Runway Loading

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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




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




Relationship of Aircraft to Pavement

• Loading the pavement

• Rating the pavement

• Life of the pavement

• Runway Roughness

• Ongoing Research




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




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




Insufficient Pavement Strength?




Not Typical Failure




Typical Result of Pavement Overload




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• Today, many if not most, airports publish out of date pavement ratings!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.




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.




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




Pavement Rating

• ACN (Aircraft Classification Number):Describes the relative load intensity of an airplane’smain landing gear.

What is ACN?




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.




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!




Pavement Rating

What is PCN?

• PCN (Pavement Classification Number): Describesthe actual load-carrying capacity of an airportrunway, taxiway or ramp




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.




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!




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.




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.




PCN Data: Jeppesen Example

3 Airports All: PCN 56/F/A/W/T

Abha (OEAB) PCN 56 F/A/W/T




Boeing Airport Technology: ACN Data

Airport Planning Manuals Availablewww.boeing.com/airports




ACN Data




ACN Data

Abha (OEAB) PCN 56 F/A/W/T

715,000 lbs (325 tonnes)

660,000 lbs (300 tonnes)

PCN 56 FBXT




ACN Data




PCN Data: AIP Example

Brasil Free AIP data online: see

http://www.aisweb.aer.mil.br/aisweb/




























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.




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.




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




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




346767.34 Gervais

Runway Roughness: Alaskan Bump




Long Wave Roughness




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




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




Ongoing Research- NAPTF Test Machine




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.

Documents

Runway Loading