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Fuel Conservation
Flight Operations EngineeringBoeing Commercial Airplanes
November 2004
2Fuel Conservation
What is Fuel Conservation?
Fuel conservation means managing the operation and condition of an airplane to minimize the fuel used on every flight
3Fuel Conservation
*Assumes typical airplane utilization rates. Actual utilization rates may differ.
How Much Is A 1% Reduction In Fuel Worth?
Airplane Fuel savings*type gal/year/airplane
777 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
4Fuel Conservation
How Much Is This Worth In $$?
Depends on Current Fuel Prices!
5Fuel Conservation
Jet Fuel Prices
Source: Air Transport WorldYear
$/ga
llon
$0.00
$0.20
$0.40
$0.60
$0.80
$1.00
$1.20
$1.40
87 89 91 93 95 97 99 01 03
$1.00
6Fuel Conservation
Airplane Fuel savings* Fuel savings*type gal/year/airplane $/year/airplane
*Assumes $1.00/gallon
How Much Is A 1% Reduction In Fuel Worth?
777 70,000 →90,000 $70,000 → 90,000
767 30,000 →40,000 $30,000 → 40,000
757 25,000 →35,000 $25,000 → 35,000
747 100,000 →135,000 $100,000 → 135,000
737 15,000 →25,000 $15,000 → 25,000
727 30,000 →40,000 $30,000 → 40,000
*Assumes typical airplane utilization rates. Actual utilization rates may differ.
7Fuel Conservation
What Is Fuel Conservation From An Airline Business Viewpoint ?
Fuel conservation means managing the operation and condition of an airplane to minimize the fuel used on every flight
total cost oftotal cost of
8Fuel Conservation
Total savings =fuel savings
- cost to implement
Cost to Total CostImplement 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 $70,000 →90,000
767 30,000 →40,000 $30,000 →40,000
757 25,000 →35,000 $25,000 →35,000
747 100,000 →135,000 $100,000 →135,000
737 15,000 →25,000 $15,000 →25,000
727 30,000 →40,000 $30,000 →40,000
*Assumes $1.00/gallon*Assumes typical airplane utilization rates. Actual utilization rates may differ.
9Fuel Conservation
Saving Fuel Requires Everyone’s Help
• Flight Operations
• Dispatchers
• Flight Crews
• Maintenance
• Management
10
FLIGHTOPERATIONS
ENGINEERING
Operational Practices for Fuel Conservation
11Fuel Conservation
Flight Operations / Dispatchers
• Landing weight
• Fuel reserves
• Airplane loading
• Flap selection
• Altitude selection
• Speed selection
• Route selection
• Fuel tankering
Opportunities For Fuel Conservation
12Fuel Conservation
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)
13Fuel Conservation
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
14Fuel Conservation
Approximate % 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
15Fuel Conservation
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
16Fuel Conservation
Reducing Unnecessary Fuel Reduces Landing Weight
• Practice cruise performance monitoring
• Flight plan by tail numbers
17Fuel Conservation
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
18Fuel 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
19Fuel Conservation
Regulatory Requirements
• Is this an international flight?
• FAA rules?
• ICAO rules?
• Other rules?
20Fuel 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 the airport 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 alternate airport (or the destination airport if no alternate is required) under standard temperature conditions.
FAR 121.645(b)
DC
B
A
ContingencyContingency
AlternateAlternate
HoldingHolding
21Fuel Conservation
FAA “Island Reserves”
• No alternate is specified in release under Section 121.621(a)(2) or Section 121.623(b).
• Must have enough fuel, considering wind and other weather conditions expected, to fly to destination airport and thereafter to fly for 2 hours at normal cruising fuel consumption
FAR 121.645(c)
22Fuel 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 the flight plan; and then
B) To fly for 30 minutes at holding speed at 450 M (1,500 ft) above the alternate aerodrome under standard temperature conditions, and approach and land; and
C) To have an additional amount of fuel sufficient to provide for the increased consumption on the occurrence of any of the potential contingencies specified by the operator to the satisfaction of the state of the operator (typically a percentage of the trip fuel: 3% to 6%).
CA
B
ContingencyContingency
HoldingHoldingAlternateAlternate
ICAO Annex 6 (4.3.6.3)
23Fuel Conservation
Alternate Airport
What items should you consider when choosing an alternate airport?
• Airline facilities
• Size and surface of runway
• Weather
• Hours of operation, lighting
• Fire fighting, rescue equipment
24Fuel Conservation
Alternate Airport
What items should you consider when choosing an alternate airport?
• Airline facilities
• Size and surface of runway
• Weather
• Hours of operation, lighting
• Fire fighting, rescue equipment
25Fuel Conservation
Speed Selection for Holding
• Want to maximize time per kilogram of fuel
• Use published/FMC recommended holding speeds
26Fuel Conservation
Use Redispatch to Lower Contingency Fuel
• Reserve/contingency fuel is a function of trip length or trip fuel burn
• Originally implemented to cover errors in navigation, weather prediction, etc...
• Navigation and weather forecasting techniques have improved, decreasing the chance that contingency fuel will actually be used
27Fuel Conservation
How Redispatch Works
Climb
Descent
Cruise
Intended destination
Origin
Redispatchpoint
Initialdestination
28Fuel Conservation
Intendeddestination Origin
Intendeddestination Origin
Redispatchpoint
Initialdestination
Redispatchpoint
Initialdestination
Off Track Initial Destination
29Fuel Conservation
Intent is to lower the Contingency Fuel On Board at the Final Destination
Distance (Time)
Redispatchpoint
Contingencyfuel
Contingency Fuel required
Intended destination
Contingency
Fuel required
Red
uctio
n
30Fuel Conservation
Reduced fuel load
Increased payload
Benefits of Redispatch
31Fuel 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)
32Fuel Conservation
Example of payload increase with constant
takeoff weight
OEW
PAYLOAD(1)
Altern + HoldContingency
TRIPFUEL
TRIPFUEL
Same takeoff weight with and without redispatch
Optimum
redispatchpoint
A C
OEW
A B(No redispatch)
PAYLOAD(2)
Altern + HoldContingency
PAYLOAD(2)
B C
OEW
TRIP FUELAltern + Hold
ContingencyGross weight
33Fuel Conservation
Example of takeoff weight and landing
weight decreases with constant payload
OEW
PAYLOAD(1)
Altern + HoldContingency
TRIPFUEL
TRIPFUEL
Optimum
redispatchpoint
A C(No redispatch)
A B B C
OEW
PAYLOAD(2)
PAYLOAD(2)
OEW
TRIP FUEL
Altern + HoldContingency ContingencyAltern + Hold
Takeoff weight decrease
Landing weight (1)
Landing weight (2)
(decrease fro
m (1))
Gross weight
34Fuel 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 forward c.g. due to the smaller moment arm between Liftwing and WT
• Less angle of attack, α, is required to create the lower Liftwingrequired 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 LoadingMaintain C.G. In The Mid To Aft Range
35Fuel Conservation
3632282420161284
Center of gravity, %MAC
Incremental cruise drag, %
-2
-1
0
1
2
3
4
5
0.70
0.65
0.60
0.550.50
Typical trim drag increment at cruise Mach
Airplane Loading (continued)Maintain C.G. in the Mid to Aft Range
W/δ (LB *10-6)
Actual variation in drag due to C.G.
depends on airplane design, weight,
altitude and Mach
36Fuel Conservation
Flap Setting
Choose lowest flap setting that will meet takeoff performance requirements:
• Less drag
• Better climb performance
• Spend less time at low altitudes, burn less fuel
37Fuel Conservation
Altitude Selection
Pressure altitude for a given weight and speed schedule that produces the maximum air miles per unit of fuel
Optimum Altitude Definition
38Fuel Conservation
Definition of Optimum Altitude
FUEL MILEAGE (NAM/LB)
PRES
SUR
E A
LTIT
UD
E (1
000
FT)
0.024 0.028 0.032 0.036 0.040 0.044 0.04830
32
34
36
38
40
GROSS WT(1000 LB)
620
580
540
500
460 420 380 340300
OPTIMUM
(CONSTANT MACH NUMBER)
Pressure Altitude Which Provides the Maximum Fuel Mileage for a Given Weight and Speed
39Fuel Conservation
LRC Mach
Determining Optimum Altitude
Cruise weight (1000 KG)
Brake release weight (1000 KG)
45
40
35
30 70 60 90 80 110 100 120
70 80 90 100 100 120
Pressure altitude (1000 ft)
40Fuel Conservation
Step Climb
= Off optimum operations Optimum
Altitude
4000 ft
2000 ft
Stepclimb
41Fuel Conservation
Optimum altitude
+ 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 Penalty4000 ft Step vs. No Step Over a 4-Hour Cruise
(Example Only)
42Fuel Conservation
Speed Selection
NAM/pound fuel
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
Increasing weight
LRC
MMO
MRC = Maximum range cruise (speed producing maximum fuel mileage for a given weight)LRC = Long Range cruise (speed which produces a 1% decrease in FM relative to MRC)
1%
LRC Versus MRC
MRC
43Fuel Conservation
Speed Selection (continued)
• LRC = MRC + 1% fuel burn
• Significant speed increase for only a 1% decrease in fuel mileage
• Increases speed stability
• Minimizes throttle adjustments
LRC Versus MRC
44Fuel Conservation
0
1
2
3
4
5
6
7
8
0.00 0.01 0.02 0.03 0.04
∆ Mach from MRC
∆ Fu
el ~
%
-30
-25
-20
-15
-10
-5
00.00 0.01 0.02 0.03 0.04
∆ Mach from MRC
∆ Ti
me
~ m
in.
LRC
Model #1
Model #2
Model #2
Model #1
LRC
Mod
el #
1
LRC
Mod
el #
2
∆ Fuel For Flying Faster Than MRC
Flying Faster Than MRC?Flying faster than LRC typically produces a significant fuel
burn increase in return for a relatively small time savings(example based on 5000 NM cruise)
∆ Time For Flying Faster Than MRC
Actual fuel burn increase, and time decrease, for flying faster than MRC depends on specific airplane model, weight, and altitude
45Fuel 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 ~ $/hrFuel cost ~ cents/lb
46Fuel Conservation
Route Selection
Choose the most favorable route available!
47Fuel Conservation
Great Circle Distance
• Shortest ground distance between 2 points on the earth’s surface
• May not be the shortest time when winds are included
48Fuel Conservation
ETOPS
• ETOPS allows for more direct routes
• Shorter routes = less fuel required
New York
Montreal
St. Johns
Goose Bay
IqaluitKangerlussuaq
Reykjavik
Shannon Paris
120 min
60 min
3148
3461
Using 120 min ETOPS leads to a 9% savings in trip distance!
49Fuel Conservation
Fuel Tankering
Fuel tankering is the practice of carrying more fuel than required for a particular sector in order to reduce the quantity of fuel loaded at the destination airport for the following sector (or sectors)
What Is It?
50Fuel 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 1
Fuel 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)
51Fuel Conservation
Reduction in total fuel costs for multiple leg flights is usually the main reason for tankering
Reduction in total fuel costs for multiple leg flights 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?
52Fuel Conservation
Fuel Tankering (continued)
• If price at departure airport is sufficiently less than at the destination airport, surplus fuel could be carried from the 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 (often called ‘surplus fuel burn-off’)
• Surplus fuel burn-off must be accounted for in any price differential calculation
• To be cost-effective, the difference in fuel price between the departure and destination airports must be large enough to offset the cost of the additional fuel burned in carrying the tankered fuel
Fuel Price Differential
53Fuel 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 when loading extra fuel for tankering!
Limitations On Total Amounts
54Fuel 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 overweight landing could result
• Higher maintenance costs: engines, reversers, wheels, tires, brakes
Additional Considerations
55Fuel 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 the requirements of your operations. (e.g., If the decision to tanker is made by the captain at the time 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
56Fuel 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
57Fuel Conservation
Cost Calculations (continued)
• All methods should begin by checking whether takeoff and landing weight limits, along with fuel capacity limits, allow additional fuel to be loaded
• Some operators choose a minimum tankeringamount such that if the amount available to tanker is not at least equal to their chosen minimum, no fuel will be tankered
58Fuel Conservation
Cost Calculations (continued)
Calculation of fuel prices is not always as easy as 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 (affects
price per gallon - as more fuel is purchased, the hookup price/gallon decreases)
• Taxes charged may be returned later as tax rebates lower the price per gallon
59Fuel Conservation
‘Assumed Percentage Burn-off’ Method
• Assumes a fixed percentage of the tankered fuel is consumed per hour of flight time; usually 4 to 5% per hour
• Divide total cost of additional fuel purchased at departure airport by amount remaining at destination 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 the allowance for unknown costs
• If price of fuel at destination is above the breakeven price, then it is cost-effective to tanker
60Fuel 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
61Fuel Conservation
Trip distance (nm) Break-even price ratio
200400600800
100020003000400050006000
1.0121.0231.0341.0461.0611.1301.2171.3341.4951.722
Sample
data only
varie
s with
airp
lane m
odel
Sample
data only
varie
s with
airp
lane m
odel
• To economically justify tanker operation, the fuel price at the destination must be greater than the break-even fuel price
Break-Even Price Ratio Method
• Method used in Boeing FPPM (found in chapter 2 text)• Break-even price ratio is presented as a function of trip
distance only
62Fuel Conservation
$ * (tankered fuel) = $ * (tankered fuel - fuel burnoff)gal gal
Orig Dest = tankered fuelremaining at dest
Break-evenprice ratioOrig
$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 the cost of purchasing the fuel at the destination is equivalent to the cost of purchasing the same amount of fuel, plus the fuel required to carry it, at the origin
• Break-even price occurs when:
63Fuel 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 any allowance for additional maintenance costs; it only considers the extra fuel burn off
64Fuel Conservation
Example Cost Calculation
Fuel price at origin: $0.80/galModel: 737-700/CFM56-7B24
Trip distance: 2000 NM
Trip distance, nm Break-even price ratio200400600800
1000200030004000
1.0151.0311.0451.0591.0751.1751.3111.477
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)
65Fuel 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 not tankering fuel
• Requires calculation of fuel required for actual routes with and without tankering
66Fuel Conservation
A B C
Leg 1 Leg 2
galA
$ Fuelreq’dleg 1
Fuelcarriedfor usein leg 2
+Extra fuelburned on
leg 1 due toextra wt
+ +Additional
incrementalcosts due tohigher weight gal
B
$+
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)
67Fuel Conservation
cost of tankering the fuel cost of purchasingat the destination
galB
$fuelcarriedfor usein leg 2
+extra fuelburned on
leg 1 due toextra weight
+additional
incrementalcosts due tohigher weight
- *gal
A
$fuel
carriedfor usein leg 2
‘Relative Cost to Tanker’ Method (continued)
Relative cost to tanker =
68Fuel 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 below which there will not be tankering. (e.g., if minimum gain selected as $100, then tankering will only be used if relative cost to tanker < - $100)
• Multiple legs (3 or more) add significantly to the complexity of the analysis
‘Relative Cost to Tanker’ Method (continued)
69Fuel Conservation
Additional Applications
• If fuel is tankered in order to obtain a shorter turnaround time at a given destination you can determine the relative 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)
70Fuel Conservation
Fuel Tankering
• Most flight planning services offer tankeringanalyses to their customers
• You can work with your flight planning service on which assumptions to use/include, and in what form the results should be reported
71Fuel Conservation
Flight Crew
Opportunities for Fuel Conservation:• Practice fuel economy in each phase of flight• Understand the airplane’s systems - Systems
Management
72Fuel Conservation
Engine Start
• Start engines as late as possible, coordinate with ATC departure schedule
• Take delays at the gate if possible
• Minimize APU use if ground power available
73Fuel Conservation
Taxi
• Take shortest route possible
• Use minimum thrust and minimum braking
• Taxi with all engines operating?
74Fuel 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:
75Fuel 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
* Assumes all engines operating during taxi
76Fuel Conservation
Takeoff
• Retract flaps as early as possible
• Full rate or derate to save fuel?
(Use of full rate will save fuel for a given takeoff, but general consensus is that in the long-term, total costs will be reduced by using reduced takeoff thrust)
77Fuel 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)
∆TS
FC @
100
0 cy
cles
Estimated Reduced ThrustImpact at 1000 Cycles
15% Average Thrust Reduction Can Improve Overall TSFC at 1000 Cycles by over 0.4%
(Courtesy of Pratt & Whitney)
Reduced Take Off ThrustImproves Long-term Performance Retention
78Fuel Conservation
Distance
Altitude
Initial cruise altitude
Cost indexincreasing
A
BCI
= 0
(M
in fu
el)
Min time to Point B
Max
gra
dien
t
Climb
Cost Index = 0 minimizes fuel to climb and cruise to a common point in space
79Fuel Conservation
Cruise
• A plane flying in steady, level flight may require some control surface inputs to maintain lateral-directional control
• Use of the proper trim procedure minimizes drag
• Poor trim procedure can result in a 0.5% cruise drag penalty on a 747
• Follow the procedures provided in the Flight Crew Training Manual
Lateral - Directional Trim Procedure
80Fuel Conservation
Systems ManagementCruise
• 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
81Fuel Conservation
WindsCruise
• Wind may be a reason to choose an “off optimum” altitude
• Want to maximize ground miles per unit of fuel burned
• Wind-Altitude trade tables are provided in the flight crew operations manual
82Fuel Conservation
Fuel Mileage = =Fuel Flow
VTAS
KGNAM
Fuel Used = =NGM/KG
NGM
NAM/KG
NAM=
VTAS + VWIND
(NGM) (Fuel Flow)
Ground Fuel Mileage = =Fuel Flow
VTAS + VWIND
KGNGM
In cruise: positive wind = Tailwindnegative wind = Headwind
VGround
Wind Effects On Fuel Mileage
83Fuel Conservation
Typical Wind/Altitude Trade Table
Wind Effects On Cruise Altitude: Wind/Alt Trade
33 knots greater tailwind (or, lower headwind) would be
required at FL310 relative to FL350 to obtain equivalent
ground fuel mileage
84Fuel Conservation
MACH number
Gro
und
fuel
mile
age
.80 .81 .82 .83 .84 .85 .8664
66
68
70
72
74
76
78
35K, Wind = 0
31K, Wind = 0
MACH number
Gro
und
fuel
mile
age
.80 .81 .82 .83 .84 .85 .8664
66
68
70
72
74
76
78
35K, Wind = 0
31K, Wind = 0
Wind = 10
Wind = 20
Wind = 30
Wind = 40
LRC, 35K
Typical Wind Altitude/Trade for Constant Airplane Weight
Example of increasing Tailwind at 31,000 ft Example of increasing headwind at 35,000 ft
LRC, 31K
LRC, 31K
LRC, 35K
Wind = -10
Wind = -20
Wind = -30
Wind = -40
Wind Effects On Cruise Altitude: Wind/Alt Trade
* Actual ground fuel mileage comparisons vary with airplane model, weight, and altitudes considered
85Fuel Conservation
Gro
und
fuel
mile
age
60
80
100
120
140
160
180
200
220
240
.72 .73 .74 .75 .76 .77 .78 .79 .80 .81 .82
MACH number
Zero wind
100 kt headwind
200 kt headwind
100 kt tailwind
MRC
LRC
Typical affect of wind on ground fuel mileage when flying a constant altitude and weight
Wind Effects On Cruise Mach Number
Zero wind LRC
* Actual ground fuel mileage comparisons vary with airplane model, weight, and altitudes considered
86Fuel Conservation
Descent
• Penalty for early descent - spend more time at low altitudes, 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)
87Fuel Conservation
Distance
Final cruise altitude
Cost indexincreasing
B
CI = 0 (Min fuel)
Min tim
e from point A to B
Descent
Cost Index = 0 minimizes fuel between a common cruise point and a common end of descent point
Altitude
A
88Fuel Conservation
Approach
• Do not transition to the landing configuration too early
• Fuel flow in the landing configuration is approximately 150% of the fuel flow in the clean configuration
89Fuel Conservation
Summary Of Operational Practices
• 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
90Fuel Conservation
Flight CrewsSummary Of Operational Practices
• 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
Maintenance Practices for Fuel Conservation
92Fuel Conservation
Opportunities For Fuel ConservationMaintenance Personnel
• Airframe maintenance
• Engine maintenance
• Systems maintenance
93Fuel Conservation
Excess Drag Is Lost Payload
94Fuel Conservation
Excess Drag Means Wasted FuelExcess Drag Means Wasted Fuel
• 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
* Assumes typical airplane utilization rates. Actual utilization rates may differ.
95Fuel Conservation
Total Drag Is Composed Of:
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
96Fuel Conservation
Drag due to airplane size and weight (unavoidable)
~ 90%
Pressure, trim and interference drag (optimized in the wind tunnel)
~ 6%
Excrescence drag (this can increase)
~ 4%
Contributors To Total Airplane Drag(New Airplane at Cruise Conditions)
* Typical values for illustration purposes. Actual magnitudes vary with airplane model
97Fuel Conservation
What Is Excrescence Drag?
The additional drag on the airplane due to the sum of all deviations from asmooth sealed external surface
Proper maintenance can prevent an increase in excrescence drag
98Fuel Conservation
0
1
2
3
4
Excrescence drag(% airplane drag)
Discrete items
Mismatches and gaps
Internal airflow & seal leakage
Roughness & surface irregularities
Excrescence Drag On A ‘New Airplane’ Is Composed Of:
Total
* Typical values for illustration purposes. Actual magnitudes vary with airplane model
99Fuel Conservation
Discrete Items
• Antennas, masts, lights
• Drag is a function of design, size, position
100Fuel Conservation
Mismatched Surfaces
Steps and gaps at skin joints, around windows, doors, control surfaces, and access panels
Frame
Skin
101Fuel Conservation
Internal Airflow
Leaks from higher to lower pressure areas due to
deteriorated or poorly-installed aerodynamic seals
AirflowAirflow
102Fuel Conservation
Roughness (Particularly Bad Near Static Sources)
• Non-flush fasteners, rough surface
• Waviness, gaps
Non Flush Rivet Rough Surface
GapsWaviness
103Fuel Conservation
Most Important in Critical Areas
• Forward portion of fuselage and nacelle
• Leading areas of wings and tail
• Local Coefficient of Pressure (Cp) is highest
All spoilers up3.75” = 2% drag
Outboard aileron up4” = 1% drag
Rudder deflection 4.5 degrees(offset 9.5” at base) =2% drag
1” tall ridge on wing75 ft. long = 2% drag
747 Cruise Drag Sensitivities747 Cruise Drag Sensitivities
104Fuel Conservation
Regular Maintenance Minimizes Deterioration
• Flight control rigging
• Misalignments and mismatches
• Aerodynamic seals
• Exterior surface finish
• OEW control
• Engine maintenance
• Instrument calibration
105Fuel Conservation
Flight Control Rigging
Out of rig controls and flaps can cause a largeincrease 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
106Fuel Conservation
In-Flight Inspections Can be Easily Made
Several times during flight:
• Note required aileron and rudder trim ≈ 5 minutes• Visual check of spoiler misfair ≈ 5 minutes• Visual check of trailing edge of wing ≈ 10 minutes
107Fuel Conservation
Misrigged Ailerons
Misrigged outboard ailerons can result in an increase in drag and fuel flow
108Fuel Conservation
Spoilers
The spoilers can begin to rise if the aircraft is balanced by excessive autopilot lateral input
109Fuel Conservation
Control Surface Rigging Check
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)
110Fuel Conservation
Misalignment, Mismatch
Check items which are adjustable and could become misaligned after years of service:
• Adjustable panels• Landing gear doors• Entry doors and cargo doors
111Fuel Conservation
Surface Mismatch
Surface Mismatch – ADF Antenna Fairing – negative step
112Fuel Conservation
Surface Mismatch
Engine inlet secondary inlet door mismatch – positive step
113Fuel Conservation
Leading Edge Mismatch
727 surface mismatch-R.H. Wing leading edge slat actuator rod cover - positive step
Airflow
114Fuel Conservation
Positive Step and Improper Seal
727 surface mismatch - lower wing critical area(flap track fairing - fabricated leather seal) - positive step
Airflow
115Fuel Conservation
Check for Tight Aircraft Doors
Note the tight and even fit of the air conditioning compartment access doors
116Fuel Conservation
Maintain Seals
• Passenger and cargo door seals
• Damaged seals allow air to leak out
• Lose ‘thrust recovery’ from outflow valves
• Disrupts flow along the fuselage
Passenger doors
Fwd cargo door seal depressor
before repair
117Fuel Conservation
Check for Missing or Damaged Seals
747 R.H. Wing gear well door forward outboard seal missing and damaged
Airflow
118Fuel Conservation
Check for Rough Surface Paint
747 rough paint - lower fuselage
Airflow
119Fuel Conservation
Maintain a Clean Airplane
• Maintain surface finish
• Fluid leaks contribute to drag
• Periodic washing of exterior is beneficial– 0.1% drag reduction if
excessively dirty– Minimizes metal corrosion
and paint damage– Location of leaks and local
damage
• Customer aesthetics
120Fuel Conservation
Make Simple Inspections
• 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
121Fuel Conservation
Average Results Of In-service Drag Inspections
• Results of in-service airframe drag inspections show the most common contributors to airframe deterioration are:
– Control surface miss-rigging– Aerodynamic seal deterioration
• Lesser contributors include:– Skin surface miss-matches– Surface roughness– ‘Other’
122Fuel Conservation
OEW Control
• Operating empty weight (OEW) typically increases 0.1% to 0.2% per year, leveling off around +1% from a new-airplane level in 5 to 10 years
• Most OEW growth is mainly due to accumulation of:– Moisture– Dirt
123Fuel Conservation
Engine Maintenance
• Need to balance savings from performance improvements versus cost to perform maintenance
• Maintenance performed on high and low pressure turbines and compressors will help keep fuel consumption from deteriorating
124Fuel Conservation
Items That Cause Engine/Fuel Burn deterioration
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 cooler
valves • Faulty turbine case cooling/Faulty 11th stage cooling valves
125Fuel Conservation
Engine Components Are Affected By The Environment In Which They Operate
126Fuel Conservation
Typical Engine Deterioration Mechanisms
Increased tip clearances
Seal leakage
Airfoil erosion
Dirt accumulation
(Courtesy of Pratt & Whitney)
127Fuel Conservation
Scheduled Refurbishing Recovers SFC and EGT
(Courtesy of Pratt & Whitney)
SFC or
EGT
Hours or cycles
Shop visit
Shop visit
128Fuel Conservation
Simple Procedures Can Recover Performance Between Scheduled Shop Visits
On-Wing Engine Washing• Addresses dirt accumulation
On-Wing Engine Bleed Rigging• Addresses leakage caused by bleed
system wear
(Courtesy of Pratt & Whitney)
129Fuel Conservation
On-Wing Engine Washing
• Simple procedure• Special tooling identified• 3-4 hours, two mechanics
Up to 1.5% SFC improvements
possible
Hand wash fan and LPC stator vanes
Regular Intervals Ensure Fuel Economy
(Courtesy of Pratt & Whitney)
130Fuel 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 6000Cycles
% ∆TSFC
1000 cycle wash
Unwashed
500 cycle wash
0.5%1000 cycle washcumulative benefit
0.75%500 cycle washcumulative benefit
Example of Water Wash Frequency Impact
SFC and EGT Can Be Recovered Between Shop Visits Using Repetitive Engine Washes
(Courtesy of Pratt & Whitney)
131Fuel Conservation
On-Wing Engine Bleed Rigging
• Simple procedure
• Start, stability, service bleeds
• Problem Identified from in-flight performance trends
Up to 2.5% SFC benefit possible
Repair of Leaking Bleed Valves Saves Fuel
(Courtesy of Pratt & Whitney)
132Fuel Conservation
Instrument Calibration
• Speed measuring equipment has a large impact on fuel mileage
• If speed is not accurate the airplane may be flying faster or slower than intended
• On the 747-400, flying 0.01M faster can increase fuel burn by 1% or more
133Fuel Conservation
Airspeed System Error Penalty
• Keep airspeed system calibrated
• Airspeed reads 1% low, airplane flies 1% fast
• About 2% drag penalty in a 747
134Fuel 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.
Check Static Sources
135Fuel Conservation
Don’t let this… Don’t let this…
Become this!Become this!
Proper and Continuous Airframe and Engine Maintenance Will Keep Your Airplanes Performing at Their Best!
136Fuel Conservation
It Takes the Whole Team to WinConclusions
• Large fuel savings results from the accumulation of many smaller fuel-saving actions and policies
• Dispatch, flight operations, flight crews, maintenance, and management all need to contribute
• Program should be tailored to your airline’s needs and requirements
137Fuel Conservation
For More Information
• Airliner Magazine– 1958 to 1997
• Newsletters (self-contained inserts in the Airliner Magazine)– Fuel Conservation Newsletter - January 1981 to
December 1983– Fuel Conservation & Operations Newsletter - January 1984
to June 1994– Operations Newsletter - July 1994 to December 1997
• Aero Magazine (replaced Airliner after Boeing - MDC merger)– January 1998 to 2003
Boeing has published numerous articles addressing fuel conservation over the last 4 decades in the following publications:
End ofFuel Conservation
Flight Operations EngineeringBoeing Commercial Airplanes
November 2004