# Presentation: 643150

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

**APR Consultants, Inc.**
**www.aprconsultants.com**

***Airfield Pavement Roughness******-Gaps in the Industry-***

**ASTM E17 Seminar on Airport **
**Pavement Roughness Issues**
**December 5, 2006**

## The Primary Reason We Strive to Build 

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

## 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

## 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)

## 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

**Notes:**
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.

## 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**

## 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**

## Evolution of Airport Pavement Smoothness 16-Foot Straightedge

**“****Max Deviation Anywhere Along the Length”**

## Evolution of Airport Pavement Smoothness AssessmentCalifornia Profilograph

**PI of 5-7 Inches/Mile is Conservative**

## Walking Profilers

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

**Notes:**
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.  

## 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

**Notes:**
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.

## Other Profilers

**Rolling Inclinometer**

**Wet or Dry Profiler**

## 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)

**Notes:**
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.

## 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.

## No Official Rejection CriteriaFor Existing Pavements

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

**Notes:**
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

## Case Histories

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

## 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**

## Comparison of Runway in Western US to Known Smooth and Known Rough Runway

**Known Rough Runway (Caused Many Pilot Complaints)**

**Very Smooth New PCC Runway (No Pilot Complaints)**

_**Case History**_

**Runway in Western US**

## 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

## 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

## Comparing to the Baseline Pavement Profile

**Acceptance of an Airport Pavement Should Require an MSL**
** ****Profile Measurement to Establish a Baseline for Future Measurements**

**Notes:**
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.

## Quantifying Changes: Settlement

## 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

## 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

## 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

## 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

- Establish Official Rejection Criteria That Defines When an Airport Pavement has Become _Too_ Rough.
- Establish a Standard for Evaluating Pavement Roughness

- Conclusions(Gaps in the Industry)

## Contact Information...

- APR’s Website:
- 	www.aprconsultants.com
- Or Contact Us By:
- 	email:	info@aprconsultants.com
- 	Tel:		(937) 849-6795
- 	Fax:	(937) 849-6048