airliner fuel conservation
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8/9/2019 Airliner Fuel Conservation
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Fuel Conservation
Dave AndersonPerformance Engineering OperationsFlight Operations Engineering
Boeing Commercial AirplanesOctober 2006
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2Fuel Conservation
Why Fuel Conservation?
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3Fuel Conservation
What is Fuel Conservation?
Fuel conservation means managing the
operation and condition of an airplane tominimize the fuel used on every flight
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4Fuel Conservation
*Assumes typical airplane utilization rates
How Much Is A 1% Reduction In Fuel Worth?
Airplane Fuel savings*
type gal/year/airplane777 70,000 90,000
767 30,000 40,000
757 25,000 35,000
747 100,000 135,000
737 15,000 25,000
727 30,000 40,000
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5Fuel Conservation
How Much Is This Worth In $$?
Depends on Current Fuel Prices!
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$0.00
$0.20
$0.40
$0.60
$0.80
$1.00
$1.20
$1.40
$1.60
$1.80
$2.00
$2.20
87 89 91 93 95 97 99 01 03 05
Jet Fuel Prices
Year
$ / g a
l l o n
Source: Air Transport World
$0.60
$2.00
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Airplane Fuel savings Fuel savings*
type gal/year/airplane $/year/airplane
*Assumes $2.00/gallon
How Much Is A 1% Reduction In Fuel Worth?
777 70,000 90,000 $140,000 180,000
767 30,000 40,000 $60,000 80,000
757 25,000 35,000 $50,000 70,000
747 100,000 135,000 $200,000 270,000
737 15,000 25,000 $30,000
50,000727 30,000 40,000 $60,000 80,000
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What Is Fuel ConservationFrom An Airline Business Viewpoint ?
Fuel conservation means managing the
operation and condition of an airplane tominimize the fuel used on every flight
total cost of total cost of
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Total savings =fuel savings
- cost toimplement
Cost to Total Cost
Implement Savings/AP
?? ??
Airplane Fuel savings Fuel savings*
type gal/year/airplane $/year/airplane
How Much Is A 1% Reduction In Fuel Worth?
777 70,000 90,000 $140,000 180,000
767 30,000 40,000 $60,000 80,000
757 25,000 35,000 $50,000 70,000
747 100,000 135,000 $200,000 270,000
737 15,000
25,000 $30,000
50,000727 30,000 40,000 $60,000 80,000
*Assumes $2.00/gallon
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Reducing Fuel Costs Requires Everyone’s Help
• Flight Operations
• Dispatchers
• Flight Crews
• Maintenance
• Management• Fuel Purchasing (Contracts)
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FLIGHT
OPERATIONS
ENGINEERING
Operational Practicesfor Fuel Conservation
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Flight Operations / Dispatchers
• Reduce Landing Weight
• Load Proper Fuel Reserves
• Load Airplane at Aft C.G.
• Select Minimum Flap that Meets allRequirements
• Fly Optimum Altitudes
• Plan and Fly Efficient Speeds
• Select Shortest Route
• Use Fuel Tankering if Cost Effective
Opportunities For Fuel Conservation
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Reduced Landing Weight
1% reduction in landing weight produces:
≅ 0.75% reduction in trip fuel (high BPR engines)
≅ 1% reduction in trip fuel (low BPR engines)
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Required AdditionalWLDG = OEW + Payload + reserve + fuel loaded
fuel but not used
Zero fuel weightZero fuel weight
Fuel on board at landingFuel on board at landing
Components Of Landing Weight
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% Block Fuel Savings Per 1000 Lb(454 Kg) ZFW Reduction
737-3/4/500
737-6/7/8/900
757-200/300
767-2/3/400
777-200/300 747-400
.7% .6% .5% .3% .2% .2%
717-200
.9%
Reducing ZFW Reduces Landing Weight
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Reducing OEW Reduces Landing Weight
• Passenger service items
• Passenger entertainment items
• Empty Cargo and baggage containers
• Unneeded Emergency equipment• Excess Potable water
Items To Consider
R d i U F l
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Reducing Unnecessary FuelReduces Landing Weight
• Practice cruise performance monitoring
• Flight plan by tail numbers
• Reduce discretionary fuel
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Fuel Reserves
• Carry the appropriate amount of reserves to ensure
a safe flight and to meet your regulatory requirements
• Extra reserves are extra weight
• Airplane burns extra fuel to carry the extra weight
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19Fuel Conservation
Fuel Reserves
The amount of required fuel reserves depends on:
• Regulatory requirements
• Choice of alternate airport
• Use of re-dispatch
• Company policies on reserves
• Discretionary fuel
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20Fuel Conservation
Regulatory Requirements
• Is this an international flight?
• FAA rules?
• ICAO rules?
• Other rules?
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21Fuel Conservation
FAA “International Reserves”
(A) To fly to and land at the airport to which it is released;
(B) After that, to fly for a period of 10 percent of the total time required to fly from theairport of departure to, and land at, the airport to which it was released;
(C) After that, to fly to and land at the most distant alternate airport specified in theflight release, if an alternate is required; and
(D) After that, to fly for 30 minutes at holding speed at 1,500 feet above the alternateairport (or the destination airport if no alternate is required) under standardtemperature conditions.
FAR 121.645(b)
DC
B
A
ContingencyContingency
AlternateAlternate
HoldingHolding
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22Fuel Conservation
FAA “Island Reserves”
• No alternate is specified in release under Section121.621(a)(2) or Section 121.623(b).
• Must have enough fuel, considering wind and otherweather conditions expected, to fly to destinationairport and thereafter to fly for 2 hours at normal
cruising fuel consumption
FAR 121.645(c)
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23Fuel Conservation
ICAO International
4.3.6.3.1 When an alternate aerodrome is required;
To fly to and execute an approach, and a missed approach,at the aerodrome to which the flight is planned, and
thereafter:
A) To fly to the alternate aerodrome specified in theflight plan; and then
B) To fly for 30 minutes at holding speed at 450 M
(1,500 ft) above the alternate aerodrome under standardtemperature conditions, and approach and land; and
C) To have an additional amount of fuel sufficient toprovide for the increased consumption on the occurrenceof any of the potential contingencies specified by theoperator to the satisfaction of the state of the operator(typically a percentage of the trip fuel: 3% to 6%).
CA
B
ContingencyContingency
HoldingHolding
AlternateAlternate
ICAO Annex 6 (4.3.6.3)
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24Fuel Conservation
Alternate Airport
What items should you consider when choosingan alternate airport?
• Airline facilities
• Size and surface of runway
• Weather
• Hours of operation, lighting
• Fire fighting, rescue equipment
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25Fuel Conservation
Alternate Airport
What items should you consider when choosingan alternate airport?
• Airline facilities
• Size and surface of runway
• Weather
• Hours of operation, lighting
• Fire fighting, rescue equipment
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26Fuel Conservation
Speed Selection for Holding
• Want to maximize time per kilogram of fuel
• Use published/FMC recommended holdingspeeds
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27Fuel Conservation
Use Redispatch to Lower Contingency Fuel
• Reserve/contingency fuel is a function of trip lengthor trip fuel burn
• Originally implemented to cover errors in navigation,weather prediction, etc...
• Navigation and weather forecasting techniques haveimproved, decreasing the chance that contingencyfuel will actually be used
• FAR 121.631 allows dispatch to an airport short of
the intended destination with enroute re-clearance.The conditions of FAR 121.645 must be met at thetime of redispatch with fuel for 10% of the flight timefrom the redispatch point to the destination
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28Fuel Conservation
How Redispatch Works
Climb
Descent
Cruise
Intendeddestination
Origin
Redispatch
point
Initialdestination
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29Fuel Conservation
IntendeddestinationOrigin
Intended
destinationOrigin
Redispatchpoint
Initialdestination
Redispatch
point
Initialdestination
Off Track Initial Destination
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30Fuel Conservation
Fuel Savings
Distance (Time)
Redispatch
point
C o n t i n g e n c
y f u e l
Fuel required
Intendeddestination
Reduction incontingencyfuel required
at landing
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31Fuel Conservation
Benefits of Redispatch
Reduced fuel load
Increased payload
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32Fuel Conservation
B
Initialdestination
A
Origin
C
Finaldestination
Examples of Using Redispatch
To: 1) Increase payload
2) Decrease takeoff and landing weight(by reducing fuel load)
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33Fuel Conservation
Example of payloadincrease with constant
takeoff weight
OEW
PAYLOAD(1)
Altern+ HoldContingency
TRIPFUEL
TRIPFUEL
Same takeoff weight with andwithout redispatch
O p t i m
u m
r e d i s p
a t c h p
o i n t
A C
OEW
A B
(No redispatch)
PAYLOAD(2)
Altern+ HoldContingency
PAYLOAD(2)
Redispatch Point C
OEW
TRIP FUEL
Altern+ Hold Contingency
Gross
weight
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34Fuel Conservation
Example of takeoffweight and landing
weight decreases with
constant payload
OEW
PAYLOAD(1)
Altern+ HoldContingency
TRIPFUEL
TRIPFUEL
O p t i m
u m
r e d i s p
a t c h p
o i n t
A C
(No redispatch)
A B Redispatch Point C
OEW
PAYLOAD(2)
PAYLOAD(2)
OEW
TRIP FUEL
Altern+ HoldContingency Contingency Altern+ Hold
Takeoff weight decrease
Landing
weight (1)
L a n d i n g
w e i g h t ( 2 )
( d e c r e a s
e f r o m
( 1 ) )
Gross
weight
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35Fuel Conservation
WT (fwd c.g.)Lift tail (fwd c.g.)
Lift wing (fwd c.g.)
• At aft c.g. the lift of the tail is less negative than at forwardc.g. due to the smaller moment arm between Liftwing and WT
• Less angle of attack, α, is required to create the lower Liftwing
required to offset the WT plus the less negative Lifttail
• Same Lifttotal, but lower Liftwing and therefore lower α required
Lift wing (aft c .g.)
WT (aft c.g.)
Lift tail (aft c.g.)
<
= Is less negative than
Airplane Loading
Maintain C.G. In The Mid To Aft Range
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36Fuel Conservation
737-700 777-200
• Actual variation in drag due to c.g. depends on airplanedesign, weight, altitude and Mach
Airplane Loading (continued)
• Simplified examples of change in drag due to c.g. can befound in the various Performance Engineer’s Manuals
Maintain c.g. in the Mid to Aft Range
.84M trim drag
CG range
14% to 19%
19% to 26%
26% to 37%
37% to 44%
∆CD trim
+2%
+1%
0
-1%
.78M trim drag
CG range
8% to 12%
13% to 18%
19% to 25%
26% to 33%
∆CD trim
+2%
+1%
0
-1%
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37Fuel Conservation
Flap Setting
Choose lowest flap setting that will meet takeoffperformance requirements:
• Less drag• Better climb performance
• Spend less time at low altitudes, burn less fuel
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38Fuel Conservation
Altitude Selection
Pressure altitude for a given weight and speed
schedule that produces the maximum air miles perunit of fuel
Optimum Altitude Definition
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39Fuel Conservation
Definition of Optimum Altitude
FUEL MILEAGE (NAM/LB)
P
R E S S U R E A L T
I T U D E ( 1 0 0 0 F
T )
0.024 0.028 0.032 0.036 0.040 0.044 0.048
30
32
34
36
38
40
GROSS WT
(1000 LB)
620
580
540
500
460420 380 340
300
O P T I M U M
(CONSTANT MACHNUMBER)
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40Fuel Conservation
LRC Mach
Determining Optimum Altitude
Cruise weight (1000 KG)
Brake release weight (1000 KG)
45
40
35
30 7060 9080 110100 120
70 80 90 100 110 120
Pressurealtitude
(1000 ft)
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41Fuel Conservation
Step Climb
= Off optimum operations
Optimum Altitude
4000 ft
2000 ft
Stepclimb
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42Fuel Conservation
O p t i m
u m a l t
i t u d e
+ 1.5%
+ 1.5%
1000 ft
+ 0.5%
+ 3.0%
+ 0.5%
+ 6.5%
+ 1.5%
+ 8.5%
4-hour Average = + 4.8%
+ 0%
+ 4.5%
4-hour Average = + 0.6%
Off-Optimum Fuel Burn Penalty
4000 ft Step vs. No Step Over a 4-Hour Cruise(Example Only)
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43Fuel Conservation
Speed Selection
NAM/poundfuel
MACH number
0.12
0.11
0.10
0.09
0.08
0.07
0.06
0.60 0.64 0.68 0.72 0.76 0.80 0.84
0.05
Increasingweight
LRC
MMO
MRC = Maximum range cruiseLRC = Long Range cruise
1%
LRC Versus MRC
MRC
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44Fuel Conservation
Speed Selection (continued)
• LRC = MRC + 1% fuel burn
• Significant speed increase for onlya 1% decrease in fuel mileage
• Increases speed stability
• Minimizes throttle adjustments
LRC Versus MRC
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45Fuel Conservation
0
1
2
3
4
5
6
7
8
0.00 0.01 0.02 0.03 0.04
∆ Mach from MRC
∆ F
u e l ~
%
-30
-25
-20
-15
-10
-5
0
0.00 0.01 0.02 0.03 0.04
∆ Mach from MRC
∆ T
i m e ~ m i n .
LRC
Aircraft Type 1
L R
C ( a / c 1 )
L R
C ( a / c 2 )
Fuel For Flying Faster Than MRC
Flying Faster Than LRC?
5000 NM cruise
Time For Flying Faster Than MRC
Aircraft Type 1
AircraftType 2
AircraftType 2
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46Fuel Conservation
Speed Selection - Other Options
• Cost Index = 0 (maximize ngm/lb
= wind-adjusted MRC)• Selected Cost Index (minimize costs)
• Maximum Endurance (maximize time/lb)
CI = Time cost ~ $/hr Fuel cost ~ cents/lb
High CI high speed, high trip fuel, low trip timeLow CI low speed, low fuel burn, high trip time
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47Fuel Conservation
Route Selection
Choose the most favorable route available
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48Fuel Conservation
Great Circle
• Shortest ground distance between 2 points on theearth’s surface
• May not be the shortest time when winds areincluded
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49Fuel Conservation
ETOPS
• ETOPS allows for more direct routes
• Shorter routes = less fuel required
New York
Montreal
St. Johns
Goose Bay
IqaluitKangerlussuaq
Reykjavik
Shannon Paris
1 2 0 m i n
6 0 m i n
31 4 8
3 4 6 1
Using 120 min ETOPS leads to
a 9% savings in trip distance!
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50Fuel Conservation
Fuel Tankering
Fuel tankering is the practice of carrying
more fuel than required for a particularsector in order to reduce the quantity offuel loaded at the destination airport forthe following sector (or sectors)
What Is It?
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51Fuel Conservation
A B C
Leg 1 Leg 2
Reserves
Fuelfor
leg 2
Fuelfor
leg 2
Fuelfor
leg 1
Fuelfor
leg 1
Fuel loaded at A for leg 1Fuel loaded at
B for leg 2
No tankeringof 2nd leg fuel
Reserves
Extra fuel burnedon leg 1 to carry
fuel for leg 2 Fuelfor
leg 2
Fuelfor
leg 2
Fuelfor
leg 1
Fuelfor
leg 1
100% tankeringof 2nd leg fuel
Fuel loadedat A for legs 1 & 2
Fuel Tankering (continued)
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52Fuel Conservation
Reduction in total fuel costs for multiple legflights is usually the main reason for tankering
Reduction in total fuel costs for multiple legflights is usually the main reason for tankering
Fuel Tankering (continued)
• Shorter turnaround time
• Limited amount of fuel available• Unreliable airport services
• Fuel quality at destination airport
• Fuel price differential
Why Tanker Fuel?
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53Fuel Conservation
Fuel Tankering (continued)
• If price at departure airport is sufficiently less than at thedestination airport, surplus fuel could be carried fromthe departure airport to lower the total fuel cost
• Fuel used increases on flights where fuel is tankeredsuch that the quantity of fuel available at landing is
always less than what was originally loaded (oftencalled ‘surplus fuel burn-off’)
• Surplus fuel burn-off must be accounted for in any pricedifferential calculation
• To be cost-effective, the difference in fuel price betweenthe departure and destination airports must be largeenough to offset the cost of the additional fuel burned
in carrying the tankered fuel
Fuel Price Differential
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54Fuel Conservation
Fuel Tankering (continued)
• The amount of tankered fuel loaded may
be limited by: – Certified MTOW
– Performance-limited MTOW
– Certified MLW – Performance-limited MLW
– Fuel capacity
• These limits must always be checked whenloading extra fuel for tankering!
Limitations On Total Amounts
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55Fuel Conservation
Difficult to quantify, but should be
addressed in all cost calculations
Fuel Tankering (continued)
• Lowers initial cruise altitude capability
• Increases takeoff weight: higher takeoff speeds,less reduced thrust, may require improved climb
• If landing is planned at or near MLW, and additional
fuel burn-off was over-predicted, an overweightlanding could result
• Higher maintenance costs: engines, reversers,wheels, tires, brakes
Additional Considerations
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56Fuel Conservation
To Tanker or Not to Tanker
• Cost calculations vary between operators, ranging
from the fairly simple to the fairly complex
• Complexity of the calculations depends on therequirements of your operations. (e.g., If the
decision to tanker is made by the captain at thetime of fueling, a simple method is desired)
• Many operators add a price per gallon, or a fixed
percentage, to cover increased maintenance costs
Cost Calculations
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57Fuel Conservation
Cost Calculations
We will briefly review 3 possible methods:
1) Assumed percentage burn-off
2) Break-even price ratio
3) Relative cost to tanker
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58Fuel Conservation
Cost Calculations (continued)
• All methods should begin by checking whether
takeoff and landing weight limits, along with fuelcapacity limits, allow additional fuel to be loaded
• Some operators choose a minimum tankering
amount such that if the amount available to tankeris not at least equal to their chosen minimum,no fuel will be tankered
C C l l i ( i d)
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59Fuel Conservation
Cost Calculations (continued)
Calculation of fuel prices is not always as easyas it first appears. Understand how fuel prices are
determined at your airline.
For example:
• Price may vary with amount purchased
• Fixed hookup fees should be included (affectsprice per gallon - as more fuel is purchased,the hookup price/gallon decreases)
• Taxes charged may be returned later as taxrebates lower the price per gallon
‘A d P t B ff’ M th d
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60Fuel Conservation
‘Assumed Percentage Burn-off’ Method
• Assumes a fixed percentage of the tankered fuelis consumed per hour of flight time; usually 4 to 5%per hour
• Divide total cost of additional fuel purchasedat departure airport by amount remaining atdestination airport to determine ‘effective’ price
of fuel at destination
• Assume some per gallon cost to cover unknowns
• Break-even price is the ‘effective’ price plus theallowance for unknown costs
• If price of fuel at destination is above the breakeven
price, then it is cost-effective to tanker
E l C t C l l ti
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61Fuel Conservation
Example Cost Calculation
• Planned flight time = 6 hours
• Departure fuel price = $1.00/gallon
• Tankered fuel loaded = 40000 lb (6000 gallons)
• Cost of tankered fuel = $6000
• Surplus fuel burn-off (4%/hour) = 24%
• Tankered fuel at landing = 6000 x .76 = 4560 gallons
• Effective cost of tankered fuel = 6000/4560 = $1.32/gal
• Allowance for unknown cost = $.02/gal (typical?)• Actual cost of tankered fuel = $1.32 + $.02 = $1.34/gal
• Cost-effective if destination fuel price above $1.34/gal
B k E P i R ti M th d
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62Fuel Conservation
Trip distance (nm) Break-even price ratio
200
400
600
8001000
2000
3000
4000
5000
6000
1.012
1.023
1.034
1.0461.061
1.130
1.217
1.334
1.495
1.722
S a m p l e d a t a
o n l y
v a r i e s
w i t h
a i r p
l a n e m o d
e l
S a m p l e d a t a
o n l y
v a r i e s
w i t h
a i r p
l a n e m o d
e l
• To economically justify tanker operation, the fuel
price at the destination must be greater than thebreak-even fuel price
Break-Even Price Ratio Method
• Method used in FPPM (found in chapter 2 text)• Break-even price ratio is presented as a function
of trip distance only
B k E P i R ti M th d ( ti d)
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63Fuel Conservation
$ * (tankered fuel) = $ * (tankered fuel - fuel burnoff)gal gal
Orig Dest = tankered fuelremaining at dest
Break-evenprice ratio
Orig
$gal Dest
B.E.
$gal *=Break-even price =
at destination
Break-Even Price Ratio Method (continued)
• Break-even fuel price is the destination price at which thecost of purchasing the fuel at the destination is equivalentto the cost of purchasing the same amount of fuel, plusthe fuel required to carry it, at the origin
• Break-even price occurs when:
B k E P i R ti M th d ( ti d)
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64Fuel Conservation
Break-Even Price Ratio Method (continued)
• If the destination fuel price is greater than the break-
even price, then it’s cheaper to tanker the fuel
• The break-even price ratio does not include anyallowance for additional maintenance costs; it only
considers the extra fuel burn off
E l C t C l l ti
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65Fuel Conservation
Example Cost Calculation
Fuel price at origin: $0.80/gal
Model: 737-700/CFM56-7B24Trip distance: 2000 NM
Trip distance, nm Break-even price ratio
200
400600800
1000200030004000
1.015
1.0311.0451.0591.0751.1751.3111.477
Break-even price = $0.80 ( 1.175) = $0.94
If dest. fuel price > $0.94, then more economical to tanker the fuelIf dest. fuel price < $0.94, then more economical to purchase at dest.
To include increased maintenance costs, should increase the B.E.
fuel price by the estimate (e.g., if unknown costs estimated at$0.02/gal, then B.E. fuel price = $0.94 + $0.02 = $0.96)
‘R l ti C t t T k ’ M th d
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66Fuel Conservation
‘Relative Cost to Tanker’ Method
• Considers the difference in total cost between
tankering and not tankering the fuel
• Only includes costs related to tankering or nottankering fuel
• Requires calculation of fuel required for actualroutes with and without tankering
‘Relative Cost to Tanker’ Method (continued)
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67Fuel Conservation
A B C
Leg 1 Leg 2
gal A
$ Fuelreq’dleg 1
Fuelcarriedfor usein leg 2
+Extra fuelburned on
leg 1 due toextra wt
+ + Additionalincrementalcosts due tohigher weight
galB
$+
Additionalfuel req’dfor leg 2
*
total cost with tankering
-gal
B
$Fuelreq’dleg 1
-gal
A
$ Fuelreq’dleg 2
**
Total cost with no tankering
‘Relative Cost to Tanker’ Method (continued)
‘Relative Cost to Tanker’ Method (continued)
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68Fuel Conservation
cost of tankering the fuel cost of purchasingat the destination
galB
$fuelcarriedfor usein leg 2
+
extra fuelburned on
leg 1 due toextra weight
+
additionalincrementalcosts due to
higher weight
- *gal
A
$fuel
carriedfor usein leg 2
‘Relative Cost to Tanker’ Method (continued)
Relative cost to tanker =
‘Relative Cost to Tanker’ Method (continued)
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69Fuel Conservation
• If relative cost to tanker = 0, then breakeven
• If relative cost to tanker > 0, then costs are increasedby tankering
• If relative cost to tanker < 0, then costs are reducedby tankering
• Some operators choose a minimum financial gain belowwhich there will not be tankering. (e.g., if minimum gainselected as $100, then tankering will only be used if
relative cost to tanker < - $100)
• Multiple legs (3 or more) add significantly to the complexityof the analysis
Relative Cost to Tanker Method (continued)
‘Relative Cost to Tanker’ Method (continued)
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70Fuel Conservation
Additional Applications
• If fuel is tankered in order to obtain a shorter turnaround
time at a given destination you can determine therelative cost of the shorter turnaround time
• Cost to tanker can be used to provide flight crews
with information on the cost of carrying additional,discretionary fuel
Relative Cost to Tanker Method (continued)
Fuel Tankering
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71Fuel Conservation
Fuel Tankering
• Most flight planning services offer tankering
analyses to their customers
• You can work with your flight planning service onwhich assumptions to use/include, and in what form
the results should be reported
Flight Crew
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72Fuel Conservation
Flight Crew
Opportunities for Fuel Conservation:
• Practice fuel economy in each phase of flight
• Understand the airplane’s systems - SystemsManagement
Engine Start
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73Fuel Conservation
Engine Start
• Start engines as late as possible, coordinatewith ATC departure schedule
• Take delays at the gate if possible
• Minimize APU use if ground power available
Taxi
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74Fuel Conservation
Taxi
• Take shortest route possible
• Use minimum thrust and minimum braking
• Taxi with all engines operating?
Taxi
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75Fuel Conservation
Taxi
• After-start and before-takeoff checklists delayed
• Reduced fire protection from ground personnel• High weights, soft asphalt, taxi-way slope
• Engine thermal stabilization - warm up and cool down
• Pneumatic and electrical system requirements
• Slow/tight turns in direction of operating engine(s)
• Cross-bleed start requirements
Balance fuel conservation and safety considerations
One Engine Shut Down Considerations
Sample Taxi and APU Fuel Burns
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76Fuel Conservation
Condition 727 737 747 757 767 777
Taxi(lb/min)
60 25 100 40 50 60
APU(lb/min)
5 4 11 4 4 9
717
25
4
Sample Taxi and APU Fuel Burns
Takeoff
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77Fuel Conservation
Takeoff
• Retract flaps as early as possible
(but, no lower than the minimum
recommended flap retraction height)
• Full rate or derate to save fuel?
Reduced Take Off ThrustImproves Performance Retention
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78Fuel Conservation
-1.0%
-0.9%
-0.8%
-0.7%
-0.6%
-0.5%
-0.4%
-0.3%
-0.2%
-0.1%
0.0%
-25% -20% -15% -10% -5% 0%
Average takeoff thrust reduction (% from full rate)
∆
T S F C @ 1
0 0 0 c y c l e s
Estimated Reduced ThrustImpact at 1000 Cycles
15% Average Thrust Reduction Can Improve
TSFC at 1000 Cycles by over 0.4%
(Courtesy of Pratt & Whitney)
Improves Performance Retention
Climb
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79Fuel Conservation
Distance
Altitude
Initial cruisealtitude
Cost index
increasing
A
B
C I = 0
( M
i n f u e l )
M i n t
i m e t
o P o i n t
B
M a x
g r a
d i e
n t
Climb
Cost Index = 0 minimizes fuel to climb andcruise to a common point in space
Cruise
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80Fuel Conservation
Cruise
• A plane flying in steady, level flight may requiresome control surface inputs to maintain lateral-directional control
• Use of the proper trim procedureminimizes drag
• Poor trim procedure canresult in a 0.5% cruisedrag penalty on a 747
• Follow the proceduresprovided in the FlightCrew Training Manual
Lateral - Directional Trim Procedure
Cruise
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81Fuel Conservation
Systems Management
Cruise
• A/C packs in high flow typically produce
a 0.5 - 1 % increase in fuel burn
• Do not use unnecessary cargo heat
• Do not use unnecessary anti-ice
• Maintain a balanced fuel load
Cruise
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82Fuel Conservation
Winds
Cruise
• Wind may be a reason to choose an “offoptimum” altitude
• Want to maximize ground miles per unitof fuel burned
• Wind-Altitude trade tables are providedin the operations manual
Wind Effects On Fuel Mileage
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83Fuel Conservation
Fuel Mileage = =Fuel Flow
VTAS
KG
NAM
Fuel Used = =
NGM/KG
NGM
NAM/KG
NAM
=
VTAS + VWIND
(NGM) (Fuel Flow)
Ground Fuel Mileage = =Fuel Flow
VTAS + VWIND
KG
NGM
In cruise: positive wind = Tailwind
negative wind = Headwind
V G r o u n d
Wind Effects On Fuel Mileage
Wind Effects On Cruise Altitude: Wind/Alt Trade
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84Fuel Conservation
777-200ER/PW4090 Example
Wind Effects On Cruise Altitude: Wind/Alt Trade
33 knots greater tailwind (or,lower headwind) would be
required at FL310 relative toFL350 to obtain equivalent
ground fuel mileage
Wind Effects On Cruise Altitude: Wind/Alt Trade
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85Fuel Conservation
MACH number
G
r o u n d f u e l m i l e
a g e
.80 .81 .82 .83 .84 .85 .8664
66
68
70
72
74
76
78
35 K , W i nd = 0
3 1K , W i nd = 0
MACH number
G r o u n d f u e l m i l e a g e
.80 .81 .82 .83 .84 .85 .8664
66
68
70
72
74
76
78
35K , W ind = 0
3 1K , W i nd = 0
W i nd = 10
W i nd = 2 0
W i nd = 3 0
W i nd = 4 0
LRC, 35K
777-200 / PW4090Ground fuel mileage, nm/1000 kg
Weight = 220,000 kg
Example of increasing Tailwind at 31,000 ft Example of increasing headwind at 35,000 ft
LRC, 31K
LRC, 31K
LRC, 35K
W i nd = - 10
W i nd = - 2 0
W ind = - 30
W i nd = - 4 0
Wind Effects On Cruise Altitude: Wind/Alt Trade
Wind Effects On Cruise Mach Number
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86Fuel Conservation
MACH number
G r
o u n d f u e l m i l e a g e
.74 .76 .78 .80 .82
20
40
60
80
100
120
140
.84
767-300ER / RB211-524HGround fuel mileage, nm/1000 kg
Altitude = 35,000 ft, Weight = 140,000 kg
Zero wind
G
r o u n d f u e l m
i l e a g e
60
80
100
120
140
160
180
200
220
240
.72 .73 .74 .75 .76 .77 .78 .79 .80 .81 .82
MACH number
737-800 / CFM56-7BGround fuel mileage, nm/1000 kg
Altitude = 35,000 ft, Weight = 68,000 kg
Zero wind
100 kt headwind100 kt headwind
200 kt headwind
200 kt headwind
100 kt tailwind100 kt tailwind
M R C
M R C
L R C
L R C
Examples of the effect of wind on ground fuel
mileage when flying near optimum altitude
Wind Effects On Cruise Mach Number
Zero wind LRCZero wind LRC
Descent
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87Fuel Conservation
Descent
• Penalty for early descent - spend more time at lowaltitudes, higher fuel burn
• Optimum top of descent point is affected by wind, ATC, speed restrictions, etc.
• Use information provided by FMC
• Use idle thrust (no part-power descents)
Descent
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88Fuel Conservation
Distance
Final cruisealtitude
Cost index
increasing
B
C I = 0 ( M
i n f u e l )
M i n t i m
e f r o
m p o i n t A
t o B
Descent
Cost Index = 0 minimizes fuel between a commoncruise point and a common end of descent point
Altitude
A
Approach
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89Fuel Conservation
pp
• Do not transition to the landing configurationtoo early
• Fuel flow in the landing configuration isapproximately 150% of the fuel flow in theclean configuration
Summary Of Operational Practices
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90Fuel Conservation
y p
• Minimize landing weight
• Do not carry more reserve fuel than required
• Use aft C.G. loading if possible
• Use lowest flap setting required
• Target optimum altitude (wind-corrected)
• Target LRC (or cost index)
• Choose most direct routing
• Use benefits of ETOPS routing
• Use tankering where appropriate
Flight Operations / Dispatchers
Summary Of Operational Practices
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91Fuel Conservation
Flight Crews
y p
• Minimize engine/APU use on ground
• Retract Flaps as early as possible• Fly the flight-planned speeds for all
phases of flight
• Use proper trim procedures
• Understand the airplane’s systems
• Understand wind/altitude trades• Don’t descend too early (or too late)
• Don’t transition to landing configuration
too early
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Maintenance Practices forFuel Conservation
Maintenance Personnel
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93Fuel Conservation
Opportunities For Fuel Conservation
• Airframe maintenance
• Engine maintenance
• Systems maintenance
Excess Drag Is Lost Payload
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94Fuel Conservation
g y
To Offset A 1% Increase In Drag,ZFW Would Need To Be Reduced
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95Fuel Conservation
717-200 ≈100 lb (45 kg)737-3/4/500 ≈120 lb (54 kg)
737-6/7/8/900 ≈130 lb (59 kg)
747-400 ≈
1,700 lb (771 kg)757-2/300 ≈260 lb (118 kg)
767-2/300 ≈600 lb (272 kg)
767-400 ≈
750 lb (340 kg)777-200 ≈1,000 lb (454 kg)
777-300 ≈1,100 lb (499 kg)
717-200 ≈ 1,000 lb (454 kg)737-3/4/500 ≈ 1,100 lb (499 kg)
737-6/7/8/900 ≈ 1,200 lb (544 kg)
747-400 ≈
5,800 lb (2,631 kg)757-2/300 ≈ 1,900 lb (862 kg)
767-2/300 ≈ 2,800 lb (1,270 kg)
767-400 ≈
3,200 lb (1,451 kg)777-200 ≈ 4,900 lb (2,222 kg)
777-300 ≈ 5,500 lb (2,495 kg)
Note: Reductions are approximate as actual values vary with distance flown.
ZFW reductions required tomaintain constant takeoff weight
ZFW reductions required tomaintain constant block fuel
Excess Drag Means Wasted FuelExcess Drag Means Wasted Fuel
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96Fuel Conservation
• 747 ≈ 100,000
• 777 ≈ 70,000
• 767 ≈ 30,000
• 757 ≈ 25,000
• 737 ≈ 15,000
• 727 ≈ 30,000
1% Drag In Terms Of Gallons Per Year
Total Drag Is Composed Of:
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97Fuel Conservation
Compressible drag ≈ drag due to Mach
• Shock waves, separated flow
Induced (vortex) drag ≈ drag due to lift
• Downwash behind wing, trim drag
Parasite drag ≈ drag not due to lift
• Shape of the body, skin friction, leakage,interference between components
• Parasite drag includes excrescence drag
Contributors To Total Airplane Drag
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98Fuel Conservation
Drag due toairplane sizeand weight
(unavoidable)~ 90%
Pressure, trim andinterference drag(optimized in the
wind tunnel)
~ 6%
Excrescence drag(this can increase)
~ 4%
(For a new airplane at cruise conditions)
What Is Excrescence Drag?
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99Fuel Conservation
The additional drag on the airplane due
to the sum of all deviations from asmooth sealed external surface
Proper maintenance can prevent anincrease in excrescence drag
Excrescence Drag On A ‘New Airplane’ Is Composed Of:
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100Fuel Conservation
0
1
2
3
4
Excrescence drag(% airplane drag)
Discrete items
Mismatchesand gaps
Internal airflow & sealleakage
Roughness &
surface irregularities
Total
Discrete Items
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101Fuel Conservation
• Antennas, masts, lights
• Drag is a function of design, size, position
Mismatched Surfaces
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102Fuel Conservation
Steps at skin joints, around windows, doors, controlsurfaces, and access panels
Frame
Skin
Internal Airflow
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103Fuel Conservation
Leaks through gaps,holes, and seals
AirflowAirflow
Roughness(Particularly Bad Near Static Sources)
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104Fuel Conservation
• Non-flush fasteners, rough surface
• Waviness, gaps
Non Flush Rivet Rough Surface
GapsWaviness
Most Important in Critical Areas
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105Fuel Conservation
Structural Repair Manuals Identify Critical Areas
747-400
Most Important in Critical Areas
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106Fuel Conservation
Some Models have ‘Extra Critical’ Areas Identified
737-800
Regular Maintenance Minimizes Deterioration
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107Fuel Conservation
• Flight control rigging
• Misalignments and mismatches• Aerodynamic seals
• Exterior surface finish
• OEW control
• Engine maintenance
• Instrument calibration
Flight Control Rigging
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108Fuel Conservation
Out of rig controls and flaps can cause a large
increase in fuel burn
747-400 examples:
• Aileron 1” out of rig ≈ 0.25% fuel
• Spoilers 1,2,3 and 4 up 2” ≈ 0.4% fuel
• Upper and lower rudder offset ≈ 0.35% fuel
• Inboard elevator 2” out of rig ≈ .4% fuel
In-Flight Inspections
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109Fuel Conservation
Several times during flight:
• Aileron and rudder trim ≈ 5 minutes
• Spoiler misfair ≈ 5 minutes
• Visual check of T.E. ≈ 10 minutes
(difficult to do during revenue service)
Misrigged Ailerons
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110Fuel Conservation
Misrigged outboard ailerons can resultin an increase in drag and fuel flow
Spoilers
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111Fuel Conservation
The spoilers begin to rise if the aircraft isbalanced by excessive autopilot lateral input
Control Surface Rigging Check
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112Fuel Conservation
747 example≈
includes fit and fair check:
• Ailerons ≈ 4 hours (1 - 2 people)
• Spoilers ≈ 2 hours (2 people)
• Flaps and Slats ≈ 3 hours (1 - 2 people)
• Rudders ≈ 3 hours (1 - 2 people)
• Elevators ≈ 2 hours (2 people)
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Surface Mismatch
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114Fuel Conservation
Surface Mismatch – ADF Antenna Fairing – negative step
Surface Mismatch
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115Fuel Conservation
Engine inlet secondary inlet door mismatch – positive step
Leading Edge Mismatch
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116Fuel Conservation
727 surface mismatch-R.H. Wing leading edge
slat actuator rod cover - positive stepAirflow
Check for Tight Aircraft Doors
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117Fuel Conservation
Note the tight and even fit of the airconditioning compartment access doors
Maintain Seals
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118Fuel Conservation
• Passenger and cargo door seals
• Damaged seals allow air to leak out
• Lose ‘thrust recovery’ from outflow valves• Disrupts flow along the fuselage
Passengerdoors
Fwd cargo
door sealdepressor
before repair
Check for Missing or Damaged Seals
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119Fuel Conservation
747 R.H. Wing gear well door forward
outboard seal missing and damagedAirflow
Check for Rough Surface Paint
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120Fuel Conservation
747 rough paint - lower fuselage
Airflow
Maintain a Clean Airplane
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121Fuel Conservation
• Maintain surface finish
• Fluid leaks contribute to drag
• Periodic washing of exterioris beneficial
– 0.1% drag reduction ifexcessively dirty
– Minimizes metal corrosionand paint damage
– Location of leaks and localdamage
• Customer aesthetics
Approximate Inspection Times for 747-size Aircraft
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122Fuel Conservation
• Seal inspections ≈ 1 hour
• Nacelles and struts ≈ 2 hours
• Wing/body/tail misfairs ≈ 2 hours
• General roughness and appearance ≈ 1 hour • Pressurized fuselage leak ≈ 2 hours
• Landing gear door check ≈ 1.5 hours
Average Results Of In-service Drag Inspections
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123Fuel Conservation
Average total airframe drag deterioration ~ 0.65%,
composed mainly of:• Control Surface Rigging ≈ 0.25%
• Deteriorated Seals ≈ 0.20%
• Misfairs ≈ 0.1%
• Roughness ≈ 0.05%
• Other ≈ 0.05%
Remember...
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124Fuel Conservation
• A well-maintained airplane should not exceed ≈ 0.5%drag increase over its new-airplane level
• Most inspections show less
747-400 Engine Swap Experiment
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125Fuel Conservation
• 747-400 engine swap experiment in 1996 supported themaximum drag increase for a well-maintained airplane
to be within approximately 0.5%• Engines from a 6-year old airplane with poor fuel mileage
were exchanged with those of a brand new airplane
• Fuel mileage levels were measured before and after theengine exchanges
• The unexplainable portion of the change in fuel mileage
for the same set of engines on an old and new airframewould be attributed to airframe effects only
747-400 Engine Swap Experiment
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126Fuel Conservation
• First, the old airplane went through a configurationinspection, followed by a D-check
• Control surfaces and seals were repaired, and one newengine was installed, but a known pneumatic systemleak was not fixed (worth ≅ 0.15% in fuel mileage)
• Fuel mileage data was collected both before and afterthe D-check
- 5
- 4
- 3
- 2
- 1
0
F u e l m i l e a g e d e v i a t i o n
F r o m d a t a b a s e
l e v e l ~ %
- 4.1%
- 3.4%
Pre
D-checkPost
D-check
F u e l m i l e a g e d
i f f e r e n c e ~ %
+2
+1
0
+ 0.7%+ 0.3% flightControls
+ 0.4% engineChange
Fuel mileagechange across
the D-check
747-400 Engine Swap Experiment
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127Fuel Conservation
• Fuel mileage data was collected on both the old
and new airplanes prior to the engine exchange,and following the exchange
• Results from all four sets of data were compared inorder to determine the airframe’s contribution to thedifferences in fuel mileage between the old and newairplanes
747-400 Engine Swap Experiment
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128Fuel Conservation
F
u e l m i l e a g e d e v i
a t i o n ~ %
- 4
- 3
- 2
- 1
0
1
2
3
F
u e l m i l e a g e d e v i a t i o n ~ %
- 4
- 3
- 2
- 1
0
1
2
3
+ 0.3%
- 0.6%
Newengines
Old airplane New airplane
Improved0.9%
F u e l m i l e a g e d e
v i a t i o n ~ %
- 4
- 3
- 2
- 1
0
1
2
3
- 3.4% F u e l m i l e a g e d e
v i a t i o n ~ %
- 4
- 3
- 2
- 1
0
1
2
3
- 2.6%
Oldengines
Old airplane New airplane
Improved
0.8%
747-400 Engine Swap Experiment
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129Fuel Conservation
0
.2
.4
.6
.8
1.0
1.2
D
i f f e r e n c e i n f u e l m i l e a g e ~ % Total
difference
0.85%
New verticalfin fairing
0.2%0.1%
0.55%
Pneumaticleakage
Actualdifference
due to drag
- - =
• Because the performance level of the old airplane whenit was first delivered is not known, it is not possible to
determine whether this actual difference is due to dragdeterioration, or just airplane to airplane variability
• For the same set of engines, the old airplane averaged.85% worse than the new airplane
• Is this all due to drag deterioration on the old airplane?
OEW Control
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130Fuel Conservation
• Operating empty weight (OEW) grows on average+ 0.1% to 0.2% per year, leveling off around 1%in 5 to 10 years
• Most OEW growth is mainly due to:
– Moisture
– Dirt
Engine Maintenance
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131Fuel Conservation
• Need to balance savings from performanceimprovements versus cost to perform maintenance
• Maintenance performed on high and low pressureturbines and compressors will help keep fuelconsumption from deteriorating
Items That Cause Engine/Fuel Burndeterioration
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132Fuel Conservation
Erosion / Wear / Contamination• Blade rubs - HP compressor, HP turbine, airfoil blade erosion
• Thermal distortion of blade parts
• Blade leading edge wear
• Excessive fan rubstrip wear
• Lining loss in the HP compressor
• Oil or dirt contamination of LP/HP compressor
Seals / Valves / Cooling
• Loss of High Pressure Turbine (HPT) outer air seal material
• Leaking thrust reverser seals
• ECS anomalies/leaks
• Failed-open fan air valves/Failed-open IDG air-oil coolervalves
• Faulty turbine case cooling/Faulty 11th stage cooling valves
Engine Components Are Affected By TheEnvironment In Which They Operate
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133Fuel Conservation
Typical Engine Deterioration Mechanisms
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134Fuel Conservation
Increased tip
clearances
Seal leakage
Airfoil
erosion
Dirt
accumulation
(Courtesy of Pratt & Whitney)
Scheduled Refurbishing Recovers SFC and EGT
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135Fuel Conservation (Courtesy of Pratt & Whitney)
SFCor
EGT
Hours or cycles
Shopvisit
Shopvisit
Regular shop visits recover SFC and EGT margin,but what can be done between these major visits?
Simple Procedures Can Recover PerformanceBetween Scheduled Shop Visits
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136Fuel Conservation
On-Wing Engine Washing
• Addresses dirt accumulation
On-Wing Engine Bleed Rigging
• Addresses leakage caused by bleedsystem wear
(Courtesy of Pratt & Whitney)
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Sample Impact of Water Wash Frequency
SFC and EGT Can Be Recovered Between ShopVisits Using Repetitive Engine Washes
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138Fuel Conservation
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 1000 2000 3000 4000 5000 6000
Cycles
% ∆TSFC
Unwashed
0.75%500 cycle washcumulative benefit
0.5%1000 cycle washcumulative benefit
Sample Impact of Water Wash Frequency
1000 cycle wash
500 cycle wash
(Courtesy of Pratt & Whitney)
On-Wing Water Wash: Costs versus Benefits
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139Fuel Conservation
Costs
• 6-8 man-hours per wash
• Waste water disposal
• Airplane ‘down’ time
Benefits (estimated annual per engine)
• Fuel savings of $20000 to $30000
• CO2 reduction of 190 to 290 tonnes
• Maintenance cost savings of $4000 to $6000
Note: Assumes 777-type airplane, 6.5 hr cycle, 620 cycles/yr., $1.00/gallon fuel).
(Courtesy of Pratt & Whitney)
On-Wing Engine Bleed RiggingRepair of Leaking Bleed Valves Saves Fuel
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140Fuel Conservation
• Simple procedure
• Start, stability, service bleeds
• Problem Identified from in-flightperformance trends
Up to 2.5% SFC benefit
(Courtesy of Pratt & Whitney)
p g
Instrument Calibration
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141Fuel Conservation
• Speed measuring equipment has a large impacton fuel mileage
• If speed is not accurate the airplane may be flyingfaster or slower than intended
• On the 747-400, flying 0.01M faster can increase
fuel burn by 1% or more
Airspeed System Error Penalty
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142Fuel Conservation
• Keep airspeed system maintained
• Airspeed reads 1% low, you fly 1% fast
• About 2% drag penalty in a 747
Check Static Sources
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143Fuel Conservation
Plugging or deforming the holes in the alternate static port can result
in erroneous instrument readings in the flight deck. Keeping thecircled area smooth and clean promotes aerodynamic efficiency.
Proper and Continuous Airframe and Engine MaintenanceWill Keep Your Airplanes Performing at Their Best!
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144Fuel Conservation
Don’t let this…Don’t let this…
Become this!Become this!
It Takes the Whole Team to Win
Conclusions
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145Fuel Conservation
• Large fuel savings results from the accumulationof many smaller fuel-saving actions and policies
• Dispatch, flight operations, flight crews, maintenance,management, and fuel contracts people all need tocontribute
• Program should be tailored to your airline’s specificrequirements and constraints
For More Information
Handout Of Boeing Articles Related To Fuel Conservation
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146Fuel Conservation
Sources:
• Airliner Magazine
– 1958 to 1997
• Newsletters (self-contained inserts in the Airliner Magazine)
– Fuel Conservation Newsletter - January 1981 toDecember 1983
– Fuel Conservation & Operations Newsletter - January 1984to June 1994
– Operations Newsletter - July 1994 to December 1997
• Aero Magazine (replaced Airliner after Boeing - MDC merger)
– January 1998 to 2003
Handout Of Boeing Articles Related To Fuel Conservation
For More Information
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147Fuel Conservation
• Airplane Maintenance For Fuel Conservation(sign-up sheets available in front of the classroom)
• DC-9, DC-10, and MD-11 specific fuel conservation
documents available upon request
• International Air Transportation Association website:
http://www.iata.org/whatwedo/fuel/fuelaction/fuel_conservation.htm
(Large amount of info here, including document “Guidance Materialand Best Practices for Fuel and Environmental Management”, datedDecember, 2004, which can be downloaded for free)
• ICAO Circular 303 “Operational opportunities to MinimizeFuel Use and Reduce Emissions”, published February,2004
– Can be ordered from ICAO website for $55 USD
http://www.icao.int
Questions?
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148Fuel Conservation
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End of Fuel Conservation
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