Adf Friction Policy Manual

ADF FRICTION POLICY MANUAL

DEVELOPED BY:

DIRECTORATE OF ESTATE ENGINEERING POLICY

CIVIL ENGINEERING SECTION

Version 1.2: May 2011

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Revision History

Version / Date / Author / Details
1.0 / 2004 / SQNLDR Sheldon Krahe / Initial DRAFT
1.1 / 2010 / SQNLDR Danny Cusack / Finalised DRAFT. Set initial testing frequency.
1.2 / 5/2011 / SQNLDR David Alder / Edited. Changed some testing frequencies.
Added Albatross, Woomera and Oakey.

Version 1.2: 3 May 2011

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EXECUTIVE SUMMARY

1.  This document provides policy guidance on how Defence manages friction on its sealed runways. It is a management tool to ensure that Defence-owned runways are maintained in a functional and safe condition.

2.  Defence will conduct a National Friction Testing Program for up to 14 ADF airfields across Australia; principally those airfields with RPT flights where the Civil Aviation Safety Authority (CASA) requires testing be conducted plus ADF airfields with large wide-bodied aircraft home-based at that establishment. The frequency of friction testing depends on the type and mix of aircraft, surface texture characteristics, severity of rubber build up, pilot reports of low friction during braking, recent overlay of surface and past results.

3.  Friction testing will be undertaken using a Griptester (or other device approved by ICAO such as the Mu-Meter) at two test speeds of 65km/h and 95km/h and shall be conducted at both 3 meters and 6 metres from the runway centreline. A calibration strip shall be established at each airfield. Friction testing shall be performed on all newly constructed or re-sheeted runway pavement surfaces within one year. The proposed maintenance intervention levels[1] that will be adopted by Defence for the Griptester (or Mu-Meter) are given below.

65 km/h Test / 95 km/h Test
Friction Level / Minimum Friction Level / Maintenance Planning Level / New Design / Construction / Minimum Friction Level / Maintenance Planning Level / New Design / Construction
Griptester / 0.43 / 0.53 / 0.74 / 0.24 / 0.36 / 0.64
Mu Meter / 0.42 / 0.52 / 0.72 / 0.26 / 0.38 / 0.66

Table 1: Friction Level Classification for Runway Pavement Surfaces

4.  If the results of testing indicate that friction has deteriorated below the Maintenance Planning Level for two consecutive 100m sections, Defence Support Group (DSG) shall plan rubber removal works for the affected touchdown zone within the next 60 days.

5.  If the results of testing indicate that friction has dropped below the Minimum Friction Level for any 100m segment & the adjacent 100m segments are below the maintenance planning friction level, DSG shall plan rubber removal works for the affected touchdown zone within the next 14 days. A NOTAM must be promulgated that advises that the runway pavement falls below the minimum friction level when wet.

Version 1.2: 3 May 2011

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TABLE OF CONTENTS

Introduction 1

Regulatory Framework 1

OBJECTIVES OF FRICTION TESTING 2

Runway Surface Standards 2

Importance of Adequate Runway Friction 2

Factors that Affect Runway Friction 3

Coefficient of Friction – Definition 4

Methods of Friction Testing 4

ADF Friction Testing Frequency 4

Table 2: ADF Establishments – Friction Testing Frequency 5

Griptester 6

Methodology for Friction Testing 6

Reporting of Runway/Tyre Friction Values 7

Intervention Levels 7

Rubber Contamination of Runway Pavements 8

Rubber Removal 8

Methods of Rubber Removal 8

ADF Establishment Requirements / testing conditions 9

Reporting 9

Version 1.2: 3 May 2011

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Introduction

1.  This manual addresses the frequency at which Defence will undertake friction testing on its runways and also sets the intervention levels for the removal of rubber in the touchdown zones. The guidance outlined in this manual will ensure ADF conformance with the Civil Aviation Safety Authority’s Manual of Standards Part 139 (MOS139).

2.  Policy guidance issued by such bodies as the International Civil Aviation Organisation (ICAO) and the US Federal Aviation Administration (FAA) has been considered by Defence in formulating this policy manual. In particular, FAA Advisory Circular 150/5320-12C has been utilised in setting maintenance intervention levels.

3.  An important difference between the guidelines in the FAA Advisory Circular 150/5320-12C and the requirements of this manual is that results are to be reported every 100m instead of every 500ft (152.4m).

Regulatory Framework

4.  Civil Aviation Safety Regulations (CASR) Part 121A and Part 121B require aeroplanes conducting air transport operations to operate from aerodromes meeting the requirements of CASR Part 139.

5.  The CASA Manual of Standards Part 139 states:

[10.15.2.3] From January 2006, designated international aerodromes with runways serving code 4 jet aeroplanes, conducting international air transport operations, will be required to use an ICAO accepted continuous friction measuring device with self-wetting features to measure the friction level of the runway.

[10.15.2.4] Runways must be evaluated when first constructed or after resurfacing to determine the wet runway surface friction characteristics.

[10.15.2.5] Friction measurements must be taken at intervals that will ensure identification of runways in need of maintenance or special surface treatment before the surface conditions deteriorate further. The time interval between measurements will depend on factors such as: aircraft type and frequency of usage, climatic conditions, pavement type, and maintenance requirements.

6.  MOS139 does not specify the time interval between measurements but leaves it to the airport operators to determine the inspection frequency based on their unique operating environment and traffic levels.

7.  Formalised ‘Joint User Deeds’ with commercial airport operators apply at Darwin and Townsville. There are also other Defence airfields used by civilian operators on a permissive use lease basis at Williamtown (Newcastle, NSW), Tindal (Katherine, NT) and Learmonth, (Exmouth, WA). These ‘permissive use’ agreements allow some regular civil traffic to utilise the aerodrome facilities.

8.  In addition, civil charter operators frequently operate at other Defence airfields such as Richmond, Pearce and Amberley. Local agreements also exist with some commercial organisations to utilise Defence airfields from time to time for pilot training activities.

9.  ADFP 602 does not address issues such as runway surface conditions and will be replaced by the Defence Aerodrome Design Manual (DADM) in 2011. The DADM will in effect be a supplement to the MOS139 and will only detail Defence specific requirements that are not covered in MOS139 or where, due to operational requirements, MOS139 cannot be complied with. This Manual addresses the requirements of MOS 139, Section 10.15: Pavement Maintenance.

OBJECTIVES OF FRICTION TESTING

10.  The purpose of the ADF friction testing program is:

a.  To ascertain the current friction values on the runway surfaces.

b.  To compare these values to the relevant international standards.

c.  To assist Defence/Civilian Airport Operators in determining the necessity for rubber removal.

d.  Compliance with MOS 139.

Runway Surface Standards

11.  Section 6.2.9 of MOS 139 provides guidance on the required runway surface standards. This section states:

6.2.9.1 The surface of a bitumen seal, asphalt or concrete runway must not have irregularities that would result in the loss of frictional characteristics or otherwise adversely affect the take-off or landing of an aircraft.

6.2.9.1A The surface of a bitumen seal, asphalt or concrete runway must have an average surface texture depth of not less than 1mm over the full runway width and runway length.

Note: A runway surface meeting the ICAO minimum design objective for a new surface specified in Annex 14, Volume 1, derived using a continuous friction measuring device, is acceptable.

12.  If a runway surface cannot meet the above MOS139 requirements then a surface treatment must be provided. Acceptable surface treatments include grooving, porous friction courses or bituminous seals. Many airports provide grooving of the runway surface or have an open-graded surface to improve friction values. Townsville was the last Defence airfield to employ an open-graded friction course and was resurfaced with dense-graded asphalt and then grooved in 2006.

13.  A separate and supporting Defence policy is to groove asphalt runway surfaces where the runway is used by:

a.  RPT Jet Aircraft, and/or

b.  Military Jet Aircraft.

Importance of Adequate Runway Friction

14.  Aerodrome overrun and run-off incidents have been investigated by the Air Transport Safety Bureau (ATSB) in their safety report: Aviation Research and Analysis Report – AR-2008-018(2) final, titled: Runway excursions, Part 2 – Minimising the risks of runway excursion accidents. This report is available at:

http://www.atsb.gov.au/publications/2009/ar2008018_2.aspx

15.  Adequate runway friction is especially important to jet transport aircraft as their stopping performance is very much dependent on the available friction between the aircraft tyres and the runway surface. Furthermore, their landing and take-off speeds are very high and these aircraft are more susceptible to directional control problems when operating in conditions that have strong cross-winds. For military aircraft carrying ordnance, braking performance is critical.

16.  ICAO identifies three distinct purposes in their Airport Services Manual for maintaining adequate runway friction:

a.  Deceleration of the aircraft after landing or after an aborted take-off,

b.  Maintenance of directional control, and

c.  Wheel spin-up at touchdown.

17.  Runway friction is particularly significant at touchdown for the spin-up of the aircraft wheels to full rotational speed. This has a significant affect on the operation of anti-skid braking systems and also directional control. Other aircraft operating systems that reduce residual lift and increase aerodynamic drag are only triggered when adequate wheel spin-up has been achieved.

Factors that Affect Runway Friction

18.  There are many factors that affect the frictional characteristics of a runway including surface texture, drainage, the presence of water, a build-up of rubber (from aircraft tyres) in the touchdown zones, a general polishing of the aggregate with time, tyre tread loss and other general contaminants.

19.  Much of the available guidance on runway friction considers conditions more extreme than those commonly found in Australia including snow, slush and ice. However, intense monsoonal rainfall events in northern Australia present conditions that are favourable for aquaplaning.

20.  ‘Normal’ wet friction is a term used to describe the condition where the presence of water on a runway will reduce the available friction coefficient to a level below its dry condition. This occurs when there is only partial contact between the aircraft tyre and the pavement surface as the water cannot be completely displaced upon contact. Under slow speeds, there is more time for this water to be displaced but as the speed increases the contact time is reduced and friction coefficients on wet surfaces will tend to fall.

21.  Aircraft performance corrections are applied under slippery or wet conditions to compensate for the aircraft’s reduced stopping capability. These corrections are applied by either reducing the allowable take-off or landing mass or by increasing the required runway length. Drainage is extremely important, as is the surface micro/macrotexture. Adequate tyre tread patterns (grooved etc) on the aircraft can also reduce the likelihood of aquaplaning.

22.  The mechanism of aquaplaning will occur when there is a sufficient depth of water on the runway to preclude the water from being cleared from the tyre contact area in sufficient time to permit dry contact. ICAO Aerodrome Design Manual, Part 3 (Pavements), 2nd edition, Para 5.2.5.4, Tire/surface interface drainage (macrotexture) states:

Interface drainage is actually a dynamic process, i.e., is highly susceptible to the square of speed. Macrotexture is therefore particularly important for the provision of adequate friction in the high speed range.

Coefficient of Friction – Definition

23.  The coefficient of friction is defined by ICAO as the ratio of the tangential force needed to maintain uniform relative motion between contacting surfaces (aircraft tyres and the pavement surface) to the perpendicular force holding them in contact (distributed aircraft weight to the tyre area). This coefficient is usually denoted µ and can be considered a simple way of quantifying the relative slipperiness of different pavement surfaces.

Methods of Friction Testing

24.  A continuous friction measuring device can be used for measuring friction values for wet runways. ICAO and CASA accept a range of different measuring devices including but not limited to Mu-meter, Runway Friction Tester, Skiddometer, Surface Friction Tester (SAAB), Tatra Friction Tester, Griptester and Runway Analyser and Recorder. It is highly desirable to test the friction characteristics of a runway pavement surface at more than one speed and in both directions to obtain adequate information. It is widely acknowledged that Continuous Friction Measuring Equipment (CFME) has poor repeatability and can also have calibration problems.

25.  It is not possible to directly correlate aircraft speeds/friction relative to ‘vehicle & friction test-rig’ speeds/friction as stated in the Aerodrome Services Manual, Part 2 (Pavement Surface Condition), Chapter 3.1.3:

Present Technology cannot provide a direct and immediate correlation of runway surface friction measurements, taken with a friction measuring device, with aeroplane braking performance on wet runways

26.  However, it has been found acceptable to use CFME as an indirect measure of performance and to demonstrate if a surface has good or poor surface friction characteristics. It is also a valuable tool to assist in the management of runway friction and particularly with respect to assessing the need or otherwise for rubber removal in the touch down zones.

ADF Friction Testing FRQUENCY

27.  The FAA Advisory Circular provides recommendations for the frequency of friction testing based on the number of daily turbojet aircraft landings per runway end. Defence recognises that the intention of this “guidance material” is to provide airport operators who have not previously performed friction testing with an ‘indicative’ value.

28.  Table 2 lists the ADF establishments and the frequency of testing.

ADF Airfield / Notes / Frequency of Testing
Darwin / DIA
RWY 11/29
RWY 18/36 / Joint-user airfield with DIA
Overlay completed in Nov 07
11/12: Overlay planned / 1 year
5 years
Williamtown/NAL
RWY 12/30 / Permissive Use Lease by Newcastle Airport
Overlayed in mid-2005 / 1 year
Amberley
RWY 15/33
RWY 04/22 / Regular use by transport/cargo aircraft
Overlayed in 2006
11/12: Overlay planned / 1 year
1 year
Townsville / TAPL
RWY 01/19
RWY 07/25 / Joint-user airfield with TAPL
Overlayed in 2006
Overlayed in 2009 / 2 years
6 years
Richmond
RWY 10/28 / Regular use by transport/cargo aircraft
Overlayed in 2006 / 2 years
Edinburgh
RWY 18/36 / Regular use by Maritime/cargo aircraft
12/13: Overlay planned / 2 years
Pearce/Gin Gin
RWY 18L/36R
RWY 05/23
RWY 08/26 / Training base – predominantly turbo prop.
10/11: Overlay planned
14/15: Overlay planned
10/11: Overlay planned / 3 years
3 years
3 years
East Sale
RWY 04/22
RWY 09/27 / Services civilian/RPT traffic
12/13: Overlay planned
12/13: Overlay planned / 3 years
3 years
Tindal
RWY 14/32 / Permissive Use Lease with Katherine Town Council & RFDS medical Evacuation to Darwin
Runway overlayed Oct 09 – Feb10 / 3 years
Learmonth
RWY 18/36 / Permissive Use Lease with the Shire of Exmouth
14/15: Overlay planned / 5 years
Woomera
RWY 18/36 / Used by charters and other forces.
12/13: Overlay planned / 5 years
Albatross
RWYs 03/21 08/26 / Occasional jet aircraft.
Overlayed April 2011 / 5 years
Oakey
RWYs 14/32 05/23 / Occasional jet aircraft.
Overlayed May 2011 / 5 years

Table 2: ADF Establishments – Friction Testing Frequency

Note: Curtin, Scherger, Williams, SWBTA runways, Wyoming and Emergency Runways are not included due to low use, aircraft type and climatic factors.