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Airfield Pavement Roughness -Gaps in the Industry-

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1 Airfield Pavement Roughness -Gaps in the Industry-
ASTM E17 Seminar on Airport Pavement Roughness Issues December 5, 2006 Tony Gerardi APR Consultants, Inc.

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

3 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

4 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 O&S costs, passenger complaints) Whole Aircraft Loading Longer wavelength roughness that excites the whole aircraft (Aircraft fatigue damage, reduces braking ability, reduces pavement life)

5 Runway Roughness Evaluation: A 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 Runway roughness is unique. Gear spacing can be up to 100 feet. Vehicle speeds can be as fast as 150 knots. These two factors can combine to where a 300-foot long event can cause significant aircraft response. Some situations such as multiple event roughness complicate the aircraft response process. And finally, the aircraft’s landing gear are not designed to dampen out the aircraft response to runway roughness. They are principally designed to absorb landing impact.

6 Why Be Concerned About Runway Roughness?
Aborted Takeoff Poor Braking Performance Increased Operational & Support Costs & Aircraft Fatigue Damage Reduces Pavement’s Useful Life and Could Result in Costly Unscheduled Repairs Pilot and Passenger Complaints

7 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

8 Evolution of Airport Pavement Smoothness 16-Foot Straightedge
“Max Deviation Anywhere Along the Length”

9 PI of 5-7 Inches/Mile is Conservative
Evolution of Airport Pavement Smoothness Assessment California Profilograph PI of 5-7 Inches/Mile is Conservative

10 Walking Profilers Sufficient Accuracy for Airfield Evaluation
These three devices are typical of the walking profilers available on the market. Generally, they are suitable accurate for evaluating ride quality. Typically, they emulate the California Profilograph and produce a Profile Index to quantify the roughness. They also generally relay the data in terms of IRI. Only the AR&L unit on the uses aircraft simulation to predict the ride quality of the measure profile. These units range from $20K to $40K in cost. And the inertial profilers can be painfully slow. Sufficient Accuracy for Airfield Evaluation Relatively Inexpensive Can Track All Event Wavelengths Some Units Can be Painfully Slow

11 Inertial Profilers (Measure Relative Profile)
The inertial profilers are much quicker. The van and truck type profiler can operate at highway speeds. They typically report the smoothness of the pavement in IRI. They get extremely detailed measurements (sub millimeter), but in our opinion not needed to adequately identify airfield pavement roughness. What is needed is to track the longer wavelength events, something that these devices can have some problems with. The middle device is called a “lightweight” device and is made to operate on fresh pavements. These device can get expensive. The lightweight units begin at $50K and the vans can cost up to $300K. Van, Truck or ATV Mounted Faster than Walking Type Sub Millimeter Accuracy Texture can Adversely Affect Ride Readings Must Have Room to Accelerate/Decelerate Not as Repeatable As Walking Profilers More Expensive Difficulty Tracking Longer Wavelength Events

12 Other Profilers Rolling Inclinometer Wet or Dry Profiler

13 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) When building a new runway, it should be build with smoothness in mind from the ground up. In the initial work for this design guide handbook, many phases of the design and construction components impact the initial smoothness of the pavement. The smoother the initial smoothness of a a pavement is, the longer that pavement will maintain its smoothness. Things to consider: - Evaluate the design data to ensure the vertical curves or any pavement intersection doesn’t create a ride quality problem. - Measure the profile of the subbase material to identify and remove any long wavelength events - Measure the profile of the completed pavement to ensure that it meets design and that there are no unwanted wavelengths. This survey will also serve as the historic baseline for that runway.

14 IPRF Research Recommended Target Smoothness Values
Rolling Straightedge Length Feet Threshold of Acceptability Inches Pavement Section Length Feet Allowable SSI per Section 5% Must Repair Value for Keel Section .5-Inch Must Repair Value for Outer Lanes 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.

15 No Official Rejection Criteria For Existing Pavements
Unofficial Methods Being Used The Boeing Curve IRI / PI / RN Pilot Reported Roughness Aircraft Simulation There is no official rejection criteria for existing airfield pavements. The industry has developed several methods to try to quantify the rideability of the pavement. - The Boeing Curve - International Roughness Index (IRI) - Pilot Reported Roughness - Aircraft Simulation

16 Case Histories Unnecessary Disputes Evaluating the Design Establish a Baseline Profile

17 Case Histories: Disputes
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

18 Known Rough Runway (Caused Many Pilot Complaints)
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

19 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

20 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

21 Comparing to the Baseline Pavement Profile
2002 Data 1998 Baseline Data Acceptance of an Airport Pavement Should Require an MSL Profile Measurement to Establish a Baseline for Future Measurements Referring to our case study again, this profile shows the baseline profile (bottom) compared to the most recent profile (top). Several areas of change can be identified as the pavement continues it settlement process. Baseline comparison of true profiles allows one to look at the structural integrity of the pavement and the pavement’s subgrade. In the case of HKIA, engineers knew that the pavement would settle, and how much it should settle. They use this technology to ensure all was going according to plan.

22 Quantifying Changes: Settlement
(Feet) Chart Legend Baseline Data (1998) 2001 Data 2002 Data

23 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

24 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

25 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 that’s Agreeable to All Stakeholders

26 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

27 Contact Information… APR’s Website: Or Contact Us By: Tel: (937) Fax: (937)

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