx ActionsPerformed
Aircraft, Workshop and Enterprise
Levels
Part Replacement
Scope
17
Non- MxOperating Costs
Other Aircraft Makes and
Models
Mx = Maintenance
Time Spent on Each Mx Action
Outsourced Mx
Ticket Prices
FluctuatingDemand
Phased MxSchedules
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
18
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System Operational Scenario
19Mx = Maintenance
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Aircraft Workshop Enterprise
Primary StakeholdersSecondary Stakeholders
Affected by equipage changes and operational changes of personnel on each aircraft
Affected by changes in infrastructure, operations, and equipment that occur in the maintenance facility
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
Federal Aviation Administration (FAA)
X X X
Federal Communications Commission (FCC)
X
Maintenance, Repair, and Overhaul (MRO) Personnel
X X X
Occupational Safety and Health Administration (OSHA)
X
Tool and Part Manufacturers X X
Tool and Part Shipment Company X
Stakeholder Analysis
20
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Stakeholder Interaction Diagram
21
Aircraft
Passengers
Aircraft
Manufacturer
Competing
Airlines
Aircraft Flight
Crew
FAAFCC
Tool and Part
Manufacturer
MRO
Tool and Part
Shipping
Company
Airline Fleet
Operator
Airline Fleet
Owner
Maintenance
System
OSHA
Regulation and Oversight
Supply ChainRevenue
Enterprise
Workshop Aircraft
RegulationsWorkshop
Mx System
Enterprise
Supply
Revenue
Aircraft
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
22
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Design Alternatives
1. Hangar Transfer– Information is transferred in the
maintenance facility
– Preventative based
2. Flight Line Transfer– Information is transferred in
between each flight
– Condition based
3. Airborne Transfer– Information is transferred during
flight
– Condition based
23
B49
Maintenance Bay
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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
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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
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Alternative 1: Hangar Transfer
26Mx = Maintenance
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Alternative 2: Flight Line Transfer
27Mx = Maintenance
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Alternative 3: Airborne Transfer
28Mx = Maintenance
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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
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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
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
31
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Model Design
32Mx = Maintenance
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Green, Yellow, Red Assignments
33
Green
Yellow
Red
Replacement is not required
Replacement is required but immediate action is not necessary
Replacement is required at next landing
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Model Variables
34
Aircraft
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)
• Age of Aircraft (Flight Hours)
• Maintenance Trip Needed (Y,N)
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Propellors/Propulsors
Navigation
Air Conditioning
Lights
Flight ControlsLanding Gear
Equipment/Furnishings
Powerplant
Stabilizers
Doors
Wings
Fuselage
Nacels/Pylons
0.00001
0.0001
0.001
0.01
0.1
1
0 10000 20000 30000 40000 50000 60000 70000
Fre
qu
en
cy o
f D
iffi
cult
y
Age of Airframe (In Flight Hours) at Time of Difficulty
Comparison of Reported Difficulties
Data Input: Part Life and Selection
35
Mo
re F
req
ue
nt
Older Airframes
Source: FAA – SDR Database (737 only) *Note: Part selection is not yet finalized
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Data Input: Flight Length
36
––– Lognormal(2.05, 1.31)
Length of Flight (Hours)
Nu
mb
er
of
Flig
hts
Source: BTS RITA:Form T-100 data, Average Ramp-To-Ramp Times,2008-2010
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Logical System Model
37Mx = Maintenance
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AlternativeProbability of Part Failure
Predicted Life of Parts
Maximum Allowable
Yellow Parts
Number of Maintenance
Stops
Number of Parts Replaced
Number of Parts Replaced
WithNotification
Total Cost of Maintenance
Hangar Transfer (Preventative)
Low Estimate# hours (low) Infinity
# hours (high) Infinity
High Estimate# hours (low) Infinity
# hours (high) Infinity
Flight Line Transfer
(Condition)
Low EstimateInfinity # parts (low)
Infinity # parts (high)
High EstimateInfinity # parts (low)
Infinity # parts (high)
Airborne Transfer
(Condition)
Low EstimateInfinity # parts (low)
Infinity # parts (high)
High EstimateInfinity # parts (low)
Infinity # parts (high)
Design of Experiment
38
Input Output
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Utilities
39Mx = Maintenance *Note: Weights will be elicited by survey
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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
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Overview
1. Context
2. Problem and Need Statements
3. Scope
4. Stakeholder Analysis
5. Design Alternatives
6. Method of Analysis
7. Project Schedule
41
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Project Schedule
42*Task is on Critical Path
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Performance and Projected Cost
43
$37,875
0
5000
10000
15000
20000
25000
30000
35000
40000
5-S
ep
12
-Sep
19
-Sep
26
-Sep
3-O
ct
10
-Oct
17
-Oct
24
-Oct
31
-Oct
7-N
ov
14
-No
v
21
-No
v
28
-No
v
5-D
ec
12
-Dec
19
-Dec
26
-Dec
2-J
an
9-J
an
16
-Jan
23
-Jan
30
-Jan
6-F
eb
13
-Feb
20
-Feb
27
-Feb
6-M
ar
13
-Mar
20
-Mar
27
-Mar
3-A
pr
10
-Ap
r
Co
st (
USD
)
Week
Earned Value
Budgeted Cost
Actual Cost
Work Performed
*Note: $50/hour (loaded rate)757.5 hours total
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CPI and SPI
44CPI = Cost Performance IndexSPI = Schedule Performance Index
*Note: Index of 1.00 is performing as expected
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
5-S
ep
12
-Sep
19
-Sep
26
-Sep
3-O
ct
10
-Oct
17
-Oct
24
-Oct
31
-Oct
7-N
ov
14
-No
v
21
-No
v
28
-No
v
5-D
ec
12
-Dec
19
-Dec
26
-Dec
2-J
an
9-J
an
16
-Jan
23
-Jan
30
-Jan
6-F
eb
13
-Feb
20
-Feb
27
-Feb
6-M
ar
13
-Mar
20
-Mar
27
-Mar
3-A
pr
10
-Ap
r
Ind
ex
Week
CPI and SPI
CPI
SPI
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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
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Questions?
?
46
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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
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Model
49
Discrete Event System Model
Probability of Part Failure
Maximum Allowed “Yellow” Parts
Predicted Life of Part
Inputs Outputs
Number of Maintenance Actions
Number of Parts Replaced
Average Lead Time Before Repair
Total Cost of Maintenance
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Failure Patterns
50
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Failure Patterns
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
UAL Broberg MSP SUB
Bathtub
Exponential
Linear
Log
Flat
Decay
51
Aviation Naval
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Stakeholder Node Adjacency Matrix
52
Node
Airline Fleet
Operator
Airline Fleet
Owner
Aircraft
Flight Crew
Aircraft
Manufacturer
Aircraft
Passengers
Maintenance
System
Competing
AirlinesFAA FCC MRO OSHA
Tool and Part
Manufacturer
Tool and Part
Shipping
Company
Airline Fleet
OperatorSchedules
Maintenance
Reports
Ticket Price
Competition
Airline Fleet
OwnerBudget
Cost of
Construction,
Capabilities
Budget
Aircraft Flight
CrewLabor Cost Labor cost
Aircraft
Manufacturer
Cost of
Construction
Aircraft
Passengers
Need for
Fewer
Delays
Revenue Ticket Sales
Procedures,
Airworthines
s Directives
Maintenance
System
Fleet
Operations
Down Time,
Schedule
CostSchedules,
Procedures
Trend
feedback,
Changes in
Equipment
DelaysDivergent
Practices
System
Interfaces,
Additional
Training,
Procedures
Inventory
Requirements
Need for Fast
Shipping
Competing
AirlinesTicket Prices
Price
Competition
FAA Regulations Regulations Regulations Regulations Regulations Certifications
FCC Regulations Regulations Regulations
MRO Labor Cost
Need for
Reliable
Shipping
OSHASafety
Regulations
Safety
Regulations
Tool and Part
Manufacturer
Tools and
Parts
Tool and Part
Shipping
Company
Shipping
Costs
Shipping
Costs
Tools and
Parts
To
Fro
m
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Service Difficulty Reports
53
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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
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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
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Logical System Model (Expanded)
56
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System Model (Pseudo Code)
57
Action Formula
Initialize Initialize variables
Begin_flight
Age the aircraft and parts
Flight_length = lognormal(2.05,1)Aircraft_age = Aircraft_age + Flight_lengthP1_age = P1_age + Flight_length P1 = Part 1
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"
Determine P1_assigned for Part 1
if(P1_age>P1_exp, P1_reason = "PL“ and R=R+1), else if(P1_age>0.8*P1_exp, P1_reason = "PL“ and Y = Y+1),else if (P1_actual="R", P1_reason = "FD“ and R = R+1), else if (P1_actual="Y", P1_reason = "FD“ and Y = Y+1), else "G"
"PL" = Predicted Life"FD" = Fault Detection
Count "R","Y" if( R > 0 or Y > Max_allowable, goto Mx_trip), else P1_notify="true" and goto Begin_flightMax_allowable = 2 for 5-part 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") total_replaced
Replace parts Initialize variables for all Px_assigned = "Y" or "R"
End Mx_trip goto Begin_flight
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Mx as a fraction of operating expenses
58
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Operating Expenses
59
SYS_FIELD FIELD_DESC Description
FLYING_OPS51000 - Flying Operations
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 in-flight status. ( Air Carrier Financial Reports (Form 41 Financial Data) )
MAINTENANCE 54000 - Maintenance All expenses, both direct and indirect, specifically identifiable with the repair and upkeep of property and equipment. ( Air Carrier Financial Reports (Form 41 Financial Data) )
PAX_SERVICE55000 - Passenger Service
Cost of activities contributing to the comfort, safety, and convenience of passengers while in flight or when flights are interrupted. Includes salaries and expenses of flight attendants and passenger food expenses. ( Air Carrier Financial Reports (Form 41 Financial Data) )
AIRCFT_SERVICES64000 - Aircraft And Traffic Servicing
Compensation of ground personnel, in-flight expenses for handling and protecting all non-passenger 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 aircraft operational crew for flight assignment, (3) handle and service aircraft while in line 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) )
PROMOTION_SALES67000 - Promotion And Sales
Cost incurred in promoting the use of air transportation generally and creating a public preference for the services of particular air carriers. Includes the functions of selling, advertising, and publicity, space reservations, and developing tarrifs and flight schedules for publication. ( Air Carrier Financial Reports (Form 41 Financial Data) )
GENERAL_ADMIN68000 - General And Administrative
GENERAL_SERVICES69000 - General And Administrative
DEPREC_AMORT70000 - Depreciation And Amortization
TRANS_EXPENSES71000 - Transport Related Expenses
All expense items applicable to the generation of transport-related revenues. ( Air Carrier Financial Reports (Form 41 Financial Data) )
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Quarterly Direct Mx Expenses
60
560
580
600
620
640
660
680
700
0
0.5
1
1.5
2
2.5
3
3.5
19
90
19
91
19
92
19
93
19
94
19
95
19
96
19
97
19
98
19
99
20
00
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
Bill
ion
s
Direct Mx Flight Equipment (Adjusted for inflation)Direct Mx Flight EquipmentDirect Maintenance cost per flight hour (adjusted for inflation)
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Airworthiness Directives
61
0
50
100
150
200
250
300
350
400
450
500
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Annual Count of Airworthiness Directives Issued
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MEL Systems
62
182145
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 2
1194
0
200
400
600
800
1000
1200
1400
Quantity of parts under under main systems ( number)
Cumulative
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Regulatory Pressure
$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
FAA – Quarterly Enforcement Reports
3.3 M
8.4 M
0
1
2
3
4
5
6
7
8
92
00
0
20
01
20
02
20
03
20
04
20
05
20
06
20
07
20
08
20
09
20
10
Pe
nal
tie
s as
sess
ed
in m
illio
ns
USD
Mill
ion
s
Year
Total penalties assessed per quarter