Smoothness to RoughnessTechniques, Tips and 26 Years of Insight

Michael Gerardi

APR Consultants, Inc.

The Primary Reason We Strive to Build

and Maintain Smooth Pavements is to Minimize Aircraft Dynamic Response and to Maximize Aircraft and Pavement Performance.

Courtesy F. Seggie

Smoothness Acceptance Testing

New Pavement Acceptance Specifications –Grade Control

• Responsible for Long Wavelength “Smoothness”

• .5-Inch Maximum Deviation from Design

-15

-10

-5

0

5

10

15

20

25

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Full Length Centerline, 2013

Ele

vati

on

(in

)

Distance (feet)

APR’s Experience With Smoothness Criteria

• Criteria▫ .25-Inch to a 12-Foot Straightedge (FAA) or 3mm in a 3-

Meter Straightedge (ICAO)

▫ PI of 15 Inches per Mile (Profilograph)

• From an Aircraft Ride Quality Perspective▫ Generally these Thresholds are Overly Conservative

These Methods Apply to Construction Quality. As a Result, Their Usefulness to Identify Roughness That Affect Aircraft Response is Limited.

Types of Roughness

• Shock Loading▫ Elevated Slabs or Spalling

• Single Axel Loading▫ Short to Medium Wavelength

▫ Multiple Events in Succession

• Whole Aircraft Loading▫ Long Wavelength Event

▫ Up to 300 Feet (91m) Long

Methods to Evaluate RoughnessMethod Very Short WL

Shock LoadingShort WL

Single AxleLong WL

Whole Aircraft

Visual (PCI)

Drive by in Car

Pilot Reported

Physical Straightedge

California Profilograph

IRI

BBI

Analytical Straightedge

Aircraft Simulation

Forget About What You Know.

Change Your Perspective.

Keep the Aircraft in Mind

85 Feet (26m)12-Foot Straightedge

Boeing 777-200

25-Foot Profilograph

IRI (Quarter-Car Model)

Old Technology Vs New Aircraft

Current Smoothness Acceptance Testing Devices and Methods Do not Identify Long Wavelength Events that Can

Affect Aircraft Dynamic Response

Dispute Case Study

• New Asphalt Overlay

• Owner Concerned About Higher PI Values

• What Effect Will it Have on Aircraft Ride Quality?

Start

Distance

(ft)

Stop

Distance

(ft)

Profile

Index

17 528 7.23

529 1,056.00 1.00

1,057.00 1,584.00 0.00

1,585.00 2,112.00 2.00

2,113.00 2,640.00 4.51

2,641.00 3,168.00 2.00

3,169.00 3,696.00 1.50

3,697.00 4,224.00 5.51

4,225.00 4,752.00 0.50

4,753.00 5,280.00 3.51

5,281.00 5,808.00 2.00

5,809.00 6,336.00 2.00

6,337.00 6,864.00 3.51

6,865.00 6,938.00 30.46

Dispute Case Study

0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000 6000 7000

Runway 02-20

Ele

vati

on

(in

)

Distance (feet)

PI = 7.23

PI = 30.46

Dispute Case Study

-1

0

1

-1

0

1

0

20

0 1000 2000 3000 4000 5000 6000 7000

0.4

-0.4

0.4

-0.4

Taxi: Boeing 737-800 Aircraft 172500 lbs GW95-Knot Constant Speed Taxi

Air Temperature = 59 (°F) Field Elevation = 0 (ft) Headwind = 0 (kts)Profile Filename = Line J - 90 West.dat Sim. Start = 0 (ft) RQF = 2.407217Output Filename = Sim1.out Taxiing Speed = 95 (knots) Complete Simulation = Yes

Pilo

t St

a V

ert

Acc

(g'

s)C

G V

ert

Acc

(g'

s)El

eva

tio

n (

in)

Distance (feet)

The Problem with Indexes

• Aircraft Response is Complex

• Indexes Can Not Take Into Account the Variability of the Situation▫ Aircraft Size

▫ Aircraft Speed

▫ Location on The Runway

▫ Operation Type

• One Generalized Number Can Mischaracterize the Event in Question

The Problem with Indexes

• Imagine You Encounter a Speed Bump while Driving Your Car▫ Encountered at 3 mph - No

Worries

▫ Encountered at 50 mph - It Would Be a Problem!

• Indexes Don’t Take Speed into Account

New Tools You Can Use

• Understanding that New Pavements Should Meet Smoothness Guidance / Criteria▫ There Are Devices and Methods that can Evaluate the

Pavement for Smoothness AND Help Evaluate Airfield Pavements for Content That Affects Aircraft Response.

▫ APPROVED in FAA AC 150-5370-10H

Various Profiling Devices

▫ Sufficient Accuracy for Airfield Evaluation▫ Relatively Inexpensive▫ Can Track All Event Wavelengths▫ Some Units are Slow to Operate

Inclinometers

Various Profiling Devices

▫ Van, Truck or ATV Mounted▫ Faster Than Walking Type▫ Sub Millimeter Accuracy▫ Texture Can Adversely

Affect Ride Readings

▫ More Expensive▫ Difficulty Tracking Longer

Wavelengths▫ Requires Accel / Decel Room▫ Will not Measure Grade

Inertial Profilers

Various Profiling Devices

▫ Captures “True” Profile▫ Can Be Faster than

Inclinometer▫ Millimeter Accuracy▫ Texture is Not Detected

▫ Very Repeatable▫ Wide Range of Prices

Depending upon the Unit

External Reference Profilers

Robotic Total Station Scanning Laser

Walking External Reference

Limitations of a Physical Straightedge

• Profile Index (PI)▫ Effective for Short Wavelength. Misses Long

Wavelength Content.

• 12-Foot Straightedge (3-Meter)▫ Effective for Short Wavelength. Misses Long

Wavelength Content.

• Analytical Straightedge▫ Uses Any Length Straightedge. Effective for All

Wavelengths.

Straightedge Comparison

2 Inches

120 Feet

Straightedge Comparison

Straightedge Comparison

Additional Evaluation Methods

• Boeing Bump Index▫ Can Be Used as a “First Look” Method

▫ Is Limited in What it Can Accurately Identify It’s an Index

▫ Can Produce False Sense of Security

• Aircraft Simulation▫ Detects Short and Long Wavelength Events

▫ Not Subjective

Thresholds of Acceptability

• .40G in Vertical Response is an Unofficial Threshold of Acceptability

▫ Shock and Vibration and Human Discomfort

Shock and Vibration Handbook, Chapter 44 “Effects of Shock and Vibration on Man” by D. E. Goldman and H. E. Von Gierke

▫ Boeing Study on Structural Fatigue

Boeing Report D6-81746

Boeing’s Levels of Roughness Based on Accelerations at the Aircraft’s CG

• Level 1 Roughness▫ .25G to .54G

▫ Acceptable

• Level 2 Roughness▫ .55G to .79G

▫ Excessive

• Level 3 Roughness▫ .80G and Up

▫ Unacceptable

Boeing Criteria

• Acceptable – Minor impact on aircraft fatigue damage and minimal passenger discomfort

• Excessive – Pavement repair recommended. Immediate closure not required

• Unacceptable – Immediate closure of the affected pavement

Predicting an Aircraft’s Response

• Aircraft Simulation is Used to Predict Responses at the Pilot’s Station and the Aircraft’s CG to the Measured Profile.

Concerns With BBI

Because BBI is a Simple Wavelength Vs. Amplitude

Evaluation Tool, It Cannot Detect Multiple Events

Pavement Roughness

Takeoff with Roughness in the Overrun

-1

0

1

-1

0

1

0

2.5

5.0

0 500 1000 1500 2000 2500 3000 3500 4000

0.4

-0.4

Takeoff: Boeing 737-800 Aircraft 172500 lbs GWRoughness in the Overrun

Air Temperature = 59 (°F) Headwind = 0 (kts)Field Elevation = 0 (ft) RQF = 2.996531Sim. Start = 0 (ft)

Pilo

t St

a V

ert

Acc

(g'

s)C

G V

ert

Acc

(g'

s)El

eva

tio

n (

in)

Distance (feet)

Takeoff with Roughness at 2,000 Feet

-1

0

1

-1

0

1

0

2.5

5.0

0 500 1000 1500 2000 2500 3000 3500 4000

0.4

-0.4

Takeoff: Boeing 737-800 Aircraft 172500 lbs GWRoughness Beginning at 2,000 Ft

Air Temperature = 59 (°F) Headwind = 0 (kts)Field Elevation = 0 (ft) RQF = 3.951038Sim. Start = 0 (ft)

Pilo

t St

a V

ert

Acc

(g'

s)C

G V

ert

Acc

(g'

s)El

eva

tio

n (

in)

Distance (feet)

A Runway’s Profile Changes Over Time

Settlement of a Concrete Runway

2006

2010

2014

3.50 Inches

4.50 Inches

1.0 Inch

Settlement of a PCC Runway

0

2

0

2

0

2

0 1000 2000 3000 4000 5000 6000 7000 8000

Ele

vati

on

(in

)El

eva

tio

n (

in)

Ele

vati

on

(in

)

Distance (feet)

CVG 18R CL, 2005 Baseline CVG 18R Centerline 2013 CVG 18R Centerline 2017Pavement Settlement over 12 Years

2013 Update Profile

2005 Baseline Profile

2017 Update Profile

Downward Spiral of Ride Quality• Overtime, the Pavement’s Profile Shape Can Change

• Depending upon the Wavelength, Aircraft Begin to Respond to These Changes – Increasing Dynamic Loading

• Deteriorating Ride Quality Produces More Pavement Roughness

Integrate Profile Monitoring into PMS

• Using Profile Measurement Devices Discussed in this Presentation, Changes to the Profile can be Tracked

• Like Other PMS Elements, Measure and Assess Periodically

▫ 3-5 Years

• Allows Managers to Predict Problems and Manage Maintenance

Wrap Up

• Existing Guidance and Criteria Will Provide you with Degrees of “Smoothness”

• Limitations in the Methods and Devices Allowable Will Not Identify “Roughness”

• Newer Technology Profiling Devices Will Provide You With Answers for Both - Smoothness and Roughness

Wrap Up

• Devices that Capture “True” Profile have Proven Very Useful in Tracking Profile Shape

• Profile Shape Changes Appear to be Common Place As the Pavement Ages

• Shape Changes can Create Roughness and Poor Aircraft Response

• Airports are Choosing to Enhance their PMS using Profile Monitoring Services.

The End