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FLIGHT
OPERATIONSENGINEERING
1For Training Purposes Only Copyright © 2009 Boeing. All rights reserved
Runway Loading
John ChristyPerformance Engineering Operations
Flight Operations EngineeringBoeing Commercial Airplanes
September 2009
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2For Training Purposes Only Copyright © 2009 Boeing. All rights reserved
Performance Limits
1. Field Length Limit2. Climb Limit
3. Obstacle Limit
4. Tire Speed Limit5. Brake Energy Limit
6. Pavement Strength Limit
7. Airport Noise Limit
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3For Training Purposes Only Copyright © 2009 Boeing. All rights reserved
Relationship of Aircraft to Pavement
• Loading the pavement
• Rating the pavement
• Life of the pavement
• Runway Roughness
• Ongoing Research
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4For Training Purposes Only Copyright © 2009 Boeing. All rights reserved
Pavement Loading
• Pavement loading refers to the load an airport runway,taxiway, or ramp area is subjected to by the airplane’s
main landing gear.
• About 2/3 of the worlds larger airports have flexiblepavement runways.
FlexiblePavement
Asphalt
Base/ Subbase
Natural Soil
Rigid
Pavement
Concrete
Base/ Subbase
Natural Soil
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Runway Loads - Takeoff / LandingTypical Jet Aircraft
Distance
Runway pavements are designed for static load.
The impact of landing is only about 38% of the takeoff static load.
R u n w a y
l o a d % m a x t a x i
100
80
60
40
20
0
TAKEOFFLANDING
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Insufficient Pavement Strength?
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Not Typical Failure
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Typical Result of Pavement Overload
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Pavement Rating
Purpose of the Pavement Rating
• To match the aircraft traffic with the pavementso that the design life is reached.
• To assure a practical, economical pavement life.
• To provide a convenient method of comparingaircraft loads to allowable pavement capacity.
• Today, many if not most, airports publish out of date pavement ratings! Such ratings areusually lower than the true pavement strength.
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Pavement Rating
• Pavement rating is derived from: – An evaluation of the pavement through
engineering tests and traffic history, or
– Optionally, the aircraft currently using the airport.
(Note: the pavement could be stronger).• Pavement engineering is a complex subject.
• Airplane safety is not involved.
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Pavement Rating
• Pavement Rating Types: – ESWL: Equivalent Single Wheel Load – Obsolete
– LCN: Load Classification Number – Obsolete
– AUW: All Up Weight – Obsolete
– FAA: All Up Weight by Gear type
– ACN/PCN: ICAO Standard since 1981
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Pavement Rating
• ACN (Aircraft Classification Number):Describes the relative load intensity of an airplane’smain landing gear.
What is ACN?
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Aircraft Rating
Basis for ACN
• ACN was adopted by ICAO and member nations asthe official method for reporting a relative comparisonof airplane loading intensity.
• ACN replaces all previous methods by whichmanufacturers report their aircraft loadingcharacteristics.
• ACN is not pavement design.
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14For Training Purposes Only Copyright © 2009 Boeing. All rights reserved
Aircraft Classification Number – ACN
The ACN’s of an airplane are calculated as follows:
• The Portland Cement Association computer program “PDILB” is used to calculatethe concrete thickness required for standard conditions using:
Standard
Conditions
• Basic airplane characteristics
• Concrete working stress = 2.75 MN/m² (400 PSI)
• Concrete Modulus of Elasticity E = 27,580 MPa (4,000,000 PSI)
• Reference thicknesses are calculated for the 4 standard subgrade K values.A standard rigid pavement chart with the reference thickness is then used to find ACN.
• The U.S. Corps of Engineers method S-77-1 is used to calculate the pavementthicknesses required for standard conditions using:
Standard
Conditions
• Basic airplane characteristics
• 10,000 coverages
• Reference thicknesses are calculated for the 4 standard subgrade CBR values
• A standard flexible pavement chart with the reference thickness is then used to find ACN
Flexible
The basic airplane characteristics used above are:
Gear Load
Gear Geometry
Tire Pressure
• Max. aft C.G. limit at max. gross weight is used for all weights
• Number of wheels and spacing
• As published by manufacturer
Rigid
ONLY Aircraft Manufacturers Calculate ACN's!
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15For Training Purposes Only Copyright © 2009 Boeing. All rights reserved
Pavement Rating
What is PCN?
• PCN (Pavement Classification Number): Describesthe actual load-carrying capacity of an airportrunway, taxiway or ramp
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Pavement Rating
Basis for PCN
• PCN was adopted by ICAO and member nations as theofficial method for reporting airport pavement strength.
• PCN replaces all previous methods by which airport
authorities report their pavement capabilities.
• PCN is not pavement design.
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Pavement Classification Number – PCN
Airport authority evaluates pavement by any means and determines the gross weight limit of a critical airplane which willresult in the desired pavement life at the expected traffic level.
Data reported (published in AIP) examples: PCN 50 RCXT or 37 FBYU
• PCN
• Pavement type
A number from 1 to 100 or larger; a PCN 100 pavement is
stronger than a PCN 90 pavement, assuming the same
pavement type and subgrade category.
• Subgrade category
Code
A (High)
B (Medium)
C (Low)D (Ultra low)
CBR Range
Above 13
8 to 13
4 to 8Less than 4
Standard
15
10
63
Standard
150
80
4020
Modulus K Range
Above 120 MN/m3
60 to 120 MN/m3
25 to 60 MN/m3
Less than 25 MN/m3
• Default value - code B will be assumed if subgrade is not specified.
• Tire pressure Due to local conditions, airport authority may choose to specify a tire pressure limit(usually applicable to thin asphalt surfaces)
– Code W - No tire pressure limit
– Code X - 1.5 Mpa maximum (218 PSI) – Code Y - 1.0 Mpa maximum (145 PSI)
– Code Z - 0.5 Mpa maximum (73 PSI)
Default value - code X will be assumed if tire pressure limit is not specified
Code T - Technical evaluation
Code U - Based on experience from using aircraft
• Method of evaluation
Code F - Flexible Code R - Rigid
ONLY Airport Authorities Publish PCN's!
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18For Training Purposes Only Copyright © 2009 Boeing. All rights reserved
PCN ACN72RBWT
Rating Number
2 types of Pavement
4 strengths of soil support 4 tire pressure ranges
2 types of basis for evaluation
ACN ≤ PCN means Unrestricted MTOW
Pavement Rating
What is ACN/PCN?
• ACN (Aircraft Classification Number): Describesthe relative load intensity of an airplane’s mainlanding gear.
• PCN (Pavement Classification Number): Describesthe actual load-carrying capacity of an airport
runway, taxiway or ramp.
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Pavement Rating
• ACN’s are determined by airplane manufacturers:
– Published in Airplane Characteristics for AirportPlanning documents.
– Also shown in ICAO Annex 14 and Jeppesen.
• PCN’s are established by the airport authoritiesof the various nations:
– Published in the Aeronautical Information Publications (AIP).
– Also shown in the Jeppesen Airport Directory.
– Airports are the only authority to allow or disallow aircraftusage of the pavement.
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PCN Data: Jeppesen Example
3 Airports All: PCN 56/F/A/W/T
Abha (OEAB) PCN 56 F/A/W/T
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Boeing Airport Technology: ACN Data
Airport Planning Manuals Availablewww.boeing.com/airports
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ACN Data
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ACN Data
Abha (OEAB) PCN 56 F/A/W/T
715,000 lbs (325 tonnes)
660,000 lbs (300 tonnes)
PCN 56 FBXT
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ACN Data
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PCN Data: AIP Example
Brasil Free AIP data online: see
http://www.aisweb.aer.mil.br/aisweb/
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Brasil Free AIP data online: see
http://www.aisweb.aer.mil.br/aisweb/
PCN Data: AIP Example
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Brasil Free AIP data online: see
http://www.aisweb.aer.mil.br/aisweb/
PCN Data: AIP Example
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Brasil Free AIP data online: see
http://www.aisweb.aer.mil.br/aisweb/
PCN Data: AIP Example
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Brasil Free AIP data online: see
http://www.aisweb.aer.mil.br/aisweb/
PCN Data: AIP Example
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Pavement Life
• Typical pavement design life is 20 years.
• Pavement life is a function of original design, number of aircraft operations, aircraft loads, and maintenance.
• Historically, pavements increase in load carryingcapacity by the following:
– Rigid pavements are reconstructed periodically toaccommodate heavier aircraft.
– Flexible pavements are typically overlaid every 10 to
14 years on average (primarily to correct for weathering). Each overlay adds life to the pavementbecause it increases the cross-sectional thickness.
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Pavement Life
ICAO Simplified Pavement Life Criteria
• For flexible pavements, occasional movements by aircraftwith ACN not exceeding ten percent above the reportedPCN should not adversely affect the pavement life.
• For rigid, occasional movements by aircraft with ACN not
exceeding five percent above the reported PCN should notadversely affect the pavement life.
• If the pavement structure is unknown, the five percentlimitation should apply to both cases above; and
• The annual number of overload movements in all casesshould not exceed approximately five percent of the totalannual aircraft movements.
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Pavement Life
777 Flexible Pavement Life
Shows the effect of a 2-inch overlay on pavement life
PCN 59 FB
t-=32”
20
30
40
50
60
70
80
ACN
300 400 500 600 700 800
Gross weight, 1,000 lb
20
30
40
50
60
70
80
100 1,000 10,000 100,000 1,000,000
Annual Departures
PCN
Example Pavement
CBR 10 Subgrade
20-year Pavement Life
S-77-1 Design
t=30”
5,000 15,000
777-300ER
Code B Subgrade
ACN Program
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777 Rigid Pavement Life
Shows the effect of a 1-inch increase in thickness on pavement life
30
40
50
60
70
80
90
ACN
300 400 500 600 700 800
Gross weight, 1,000 lb
30
40
50
60
70
80
90
100 1,000 10,000 100,000 1,000,000
Annual Departures
PCN
Example Pavement
K= 300 pci Subgrade
20-year Pavement Life
PCA Design
T=14”
777-300ER
Code B Subgrade
ACN Program
PCN 74 RB
T=15”
1,300 4,200
Pavement Life
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346767.34 Gervais
Runway Roughness: Alaskan Bump
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Long Wave Roughness
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Effect of Excessive Roughness
MAY:
– Affect instrument readability for pilot
– Affect steering control
– Reduce landing gear and aircraft
structural life – Impose a .4g vertical acceleration force
on the aircraft
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Boeing Runway Roughness Criteria
Bump length, m
Bump height, cm
Acceptable
0 10 20 30 40 500
5
10
15
20
Excessive
60
RUNWAY ROUGHNESS CRITERIAL
H
L
H
L
H
Unacceptable
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Ongoing Research- NAPTF Test Machine
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Summary
• Pavement strength ratings, when properly analyzed andpublished, will allow:
1) pavement to support the expected aircraft traffic for the desired design life (normally 20 years).
2) airlines to optimize aircraft operations to eliminateunnecessary weight restrictions (payload penalties).
3) airlines evaluate the viability of prospective airportsas potential destinations.
• Many airports worldwide currently publish out of date(artificially low) pavement strength ratings.
• Boeing Airport Technology is available to help resolvethese issues. Pavement Ratings are not absolute.
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