Fuel Conservation
Flight Operations Engineering
Boeing Commercial Airplanes
November 2004
What is Fuel Conservation?
Fuel conservation means managing the
operation and condition of an airplane to
minimize the fuel used on every flight
Fuel Conservation
2
How Much Is A 1% Reduction In Fuel Worth?
Airplane
type
Fuel savings*
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
*Assumes typical airplane utilization rates. Actual utilization rates may differ.
Fuel Conservation
3
How Much Is This Worth In $$?
Depends on Current Fuel Prices!
Fuel Conservation
4
Jet Fuel Prices
$1.40
$1.20
$1.00
$/gallon
$1.00
$0.80
$0.60
$0.40
$0.20
$0.00
87
89
91
93
95
97
99
01
03
Year
Source: Air Transport World
Fuel Conservation
5
How Much Is A 1% Reduction In Fuel Worth?
Airplane
type
Fuel savings*
gal/year/airplane
Fuel savings*
$/year/airplane
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.
Fuel Conservation
6
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 of
Fuel Conservation
7
How Much Is A 1% Reduction In Fuel Worth?
Airplane
Fuel savings*
type
gal/year/airplane
Fuel savings*
$/year/airplane
Cost to
Implement
Total Cost
Savings/AP
??
??
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
Total savings =
fuel savings
- cost to
implement
*Assumes $1.00/gallon
*Assumes typical airplane utilization rates. Actual utilization rates may differ.
Fuel Conservation
8
Saving Fuel Requires Everyone’s Help
• Flight Operations
• Dispatchers
• Flight Crews
• Maintenance
• Management
Fuel Conservation
9
FLIGHT
OPERATIONS
ENGINEERING
Operational Practices
for Fuel Conservation
10
Flight Operations / Dispatchers
Opportunities For Fuel Conservation
• Landing weight
• Fuel reserves
• Airplane loading
• Flap selection
• Altitude selection
• Speed selection
• Route selection
• Fuel tankering
Fuel Conservation
11
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)
Fuel Conservation
12
Components Of Landing Weight
Fuel on board at landing
WLDG
Required
= OEW + Payload + reserve +
fuel
Additional
fuel loaded
but not used
Zero fuel weight
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13
Reducing ZFW Reduces Landing Weight
Approximate % Block Fuel Savings Per
1000 Lb (454 Kg) ZFW Reduction
717-200
.9%
Fuel Conservation
7377377573/4/500 6/7/8/900 200/300
.7%
.6%
.5%
7672/3/400
777200/300
747-400
.3%
.2%
.2%
14
Reducing OEW Reduces Landing Weight
Items To Consider
• Passenger service items
• Passenger entertainment items
• Empty Cargo and baggage containers
• Unneeded Emergency equipment
• Excess Potable water
Fuel Conservation
15
Reducing Unnecessary Fuel
Reduces Landing Weight
• Practice cruise performance monitoring
• Flight plan by tail numbers
Fuel Conservation
16
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
Fuel Conservation
17
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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Regulatory Requirements
• Is this an international flight?
• FAA rules?
• ICAO rules?
• Other rules?
Fuel Conservation
19
FAA “International Reserves”
FAR 121.645(b)
A
B
C
D
(A) To fly to and land at the airport to which it is released;
Contingency
(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;
Alternate
(C) After that, to fly to and land at the most distant alternate airport specified in the
flight release, if an alternate is required; and
Holding
(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.
Fuel Conservation
20
FAA “Island Reserves”
FAR 121.645(c)
• 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
Fuel Conservation
21
ICAO International
ICAO Annex 6 (4.3.6.3)
C
A
B
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:
Alternate
Holding
Contingency
Fuel Conservation
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%).
22
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
Fuel Conservation
23
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
Fuel Conservation
24
Speed Selection for Holding
• Want to maximize time per kilogram of fuel
• Use published/FMC recommended holding
speeds
Fuel Conservation
25
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
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26
How Redispatch Works
Cruise
Redispatch
point
Climb
Descent
Origin
Fuel Conservation
Initial
destination
Intended
destination
27
Off Track Initial Destination
Origin
Initial
destination
Initial
destination
Intended
destination
Redispatch
point
Intended
destination
Origin
Redispatch
point
Fuel Conservation
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Intent is to lower the Contingency Fuel On
Board at the Final Destination
Intended
destination
Contingency
fuel
ting
n
o
C
F
y
c
n
e
u
ired
u
q
el re
ncy
e
g
n
ti
Con required
l
Fue
Reduction
Redispatch
point
Distance
(Time)
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Benefits of Redispatch
Increased payload
Reduced fuel load
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30
Examples of Using Redispatch
To: 1) Increase payload
2) Decrease takeoff and landing weight
(by reducing fuel load)
A
B
C
Origin
Initial
destination
Final
destination
Fuel Conservation
31
Same takeoff weight with and
without redispatch
TRIP
FUEL
Gross
weight
TRIP
FUEL
Contingency
Altern + Hold
Contingency
Altern + Hold
um oint
m
p
ti
Op atch
isp
red
TRIP FUEL
Altern + Hold
PAYLOAD
(1)
PAYLOAD
(2)
PAYLOAD
(2)
OEW
OEW
OEW
A
Fuel Conservation
Example of payload
increase with constant
takeoff weight
C
(No redispatch)
A
B
B
Contingency
C
32
Takeoff weight decrease
TRIP
FUEL
TRIP
FUEL
Gross
weight
Landing
weight (1)
int
o
m p
mu atch
i
t
Op disp
re
TRIP FUEL
Contingency
Altern + Hold
Contingency
Altern + Hold
Altern + Hold
PAYLOAD
(1)
PAYLOAD
(2)
PAYLOAD
(2)
OEW
OEW
OEW
A
Fuel Conservation
Example of takeoff
weight and landing
weight decreases with
constant payload
C
(No redispatch)
A
B
B
(2) )
t
igh (1)
e
w rom
g
f
n
di ase
n
La cre
(de
Contingency
C
33
Airplane Loading
Maintain C.G. In The Mid To Aft Range
Lift wing (aft c.g.) < Lift wing (fwd c.g.)
WT (fwd c.g.) = WT (aft c.g.)
Lift tail (aft c.g.)
Is less negative than
Lift tail (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 Liftwing
required to offset the WT plus the less negative Lifttail
• Same Lifttotal, but lower Liftwing and therefore lower α required
Fuel Conservation
34
Airplane Loading (continued)
Maintain C.G. in the Mid to Aft Range
Typical trim drag increment at cruise Mach
5
4
W/δ (LB *10-6)
0.70
3
Actual variation in
drag due to C.G.
depends on airplane
design, weight,
altitude and Mach
0.65
Incremental
cruise drag, %
0.60
2
0.55
0.50
1
0
-1
-2
4
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8
12
16
20
24
28
Center of gravity, %MAC
32
36
35
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
Fuel Conservation
36
Altitude Selection
Optimum Altitude Definition
Pressure altitude for a given weight and speed
schedule that produces the maximum air miles per
unit of fuel
Fuel Conservation
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Definition of Optimum Altitude
Pressure Altitude Which Provides the Maximum Fuel
Mileage for a Given Weight and Speed
PRESSURE ALTITUDE (1000 FT)
40
GROSS WT
(1000 LB)
38
460
580
380
340
300
500
540
36
420
O
IM
T
P
UM
34
620
(CONSTANT MACH
NUMBER)
32
30
0.024
0.028
0.032
0.036
0.040
0.044
0.048
FUEL MILEAGE (NAM/LB)
Fuel Conservation
38
Determining Optimum Altitude
45
Pressure
altitude
(1000 ft)
40
LRC Mach
35
30
60
70
80
90
100
110
120
Cruise weight (1000 KG)
70
80
90
100
100
120
Brake release weight (1000 KG)
Fuel Conservation
39
Step Climb
Step
climb
4000 ft
2000 ft
Optimum
Altitude
Fuel Conservation
= Off optimum operations
40
Off-Optimum Fuel Burn Penalty
4000 ft Step vs. No Step Over a 4-Hour Cruise
(Example Only)
+ 1.5%
+ 0.5%
+ 0%
+ 0.5%
+ 1.5%
4-hour Average = + 0.6%
t
Op
de
u
t
lti
a
m
u
m
i
1000 ft
4-hour Average = + 4.8%
+ 1.5%
Fuel Conservation
+ 3.0%
+ 4.5%
+ 6.5%
+ 8.5%
41
Speed Selection
LRC Versus MRC
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)
MRC
0.12
1%
LRC
0.11
MMO
0.10
NAM/
pound
fuel
0.09
Increasing
weight
0.08
0.07
0.06
0.05
0.60
0.64
0.68
0.72
0.76
0.80
0.84
MACH number
Fuel Conservation
42
Speed Selection (continued)
LRC Versus MRC
• LRC = MRC + 1% fuel burn
• Significant speed increase for only
a 1% decrease in fuel mileage
• Increases speed stability
• Minimizes throttle adjustments
Fuel Conservation
43
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)
∆ Fuel For Flying Faster Than MRC
-30
8
Model #2
Model #1
5
4
3
-20
-15
-10
2
1
-5
LRC
0
0
0.00
0.01
0.02
∆ Mach from MRC
0.03
0.04
0.00
0.01
LRC Model #2
∆ Fuel ~ %
Model #2
Model #1
LRC Model #1
6
-25
∆ Time ~ min.
7
∆ Time For Flying Faster Than MRC
0.02
0.03
0.04
∆ Mach from MRC
Actual fuel burn increase, and time decrease, for flying faster than
MRC depends on specific airplane model, weight, and altitude
Fuel Conservation
44
Speed Selection - Other Options
• Cost Index = 0 (maximize ngm/lb
= wind-adjusted MRC)
• Selected Cost Index (minimize costs)
Time cost ~ $/hr
CI =
Fuel cost ~ cents/lb
• Maximum Endurance (maximize time/lb)
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Route Selection
Choose the most favorable route available!
Fuel Conservation
46
Great Circle Distance
• Shortest ground distance between 2 points on the
earth’s surface
• May not be the shortest time when winds are
included
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47
ETOPS
• ETOPS allows for more direct routes
• Shorter routes = less fuel required
12
60
Iqaluit
Kangerlussuaq
0
m
in
m
in
Reykjavik
346
1
Shannon
Paris
Goose Bay
3148
Montreal
St. Johns
New York
Using 120 min ETOPS leads to
a 9% savings in trip distance!
Fuel Conservation
48
Fuel Tankering
What Is It?
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)
Fuel Conservation
49
Fuel Tankering (continued)
Leg 1
Leg 2
100% tankering
of 2nd leg fuel
Reserves
A
B
C
No tankering
of 2nd leg fuel
Extra fuel burned
on leg 1 to carry
fuel for leg 2
Reserves
Fuel loaded at
A for leg 1
Fuel Conservation
Fuel
for
leg 1
Fuel
for
leg 2
Fuel loaded at
B for leg 2
Fuel
for
leg 2
Fuel
for
leg 1
Fuel loaded
at A for legs 1 & 2
50
Fuel Tankering (continued)
Why Tanker Fuel?
• Shorter turnaround time
• Limited amount of fuel available
• Unreliable airport services
• Fuel quality at destination airport
• Fuel price differential
Reduction in total fuel costs for multiple leg
flights is usually the main reason for tankering
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51
Fuel Tankering (continued)
Fuel Price Differential
• 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 tankered
such 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 Conservation
52
Fuel Tankering (continued)
Limitations On Total Amounts
• 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!
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53
Fuel Tankering (continued)
Additional Considerations
• 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
Difficult to quantify, but should be
addressed in all cost calculations
Fuel Conservation
54
To Tanker or Not to Tanker
Cost Calculations
• 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
Fuel Conservation
55
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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56
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 tankering
amount such that if the amount available to tanker
is not at least equal to their chosen minimum,
no fuel will be tankered
Fuel Conservation
57
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
Fuel Conservation
58
‘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
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59
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
Fuel Conservation
60
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
Break-even price ratio
200
400
600
800
1000
2000
3000
4000
5000
6000
1.012
1.023
1.034
1.046
1.061
1.130
1.217
1.334
1.495
1.722
va
rie Sa
s mp
w l
ith e d
air ata
pl o
an n
e ly
m
od
el
Trip distance (nm)
• To economically justify tanker operation, the fuel
price at the destination must be greater than the
break-even fuel price
Fuel Conservation
61
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:
$ * (tankered fuel) = $ * (tankered fuel - fuel burnoff)
gal
gal Orig
Dest
$
Break-even price =
gal
at destination
Fuel Conservation
Dest
B.E.
=
= tankered fuel
remaining at dest
$
gal
Break-even
*
price ratio
Orig
62
Break-Even Price Ratio Method (continued)
• If the destination fuel price is greater than the breakeven 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
Fuel Conservation
63
Example Cost Calculation
Model: 737-700/CFM56-7B24
Trip distance: 2000 NM
Fuel price at origin: $0.80/gal
Trip distance, nm
Break-even price ratio
200
400
600
800
1000
2000
3000
4000
1.015
1.031
1.045
1.059
1.075
1.175
1.311
1.477
Break-even price = $0.80 ( 1.175) = $0.94
If dest. fuel price > $0.94, then more economical to tanker the fuel
If 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)
Fuel Conservation
64
‘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
Fuel Conservation
65
‘Relative Cost to Tanker’ Method (continued)
Leg 1
Leg 2
A
B
C
total cost with tankering
$
gal
A
Extra fuel
Fuel
Fuel
req’d + carried + burned on
leg 1 due to
for use
leg 1
extra wt
in leg 2
-
$
gal
*
A
Fuel
req’d
leg 1
-
Additional
incremental
+ costs due to +
higher weight
$
gal
*
B
$
gal
*
B
Additional
fuel req’d
for leg 2
Fuel
req’d
leg 2
Total cost with no tankering
Fuel Conservation
66
‘Relative Cost to Tanker’ Method (continued)
Relative cost to tanker =
$
gal
A
fuel
extra fuel
carried + burned on
for use
leg 1 due to
in leg 2
extra weight
additional
incremental
+ costs due to
higher weight
cost of tankering the fuel
Fuel Conservation
-
$
gal
*
B
fuel
carried
for use
in leg 2
cost of purchasing
at the destination
67
‘Relative Cost to Tanker’ Method (continued)
• If relative cost to tanker = 0, then breakeven
• If relative cost to tanker > 0, then costs are increased
by tankering
• If relative cost to tanker < 0, then costs are reduced
by 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
Fuel Conservation
68
‘Relative Cost to Tanker’ Method (continued)
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
Fuel Conservation
69
Fuel Tankering
• Most flight planning services offer tankering
analyses 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
Fuel Conservation
70
Flight Crew
Opportunities for Fuel Conservation:
• Practice fuel economy in each phase of flight
• Understand the airplane’s systems - Systems
Management
Fuel Conservation
71
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
Fuel Conservation
72
Taxi
• Take shortest route possible
• Use minimum thrust and minimum braking
• Taxi with all engines operating?
Fuel Conservation
73
Taxi
One Engine Shut Down Considerations:
• 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
Fuel Conservation
74
Sample Taxi and APU Fuel Burns
Condition
717
727
737
747
757
767
777
Taxi*
(lb/min)
25
60
25
100
40
50
60
APU
(lb/min)
4
5
4
11
4
4
9
* Assumes all engines operating during taxi
Fuel Conservation
75
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)
Fuel Conservation
76
Reduced Take Off Thrust
Improves Long-term Performance Retention
15% Average Thrust Reduction Can Improve
Overall TSFC at 1000 Cycles by over 0.4%
0.0%
∆ TSFC @ 1000 cycles
-0.1%
Estimated Reduced Thrust
Impact at 1000 Cycles
-0.2%
-0.3%
-0.4%
-0.5%
-0.6%
-0.7%
-0.8%
-0.9%
-1.0%
-25%
(Courtesy of Pratt & Whitney)
Fuel Conservation
-20%
-15%
-10%
-5%
0%
Average takeoff thrust reduction (% from full rate)
77
Climb
0 (
Min
fue
l)
B
CI =
Altitude
Max
grad
ien
t
Cost Index = 0 minimizes fuel to climb and
cruise to a common point in space
n
Mi
int
o
oP
t
e
tim
Initial cruise
altitude
B
Cost index
increasing
A
Distance
Fuel Conservation
78
Cruise
Lateral - Directional Trim Procedure
• A plane flying in steady, level flight may require
some control surface inputs to maintain lateraldirectional 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
Fuel Conservation
79
Cruise
Systems Management
• 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
Fuel Conservation
80
Cruise
Winds
• 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
Fuel Conservation
81
Wind Effects On Fuel Mileage
Fuel Mileage =
Ground Fuel Mileage =
NAM
KG
NGM
KG
=
=
VTAS
Fuel Flow
VTAS + VWIND
un
V Gro
d
Fuel Flow
In cruise: positive wind = Tailwind
negative wind = Headwind
NGM/KG
=
NAM
NAM/KG
=
Fuel Used =
NGM
(NGM) (Fuel Flow)
VTAS + VWIND
Fuel Conservation
82
Wind Effects On Cruise Altitude: Wind/Alt Trade
Typical Wind/Altitude Trade Table
33 knots greater tailwind (or,
lower headwind) would be
required at FL310 relative to
FL350 to obtain equivalent
ground fuel mileage
Fuel Conservation
83
Wind Effects On Cruise Altitude: Wind/Alt Trade
Typical Wind Altitude/Trade for Constant Airplane Weight
Example of increasing Tailwind at 31,000 ft
Example of increasing headwind at 35,000 ft
78
78
Wind = 4
0
76
Wind = 3
0
74
35K, Wind =
0
LRC, 35K
Ground fuel mileage
Ground fuel mileage
76
Wind = 2
0
Wind = 1
0
72
31K, Win
d
70
=0
LRC, 31K
68
35K, Wind
=
74
0
LRC, 35K
Wind = -1
0
72
31K, Win
d
70
Wind = -20
=0
Wind = -30
Wind = -4
0
68
LRC, 31K
66
66
64
.80
.81
.82
.83
.84
MACH number
Fuel Conservation
.85
.86
64
.80
.81
.82
.83
.84
.85
.86
MACH number
* Actual ground fuel mileage comparisons vary with airplane model,
weight, and altitudes considered
84
Wind Effects On Cruise Mach Number
Typical affect of wind on ground fuel mileage when
flying a constant altitude and weight
220
Zero wind LRC
100 kt tailwind
200
180
Zero wind
160
C
140
100 kt headwind
LRC
MR
Ground fuel mileage
240
120
100
200 kt headwind
80
60
.72
.73
.74
.75
.76
.77
.78
.79
.80
.81
.82
MACH number
Fuel Conservation
* Actual ground fuel mileage comparisons vary with airplane model,
weight, and altitudes considered
85
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)
Fuel Conservation
86
Descent
Cost Index = 0 minimizes fuel between a common
cruise point and a common end of descent point
A
Min
Final cruise
altitude
0(
Mi
nf
ue
l)
n
poi
from
Altitude
=
e
tim
CI
tA
to B
Cost index
increasing
B
Distance
Fuel Conservation
87
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
Fuel Conservation
88
Summary Of Operational Practices
Flight Operations / Dispatchers
• 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
Fuel Conservation
89
Summary Of Operational Practices
Flight Crews
• 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
Fuel Conservation
90
Maintenance Practices for
Fuel Conservation
Maintenance Personnel
Opportunities For Fuel Conservation
• Airframe maintenance
• Engine maintenance
• Systems maintenance
Fuel Conservation
92
Excess Drag Is Lost Payload
Fuel Conservation
93
Excess Drag Means Wasted Fuel
1% Drag In Terms Of Gallons Per Year
• 747 ≈ 100,000
• 777 ≈ 70,000
• 767 ≈ 30,000
• 757 ≈ 25,000
• 737 ≈ 15,000
• 727 ≈ 30,000
* Assumes typical airplane utilization rates. Actual utilization rates may differ.
Fuel Conservation
94
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
Fuel Conservation
95
Contributors To Total Airplane Drag
(New Airplane at Cruise Conditions)
Pressure, trim and
interference drag
(optimized in the
wind tunnel)
~ 6%
Fuel Conservation
Excrescence drag
(this can increase)
~ 4%
Drag due to
airplane size
and weight
(unavoidable)
~ 90%
* Typical values for illustration purposes. Actual magnitudes vary with airplane model
96
What Is Excrescence Drag?
The additional drag on the airplane due
to the sum of all deviations from a
smooth sealed external surface
Proper maintenance can prevent an
increase in excrescence drag
Fuel Conservation
97
Excrescence Drag On
A ‘New Airplane’ Is Composed Of:
4
3
Excrescence drag
(% airplane drag)
2
Total
Roughness &
surface irregularities
Internal airflow & seal
leakage
Mismatches
and gaps
1
Discrete items
0
Fuel Conservation
* Typical values for illustration purposes. Actual magnitudes vary with airplane model
98
Discrete Items
• Antennas, masts, lights
• Drag is a function of design, size, position
Fuel Conservation
99
Mismatched Surfaces
Steps and gaps at skin joints, around windows, doors,
control surfaces, and access panels
Skin
Frame
Fuel Conservation
100
Internal Airflow
Leaks from higher to lower
pressure areas due to
deteriorated or poorly-installed
aerodynamic seals
Airflow
Fuel Conservation
101
Roughness
(Particularly Bad Near Static Sources)
• Non-flush fasteners, rough surface
• Waviness, gaps
Non Flush Rivet
Waviness
Fuel Conservation
Rough Surface
Gaps
102
Most Important in Critical Areas
• Forward portion of fuselage and nacelle
• Leading areas of wings and tail
• Local Coefficient of Pressure (Cp) is highest
747 Cruise Drag Sensitivities
Outboard aileron up
4” = 1% drag
All spoilers up
3.75” = 2% drag
Rudder deflection
4.5 degrees
(offset 9.5” at base)
=2% drag
Fuel Conservation
1” tall ridge on wing
75 ft. long = 2% drag
103
Regular Maintenance Minimizes Deterioration
• Flight control rigging
• Misalignments and mismatches
• Aerodynamic seals
• Exterior surface finish
• OEW control
• Engine maintenance
• Instrument calibration
Fuel Conservation
104
Flight Control Rigging
Out of rig controls and flaps can cause a large
increase in fuel burn
747-400 examples:
•
•
•
•
Fuel Conservation
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
105
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
Fuel Conservation
106
Misrigged Ailerons
Misrigged outboard ailerons can result
in an increase in drag and fuel flow
Fuel Conservation
107
Spoilers
The spoilers can begin to rise if the aircraft is
balanced by excessive autopilot lateral input
Fuel Conservation
108
Control Surface Rigging Check
747 example (includes fit and fair check):
•
•
•
•
•
Fuel Conservation
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)
109
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
Fuel Conservation
110
Surface Mismatch
Surface Mismatch – ADF Antenna Fairing – negative step
Fuel Conservation
111
Surface Mismatch
Engine inlet secondary inlet door mismatch – positive step
Fuel Conservation
112
Leading Edge Mismatch
727 surface mismatch-R.H. Wing leading edge
slat actuator rod cover - positive step
Fuel Conservation
Airflow
113
Positive Step and Improper Seal
727 surface mismatch - lower wing critical area
(flap track fairing - fabricated leather seal) - positive step
Airflow
Fuel Conservation
114
Check for Tight Aircraft Doors
Note the tight and even fit of the air
conditioning compartment access doors
Fuel Conservation
115
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
Fuel Conservation
Fwd cargo
door seal
depressor
before repair
116
Check for Missing or Damaged Seals
747 R.H. Wing gear well door forward
outboard seal missing and damaged
Airflow
Fuel Conservation
117
Check for Rough Surface Paint
747 rough paint - lower fuselage
Airflow
Fuel Conservation
118
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
Fuel Conservation
119
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
Fuel Conservation
120
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’
Fuel Conservation
121
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
Fuel Conservation
122
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
Fuel Conservation
123
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
Fuel Conservation
124
Engine Components Are Affected By The
Environment In Which They Operate
Fuel Conservation
125
Typical Engine Deterioration Mechanisms
Dirt
accumulation
Increased tip
clearances
Airfoil
erosion
Seal leakage
Fuel Conservation
(Courtesy of Pratt & Whitney)
126
Scheduled Refurbishing Recovers SFC and EGT
SFC
or
EGT
Shop
visit
Shop
visit
Hours or cycles
Fuel Conservation
(Courtesy of Pratt & Whitney)
127
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
Fuel Conservation
(Courtesy of Pratt & Whitney)
128
On-Wing Engine Washing
Regular Intervals Ensure Fuel Economy
• Simple procedure
• Special tooling identified
• 3-4 hours, two mechanics
Hand wash fan and
LPC stator vanes
Up to 1.5% SFC
improvements
possible
Fuel Conservation
(Courtesy of Pratt & Whitney)
129
SFC and EGT Can Be Recovered Between Shop
Visits Using Repetitive Engine Washes
Example of Water Wash Frequency Impact
4.0
1000 cycle wash
3.5
3.0
% ∆TSFC
Unwashed
2.5
2.0
1.5
500 cycle wash
0.75%
1.0
500 cycle wash
cumulative benefit
0.5
0.0
0.5%
0
1000
2000
3000
4000
Cycles
Fuel Conservation
(Courtesy of Pratt & Whitney)
5000
6000
1000 cycle wash
cumulative benefit
130
On-Wing Engine Bleed Rigging
Repair of Leaking Bleed Valves Saves Fuel
• Simple procedure
• Start, stability, service bleeds
• Problem Identified from in-flight
performance trends
Up to 2.5% SFC benefit
possible
Fuel Conservation
(Courtesy of Pratt & Whitney)
131
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
Fuel Conservation
132
Airspeed System Error Penalty
• Keep airspeed system calibrated
• Airspeed reads 1% low, airplane flies 1% fast
• About 2% drag penalty in a 747
Fuel Conservation
133
Check Static Sources
Plugging or deforming the holes in the alternate static port can result
in erroneous instrument readings in the flight deck. Keeping the
circled area smooth and clean promotes aerodynamic efficiency.
Fuel Conservation
134
Proper and Continuous Airframe and Engine Maintenance
Will Keep Your Airplanes Performing at Their Best!
Don’t let this…
Become this!
Fuel Conservation
135
Conclusions
It Takes the Whole Team to Win
• 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
Fuel Conservation
136
For More Information
Boeing has published numerous articles addressing fuel
conservation over the last 4 decades in the following publications:
• 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
Fuel Conservation
137
End of
Fuel Conservation
Flight Operations Engineering
Boeing Commercial Airplanes
November 2004