Tony Gerardi

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Airfield Pavement Roughness-Gaps in the Industry-
ASTM E17 Seminar on Airport Pavement Roughness
Issues December 5, 2006

• Tony Gerardi
• APR Consultants, Inc.
• www.aprconsultants.com

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The Primary Reason We Strive to Build and
Maintain Smooth Pavements is to Minimize
Aircraft Dynamic Response and Maximize Aircraft
Performance
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Presentation Overview

• Why Smoothness is Important
• Acceptance of New Pavements (FAA AC 150/5370
  16-Foot Straightedge)
• Rejection Criteria (Existing Pavements)
• Case Histories
• Gaps in the Industry

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Roughness Defined

• Shock Loading
• Short wavelength roughness that is too fast for
  the tires and suspension system to react.
  (rattles instruments, jars avionics)
• Single Axle Loading
• Short wavelength roughness that the tires and
  suspension system is capable of reacting to.
  (Increases OS costs, passenger complaints)
• Whole Aircraft Loading
• Longer wavelength roughness that excites the
  whole aircraft (Aircraft fatigue damage, reduces
  braking ability, reduces pavement life)

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Runway Roughness EvaluationA Unique Problem

• Landing Gear Spacing of nearly 100 Feet
• Speeds up to 150 Knots
• Aircraft will Respond to Bumps 300 Feet Long or
  Longer
• Multiple Bumps in Succession Non-Linear Effect
• Struts are Primarily Designed for Landing Impact

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Why Be Concerned About Runway Roughness?
Aborted Takeoff
Poor Braking Performance
Increased Operational Support Costs Aircraft
Fatigue Damage
Reduces Pavements Useful Life and Could Result
in Costly Unscheduled Repairs
Pilot and Passenger Complaints
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FAA AC 150/5370 (the P-501 Spec)New Pavement
Acceptance

• Criteria
• .25 Inch in 16 Feet or PI of 5-7 (in/mile)
• .5 Inch Max Deviation from Design Grade
• Difficult to Meet 100 of the Time
• Conservative from Aircraft Response Perspective
• Can be a Source for Disputes Regarding Pavement
  Acceptance
• Unnecessary Grinding
• Led to IPRF/FAA Research Project

Note Grade Control in the Same as Vehicle
Response Control
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Evolution of Airport Pavement Smoothness 16-Foot
Straightedge
Max Deviation Anywhere Along the Length
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Evolution of Airport Pavement Smoothness
AssessmentCalifornia Profilograph
PI of 5-7 Inches/Mile is Conservative
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Walking Profilers

• Sufficient Accuracy for Airfield Evaluation
• Relatively Inexpensive
• Can Track All Event Wavelengths
• Some Units Can be Painfully Slow

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Inertial Profilers (Measure Relative Profile)

• Van, Truck or ATV Mounted
• Faster than Walking Type
• Sub Millimeter Accuracy
• Texture can AdverselyAffect Ride Readings

• Must Have Room to Accelerate/Decelerate
• Not as Repeatable As Walking Profilers
• More Expensive
• Difficulty Tracking Longer Wavelength Events

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Other Profilers
Rolling Inclinometer
Wet or Dry Profiler
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Considerations for Building New Airport Pavements

• Evaluate the Design for Aircraft Response
• Measure Profile for Smoothness at Each Stage of
  Construction
• Maintain String Line Tension
• Measure Profile for Smoothness soon after
  Placement (Feedback to Paving Crew)
• Final MSL Measurement Serves as Baseline for
  Tracking Change for That Pavement (Deliverable)

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IPRF Research Recommended Target Smoothness
Values

• Rolling Straightedge Length 25 Feet
• Threshold of Acceptability .35 Inches
• Pavement Section Length 500 Feet
• Allowable SSI per Section 5
• Must Repair Value for Keel Section .5-Inch
• Must Repair Value for Outer Lanes .75-Inch
• Note 1 Repeated bumps (3 or more) in the keel
  section .25 inches or greater will require
  repair.
• Note 2 Any longitudinal step bump greater than
  .25-inch in the keel section will require repair.
• Note 3 Exceptions apply for intersecting
  runways, drains on taxiways and ramps.

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No Official Rejection CriteriaFor Existing
Pavements

• Unofficial Methods Being Used
• The Boeing Curve
• IRI / PI / RN
• Pilot Reported Roughness
• Aircraft Simulation

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Case Histories

• Unnecessary Disputes
• Evaluating the Design
• Establish a Baseline Profile

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Case Histories Disputes

• Case Histories
• Military Parking Apron in Eastern US (Relax Grade
  Control Requirements at Very Low Speeds)
• Taxiway in Midwest (Straightedge Deviation)
• Runway in Southern US (Unnecessary Grinding)
• Runway in Western US (Grade Control Issue)
• Current P-501 Puts All Stakeholders in an Awkward
  Position

Note Grade Control is Not Vehicle Response
Control
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Runway in Western US
Known Rough Runway (Caused Many Pilot Complaints)
Case History
Very Smooth New PCC Runway (No Pilot Complaints)
Comparison of Runway in Western US to Known
Smooth and Known Rough Runway
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Case History Evaluate the Design Using Aircraft
Simulation

• Design Constraints can cause the Design to
  Produced Unacceptable Aircraft Response
• Midwest Runway, (built to design unacceptable)
• Middle East and Orange County CA Correction
  made to the design.
• Intersecting Runways at Manitoba, in Texas, and
  in NY
• Optimize Drainage and Roughness
• Minimize the Impact on the Primary Runway

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Case History Settlement

• Measure Mean Sea Level (MSL) Profile Before
  Pavement Opens to Traffic
• Use Data for Final Pavement Smoothness Acceptance
• Use Data to Establish Baseline
• Track Settlement Periodically by Comparing MSL
  Profiles

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Comparing to the Baseline Pavement Profile
Acceptance of an Airport Pavement Should Require
an MSL Profile Measurement to Establish a
Baseline for Future Measurements
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Quantifying Changes Settlement
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Roughness and Stopping Distance

• It Takes More Runway to Stop on a Rough Runway
• Varies the Normal Load
• Tricks the Anti-skid
• Difficult to Maintain Steady Brake Pressure
• Wheel Hop
• Can Make the Difference Whether or not the
  Runway is Overrun
• When Landing Long
• Stopping on a Contaminated Runway
• or in a High Speed Abort

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The High Speed Aborted Takeoff

• Aircraft is Heavy, Speed is High, Little Runway
  Remaining
• Hot Brakes (Blown Tire Fuse Plugs and Fire
  Hazard)
• High Nose gear Loads (Blown Fuse Plugs or Failed
  Drag Brace)
• Risk Overrunning the Runway

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Conclusions(Gaps in the Industry)

• Define the Effect of Roughness on Aircraft
  Braking Performance
• Quantify the Effect of Roughness on Dynamic Loads
  in a High Speed Aborted Takeoff
• Update New Pavement Acceptance Criteria thats
  Agreeable to All Stakeholders

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Conclusions(Gaps in the Industry)

• Require a Baseline MSL Profile as a Deliverable
  for Future Comparisons
• Establish Official Rejection Criteria That
  Defines When an Airport Pavement has Become Too
  Rough.
• Establish a Standard for Evaluating Pavement
  Roughness

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Contact Information

• APRs Website
• www.aprconsultants.com
• Or Contact Us By
• email info_at_aprconsultants.com
• Tel [phone]
• Fax [phone]