Operational Risk Management in Runway Excursion … FINAL REPORT Part 1-547.pdf · facilitating...

Operational Risk Management in Runway Excursion (Runway Friction Maintenance)

K i r a n K u m a r A

I n t e r n

B e n g a l u r u

I n t e r n a t i o n a l A i r p o r t

K i r a n 5 4 b l u e @ g m a i l . c o m

This study addresses the application of risk

management on aviation field and presents the

factors of runway excursion. Although risk is

inevitable, it is believed that flight accidents can be

minimized by a well-organized risk management

system.

OPERATIONAL RISK MANAGEMENT

1 VISVESVARAYA TECHNOLOGICAL UNIVERSITY

BENGALURU INTERNATIONAL AIRPORT

Bengaluru International Airport (BIA), India's first Greenfield airport, has been envisioned as a

business and travel hub for South India. It is an international airport serving the city of Bengaluru.

The airport is located 4 km (2.5 mi) south of Devanahalli and is 40 km (25 mi) from the central

business district of Bengaluru (30 km (19 mi) from the Bengaluru City Railway Station) and covers

4,000 acres (1,600 ha).It replaced the HAL airport. For the financial year 2010-11, it was the fourth

busiest airport in the country in terms of overall passenger traffic of 11.59 million and fifth busiest in

terms of international passenger traffic.

The airport handled about 9.3 million passengers and had air traffic movements (ATM) of about 280

per day in the year 2009. The airport is expected to handle 17 million passengers in the year 2015.

The airport is host to 10 domestic airlines and 21 international airlines connecting the city to about 50

destinations across India and rest of the world.

Ownership

BIAL is a Public Limited Company under the Companies Act formed to build, own and operate the

Bengaluru International Airport. BIAL has been given rights by the Government of India to develop,

design, finance, operate and manage the airport for a period of 30 years from the date of

commencement of commercial flight operations. It also has an option to extend the right for an

additional 30 years. Private promoters hold a 74% (Siemens Projects Ventures 40%, GVK 29% and

Unique Zurich 5%) stake in BIAL while the government holds the remaining 26% (Karnataka State

Industrial Investment and Development Corporation 13% and Airport Authority of India 13%).

Certifications

In early 2010, BIAL received the ISO 14001:2004 certification, an official recognition of the airport

management’s constant efforts towards a greener airport and city. May 2010 saw BIAL receive ISO

27001 certification for Information Security Management System Standards.

Following a process lasting almost six months, BIAL has had its work processes certified to the

internationally recognized quality management system standard, ISO 9001: 2008. Bengaluru

International Airport is now one of the first airports in the country to achieve this version of

ISO 9001

Apart from the certification received, BIAL has received many esteemed awards.

40%

29% 5%

13% 13%

Percentage Ownernship

Seimens Projects Ventures

GVK

Unique Zurich

KSIDC

AAI



ACKNOWLEDGEMENT

The satisfaction and euphoria that accompanies the successful completion of any task would

be incomplete without the mention of the people who made it possible, whose constant

guidance and encouragement crowned out efforts with success.

It is with immense gratitude and pride that I wish to thank Bengaluru International Airport

(p) Ltd,(BIAL) for providing a unique learning opportunity and corporate exposure by

facilitating internship in this prestigious project and express my sincere gratefulness to Mr.

Hari kumar P, Vice President- Engineering and Maintenance Department, for providing

valuable support throughout the internship.

I am thankful to Mr. Dinesh, Deputy General Manager & HEAD, Air field, BIAL, Mr.

Saroj jha, Maintenance Manager, Air field Civil, BIAL.

I also thank individually the Management and staff of AIR SIDE CIVIL for the excellent

co-operation and facilities extended, enabling me to complete the internship.

Special thanks to Mr. Manjunath, HR Manager, BIAL, Mr. Appala Raju Nagireddy,

Deputy Manager, Plant Maintenance, Mr. Sasi Kumar, Ware House controller,

Infrastructure, BIAL.

I take this opportunity to thank Prof. B. Bhaskara Rao, Executive Director, MINDS, my

guide Prof. V.M. Hegde and all other professors and staff of MINDS for enabling course and

providing me support and guidance.

I am thankful to my Parents and friends who guided me in completion of project in many

ways.



TABLE OF CONTENTS

1. Introduction 4-7

2. Literature Review 8-21

Mechanics of Tyre Pavement Friction 8-12

Pavement 12-15

Tyre 15-17

Miscellaneous Factors 17-21

3. Operational Risk Management (ORM) 22-27

Risk and Risk Management 22-23

ORM Principle 23-24

Types of Risk 24

General Risk Management Guidelines 25

Risk Management Responsibilities 25-26

5M-Model 26-27

4. ORM in Runway Excursion (Friction Maintenance) 28-58

Hazard Identification 28-38

Analyse Control Measures 39-53

Supervise & Review 54-58

5. Conclusion 59

6. References 60



1. INTRODUCTION

Today’s busy international airports handle ever increasing levels of traffic and the turnaround

times for aircraft are becoming ever shorter. Modern airport runways have to be capable of

safely landing turbojet aircraft with their greater weight and high landing speeds.

An average landing leaves as much as 1.4 lb (700 g) of rubber in a thin layer on the runway.

To make matters worse, the heat generated during the interaction causes a chemical reaction

called polymerization that changes the rubber deposits into a hard, smooth material. This

buildup of rubber fills the micro-and macrotexture of the pavement, causing a serious loss of

skid resistance, nothing but friction deterioration.

Fig 1.1: Landing of aircraft tyres which generates around 3000

celsius

Fig 1.2



Friction Deterioration

The skid-resistance of runway pavement deteriorates due to a number of factors, the

primary once being mechanical wear and polishing from aircraft tyres rolling or

braking on the pavement.

Accumulation of contaminants, mostly rubber, but also dust particles, jet fuel, oil

spillage, water, snow, ice, and slush, all cause friction loss on runway pavement

surfaces.

The most persistent contaminant problem is deposits of rubber from tyres of landing

jet aircraft.

Rubber deposits occur at the touchdown, take-off and high speed exit areas on

runways.

.

4400mkjkjk

Fig 1.3: Primary rubber deposition area

The effect of these factors is directly dependent upon the volume and type of aircraft

traffic



Fig: 1.4 Rubber depositions are absolutely dangerous if runway surface is wet

The most significant reason to be concerned about the buildup of rubber deposits is SAFETY.

If you operate an airport with large jet aircraft, you will eventually have a deterioration of the

pavement skid‐resistance, or a reduction in friction coefficients, which is a problem for

aircraft tyres to grab and safely stop the aircraft. One of the main causes of ground based

accidents is a runoff event. When an aircraft skids off of the runway, whether the pilot is

unable to brake soon enough upon landing or when having to abort a takeoff, the pavement

surface will be carefully examined as a contributing factor. There are several factors that

contribute to surface deterioration, but the one that is easy to recognize, simple to correct and

relatively inexpensive to do is AIRFIELD RUBBER REMOVAL.



OBJECTIVE:

This study addresses the application of risk management on aviation field and presents the

factors of runway excursion. Although risk is inevitable, it is believed that flight accidents

can be minimized by a well-organized risk management system.

The study involves the following process:

1. Risk identification

Task(rubber removal on the Runway)

List hazards (damages occurred )

List causes for rubber deposition on the Runway

2. Analyse control measures

Identify control options for Rubber removal

Determine control effects of each of them

Prioritize risk control measures

Implement risk control

3. Review



2. LITERATURE REVIEW

TYRE-PAVEMENT FRICTION

2.1 MECHANICS OF TYRE-PAVEMENT FRICTION:

The mechanics of tyre-pavement friction are fundamental to any study of the runway rubber

process. In this section the history and two main components of friction are reviewed.

2.1.1 HISTORY: In ancient times the Egyptians, Greeks and Romans knew about friction

and were aware of the need for lubricants. During the Renaissance, approximately 1508,

Leonardo da Vinci considered friction in his writings and speculated that friction is

proportional to load. In more modern times Guillaume Amontons first proposed the two main

laws of friction. In 1699, Amontons suggested that friction force is proportional to normal

force and that friction is independent of the size of the bodies in contact. Amontons also

attributed the cause of friction to surface roughness. That is, he saw frictional resistance as

the force required to lift one rigid surface over the asperities of another surface. In 1724 Jean

Theophile Desaguliers observed that adhesion is a component of friction. Then in

approximately 1779, Charles Augustine Coulomb began to investigate friction.

In his 1781 paper, Theory of Simple Machines, Coulomb determined that the following

parameters were important in friction: "nature of materials in contact and their coating; the

surface area, the normal force, time of repose, relative velocity". Coulomb considered the

work of Desaguliers on adhesion but rejected the idea. He felt friction developed from a

surface lifting over asperities, and the asperities bending and breaking, he considered surface

cohesion a negligible factor. Samuel Vince, in 1785, rejected the notion that friction is

proportional to load and said friction does, to some extent, depend on the size of the bodies in

contact. Vince defended surface cohesion as a factor in friction. In 1804, John Leslie took a

negative attitude toward adhesion while trying to explain the energy loss in friction. Further

developing on the surface asperity theory, Leslie said friction arises from deformation losses

in the sliding interface of two bodies, this is now called "ploughing effect, plastic

displacement or, in the case of elastic solids, hysteresis losses." The debate over the

proportions, or even existence, of adhesion and hysteresis components in surface friction

continued. Ewing (1892), Hardy (1936), and Tomlinson (1929) were influential proponents

of adhesion, while Bikerman defended the views of Coulomb. Bowden and Tabor (1954), and

many others since, agree that both adhesion and hysteresis components of friction do exist. In

the area of tyre-pavement friction, there has been interest since the late nineteenth century.



Researchers recognized that the coefficient of friction was greater when sliding was

impending versus during sliding. In the 1920's, T.R. Agg performed research on pavement

slipperiness at Iowa State College. Agg sprayed water on the ground, then pulled a locked-

wheel car outfitted with a mechanical recorder, over the wet ground. From his tests, Agg

determined that, "the coefficient of friction as measured in these investigations (in the field)

is apparently the factor the engineer must deal with in problems of design”. With the

proliferation of the automobile and expansion of the road network came an increased

awareness of the need for adequate tyre-pavement friction. In 1958, the first international

skid prevention conference was held. And in 1959, the American Society for Testing and

Materials (ASTM) established Committee to investigate skid resistance.

While automobile traction was gaining attention, aircraft traction was not being ignored. The

National Aeronautics and Space Administration (NASA) took the lead in studying aircraft

tyre-pavement friction. In 1954, NASA put the Langley landing-loads truck into operation to

simulate aircraft landing on runways. In 1956, the initial hydroplaning studies were

performed. Interest in aircraft skid resistance was boosted by the introduction of heavier,

faster commercial jet aircraft in the late '50's. Some of the achievements in aircraft tyre-

pavement research are listed below:

1960 NASA began research on aircraft braking performance on dry and wet runway

pavements of various textural and groove configurations.

1965-67 Correlation between profile tracing devices/outflow meter/sand patch test (surface

texture measurement methods) and skid resistance gradient established.

1967 Landing research runway completed at NASA Wallops Station.

1968 Pavement grooving studied by NASA. NASA, Federal Aviation Administration (FAA),

and British Ministry of Technology attempted to relate the test results of various friction

measuring devices to actual aircraft braking performance, thereby allowing establishment of a

standard critical value below which measured friction should not fall.

1970 Modified sand patch test found to have poor repeatability and poor correlation with skid

resistance



1972 Part 139 of the Federal Aviation Regulations (FAR), adopted. In part, this required

certificate holders to remove airfield pavement contaminants (including rubber) as promptly

and as completely as practicable.

1978-80 FAA conducted friction and pavement evaluation surveys at 268 airports (491

runways) within the contiguous United States

1982-85 FAA conducted a series of tests and found the Mu-Meter, Saab Friction Tester;

Skiddometer, and Runway Friction Tester all reliable; FAA also established correlation

values between the four devices.

1983 FAA Technical Centre study determined the optimum groove dimensions.

1983-86 NASA study correlated friction measuring devices and aircraft braking action on ice

and snow-covered runways.

Tyre-pavement friction like friction in general, has been the subject of some disagreement.

The interaction of a viscoelastic material tyre with a relatively rigid pavement surface does

not accord with the classical laws of friction. Most now feel that adhesion is the greater of the

two main components of surface friction. However, there are still some who contend, with

Coulomb, that adhesional forces are negligible and that hysteresis forces predominate in

surface friction - especially when rolling viscoelastic materials are involved.

2.1.2 ADHESION AND HYSTERESIS:

A pavement surface may appear smooth, when it is actually characterized by undulations and

asperities. As a rubber, or elastomer, surface passes over the pavement, the elastomer drapes

over the pavement asperities (see Figure 1).

The area of contact between elastomer and asperities is proportional to the normal force. "If a

force F is now applied tangentially to the upper surface, relative motion at the frictional

interface takes the form of a 'flowing' action as the elastomer conforms to the asperities of the

base. A frictional force equal in magnitude and opposite in direction to the applied force F is

generated at the sliding interface, and it includes both adhesional and hysteresis components,

thus: F=F(adh)+F(hys).



Figure 1: Principal Components of Elastomeric Friction

Adhesion occurs at the contact points because molecules on the opposite surfaces "are so

close together that they exert strong intermolecular forces on each other". In effect, the

molecules on opposite surfaces bond. As a tyre rolls, the bonds are stretched and broken.

Thus a “dissipative stick-slip" molecular process is fundamentally responsible for adhesional

friction. The physical laws governing this phenomenon have yet to be discovered .Another

name for the hysteresis component of tyre pavement friction is bulk internal friction.



As an elastomer moves relative to the pavement asperities, it tends to "'accumulate' or 'pile

up' at the leading edge of the asperity and to break contact at a higher point on the downward

slope". An unsymmetrical pressure distribution results (see Figure 1) where the horizontal

pressure components oppose the sliding motion. Energy is dissipated within the rubber bulk

due to stress relaxation. Theoretically, on a clean, dry plate glass surface with no

deformations, F=F(adh). On a well-lubricated irregular surface, where the lubricant makes

shear strength of the contact area trivial, F=F(hys). Many other complicating factors cloud the

investigation of tyre-pavement friction. Analysis in sterile laboratories cannot duplicate the

myriad interacting effects on tyre pavement friction of pavement, tyres, drainage, aircraft

characteristics, pilot techniques, climate, and contaminants. Further investigation is needed to

fully understand the mechanics of aircraft rolling tyre-pavement friction.

2.2 PAVEMENT:

Fundamental to tyre-pavement friction is the texture of the pavement. Other pavement

characteristics will also induce changes in the achievable amount of surface friction.

2.2.1 TEXTURE:

Pavement textures may appear smooth, but actually are characterized by undulations and

asperities. The texture can be broken into two sub-groups; macrotexture, or macro-roughness,

and microtexture, or micro-roughness (see Figure 2).

2.2.1.1 MACROTEXTURE: Macrotexture is the visible "surface relief of the pavement".

On an asphalt pavement this is the aggregate, while on a portland cement concrete pavement

it is the surface finish. By definition, macrotexture has a wavelength and amplitude of 0.5

mm or more. The main function of the macrotexture is to permit the escape of water from

under the tyre. Fig: 2



2.2.1.2 MICROTEXTURE: Microtexture refers to "the finescale roughness contributed by

small individual asperities of aggregate particles on pavement surfaces which are not

discernible to the eye but are apparent to the touch". Microtexture largely affects the adhesion

component of tyre-pavement friction. On a wet pavement the microtexture penetrates a thin

layer of water, allowing adhesion between the tyre and pavement.

2.2.2 OTHER PAVEMENT CHARACTERISTICS:

Several factors influence a pavement's macro- or micro-texture. Pavement type, construction

techniques, condition. and drainability all play a role in tyre-pavement friction. Runway

pavements are normally constructed of portland cement concrete (PCC) or asphalt concrete

(AC). Grooves or a porous friction course (PFC) are sometimes added to the pavement

structure to assist the macrotexture in water drainage.

2.2.2.1 PORTLAND CEMENT CONCRETE (PCC) PAVEMENT:

In a PCC pavement, macrotexture is developed by texturing in "ridges of fine mortar and

aggregate". The FAA recommends fine aggregate (sand) and an average texture depth of

0.025 inches (0.25 mm) to provide an adequate friction surface. If the pavement macrotexture

is low, water may build up at the tyre-pavement interface, obscuring the microtexture and

decreasing tyre-pavement friction. During construction, while the concrete is still in a plastic

condition, texture can be constructed into the PCC pavement by finishing with a natural-

bristle paving broom, heavy burlap drag, wire brushes, wire combing, or a fluted magnesium

float.

The best time to texture a PCC pavement is during construction, "when the water spots have

dried enough to hold the texture but before the drier spots have dried too much to texture".

Immediately after texturing, "application of the curing compound assures that the pavement

surface will not lose water and cure too rapidly". If the surface dries too quickly, mortar

ridges will not set up properly leading to reduced durability and faster loss of skid resistance.



2.2.2.2 ASPHALT CONCRETE (AC) PAVEMENT:

In an AC pavement, the coarse and fine aggregate create an illusion of adequate macro- and

micro-texture. In truth, "due to the 'smoothing' effect of rolling equipment, the coarse

aggregate rarely penetrate above a thin film of water". Given normal quality control methods

are used, there is not much that can be done during construction to improve AC surface

friction. In design, soft aggregate and excessive binder should be avoided. Excess binder may

cause the pavement to bleed, coating the microtexture and thereby reducing tyre-pavement

friction. Soft aggregate will polish, that is the microtexture will be worn off, again reducing

tyre-pavement friction. The FAA recommends large, angular aggregate such as unweathered,

crushed quartzite, quartz diorite, granodorite, and granite-rocks high in silica (versus

aggregate high in carbonate).

The "presence of coarse grain sizes and gross differences in grain hardness appear to combine

and lead to differential wear and breaking off of grains" leading to a constantly renewed

abrasive surface. Various methods are available for providing and restoring macrotexture in

AC pavements. Possibilities include: chip seals, aggregate slurry seals, cold milling, Porous

Friction Course (PFC) overlays, and grooving.

2.2.2.3 DRAINAGE:

Increasing a pavement's drainage capability means a dryer tyre-pavement interface and

increased surface friction. The FAA recommends a transverse slope on runways of at least

1.5% for effective drainage. PFC overlays and grooving are two common airport techniques

for increasing a pavement's drainability. The advantage of these two techniques is that, in

themselves, they increase the pavement macrotexture in addition to accentuating microtexture

through improved water runoff.

2.2.2.3.1 POROUS FRICTION COURSE (PFC) OVERLAY:

PFC overlay is a thin asphaltic overlay - usually 1-1.5 inches (25-38 mm) thick. The

pavement is made porous by increasing the percent of voids and using a high proportion of

uniform-sized aggregate with little filler or binder. On a porous overlays water that does not

run off will flow through the surface and drain off transversely allowing the tyres to interface

with the pavement microtexture. The FAA does not recommend PFC overlays for runways

with greater than 450 aircraft operations per day. Rubber deposits and contaminants can

accumulate in pavement voids, significantly reducing the overlay's drainage capability.



2.2.2.3.2 GROOVING:

It is common at airfields to transversely groove the runway surface. Initially, grooved

pavements were responsible for chevron-type cuts and chipping in tyres. Adjustments in

aircraft tyre design were made to eliminate this type of tyre distress. In fact, now it is reported

that "grooved pavements accumulate less rubber for a given amount of usage than ungrooved

pavements". Grooved pavements remove bulk water from the runway, thereby allowing the

pavement macro- and micro-texture to interface with aircraft tyres. An after effect of grooves

is, in themselves, an increased macrotexture. Both NASA and FAA studies showed a high

level of friction was maintained by using 0.25" x 0.25" (6 mm x 6 mm) grooves, 1.5" (38mm)

apart, this is now the standard FAA configuration. The FAA has found that grooves need not

extend to the runway edge to be effective.

2.3 TYRES:

Diverse elements play a role in the tyre portion of tyre-pavement friction. Tyre material,

tread pattern, type, pressure, and wear/aging are the primary constituents.

2.3.1 MATERIAL: Some properties of five common synthetic rubbers used in tyre

construction are depicted in Figure 3. By altering the tyre material mix, manufacturers can

greatly influence tyre-pavement friction. Peterson et. al.,for example, found that vehicles with

a BR-type rubber tyre required 180 feet to stop (on a wet asphalt road), while a butyl-type

rubber tyre stopped within 130 feet. They found that "a softer rubber will be deformed more

by a given asperity, and a high-hystersis rubber will be capable of absorbing a greater

percentage of the energy produced in such deformations". In other words tyres with soft,

high-hystersis rubber will improve traction.



TYPE OF SYNTHETIC

RUBBER

ABBREVIATION PROPERTIES

NEOPRENE

CR

High tensile strength

Good resistance to ageing and weathering

Poor bonding to carcass fabrics

STYRENE-

BUTADIENE

SBR

Excellent abrasion resistance

High hysteresis

Good resistance to cracking

Strong bonding to carcass

Poor tear and cutting resistance

POLYBUTADIENE

PB or BR

Very stable over wide temperature range

Good wear resistance

Strong tear and cutting resistance

Poor wet traction

BUTYL

IIR

Low gas permeability

High hysteresis

Good traction characteristic

Poor affinity for blending

POLYISOPRENE

PI

Strong wear resistance

Very similar to natural rubber

Low sensitivity to heat build-up

Figure 3 Some Properties of Synthetic Rubber Materials

2.3.2 TREAD PATTERN:

Tread pattern plays an important role in tyre-pavement friction when pavements are

lubricated. When a pavement is dry, the best tread pattern is no tread design at all, that is, the

greatest amount of surface contact possible is desired. When a pavement is lubricated, the

tyre tread pattern acts to, remove the lubricant, thus enabling tyre-pavement contact/friction.

The variety of automobile tread patterns promoted to increase tyre-pavement friction is nearly

innumerable. Aircraft tyres, on the other hand, usually utilize a simple longitudinal rib

pattern.



2.3.3 PRESSURE:

Tyre pressure is a delicate issue when it comes to tyre-pavement friction. Increased tyre

pressure shrinks the tyre-pavement contact area and allows water to escape easier. A higher

tyre-pavement pressure also discourages entrapped water at the tyre-pavement interface. In

wet conditions, this permits greater traction. Conversely, in dry conditions, decreased tyre

pressure increases the tyre-pavement contact area and, therefore, tyre-pavement friction.

Aircraft personnel are more concerned about traction in wet conditions, and as a result

aircraft tyres are designed for high tyre pressures.

2.3.4 WEAR/AGING:

Tyre wear/aging is affected by the manufacturer, user, and environment. Manufacturers can

alter tyre materials to increase wear resistance. Users can prolong tyre life by diligent

maintenance, proper pressure, balance, alignment, and timely retreads. If the user lets his

tyres wear unevenly or excessively, the tyre tread pattern will be ineffective in removing

lubricants, tyre pavement contact area will be reduced, and available friction will be lowered.

Pavement surface defects, chemicals, and the sun all may work together to prematurely age a

tyre.

2.4 MISCELLANEOUS FACTORS:

Items which affect tyre pavement friction are legion. This section investigates some of these

factors, including: contaminants, speed, temperature, and seasons.

2.4.1 CONTAMINANTS: As noted in earlier sections, adhesion is a very important

component of tyre-pavement friction. Since adhesion is largely controlled by a pavements

microtexture, anything that diminishes a pavement's microtexture will reduce tyre-pavement

friction and create unsafe conditions. Contaminants such as water, snow, ice, slush, dusts

sand, mud, organic debris, fuel, oil, grease, chemicals, and rubber deposits may lodge in/over

the pavement asperities, obscure the micrcotexture, and act as a crude lubricant to prevent

tyre-pavement friction.



2.4.1.1 WATER: When a tyre travels over a wet pavement at high speeds, the tyre-pavement

contact is reduced. Water is unable to quickly escape from under the moving tyre and an

incompressible wedge forms, lifting the tyre from the pavement (see Figure 4).

Figure 4 Contact Areas between Tyre and Road Surface

If the tyre tread, pavement macrotexture, and slope do not remove enough water from the

tyre-pavement interface, friction will be nil and dynamic hydroplaning will occur. Also

possible are viscous hydroplaning (where a "thin film of fluid remains between tyre and

pavement since there is insufficient pavement microtexture to promote its breakdown") and

tyre tread reversion skidding (which “occurs at high speeds on wet pavement with macro but

little microtexture, heat build-up due to sliding causes rubber to revert and melt, slides along

on cushion of molten rubber, water and steam") See Figure 5.

Figure 5: Causes of Wet Pavement Tyre Friction Losses



2.4.1.2 RUBBER DEPOSITS: When aircraft tyres impact a runway pavement, "a certain

amount of rubber is transferred from the tyre to the pavement as a result of heat and abrasion

produced when the aircraft tyres spin-up". Rubber "first coats the finer microtexture, then

occludes the macrotexture as rubber build-up increases". Rubber coating the microtexture

changes sharp asperities to rounded spheres which cannot generate the hydraulic pressure

necessary to penetrate the thin viscous films of water on a wet runway. Thus dry tyre-

pavement contact and, therefore, adhesion are constrained. If rubber continues to increase

until the macrotexture is occluded, bulk water drainage is impeded and hydroplaning is

further encouraged. When tyres go from rotating at zero velocity to rotating at touchdown

velocity, immediately following touchdown, it is known as "spin-up". In aircraft brake

design, braking efficiency is reduced if tyres do not move at the same velocity as the aircraft.

When aircraft tyres are unable to fully spin-up due to insufficient friction, then aircraft

braking is impaired and safety becomes a key concern. Among other things, rubber accretion

is a function of the number of aircraft landings. MacLennan, et.al, found that "runways with

landings less than 250 million pounds (aircraft landing weight) per year rarely have

significant rubber accumulation" and of runways with no record of rubber removal, very few

had landings with greater than 5,000 million pounds per year.

2.4.2 SPEED: In tyre-pavement friction,"microtexture provides frictional properties for

aircraft operating at low speeds and macrotexture provides frictional properties for aircraft

operating at high speeds”.

Fig: 6



Figure 6 graphically portrays the relationship of velocity to the adhesion (fA) and hysteresis

(fH) components of tyrepavement friction. Small general aviation aircraft are able to exit

runways more quickly because their slower landing speeds allow greater initial tyre-

pavement friction. Modern jet aircraft, with their higher operational speeds and heavier gross

weights, require high shear forces generated at the tyre-pavement interface for safe operation.

A quick glance at Figure 6 shows the limited amount of friction available to high speed

aircraft in favorable conditions, safely stopping an aircraft on a short, wet, and windy runway

can be a problem. Light jet aircraft (business jets, military fighter planes) especially find it

difficult to taxi off such a runway over slick rubber deposits.

2.4.3 TEMPERATURE:

Tyre, pavement and water temperatures all play a role in tyre-pavement friction. High

ambient temperatures warm tyres, pavement, and water. The increase in molecular motion at

the tyre-pavement interface induces a drop in both the adhesion (fA) and hysteresis (fH)

components of tyre-pavement friction (see Figure 7). This drop is chiefly due to the inverse

relationship of adhesion and hysteresis to the amount of energy stored in a tyre. Moore says,

"Both the tensile strength of natural rubber and cord/rubber adhesion" decrease with

increasing temperature. Thus, theoretically, when higher ambient, pavement and water

temperatures increase a tyre's internal temperature, tyre-pavement friction is reduced.

Pavement and water temperature significantly impact surface friction.

MacLennan, et. al., found variations as high as 8 Mu Numbers (MuN - refers to the

coefficient of friction as measured by a Mu-Meter) on the same surface, depending on the

pavement and water temperature. Specifically, they found that friction decreases with

increasing water temperature at a rate of 0.5 MuN per degree C. Surprisingly they reported

friction increases with increasing pavement temperature at a rate of 0.2 MuN per degree.

Fig : 7



2.4.4 SEASONS:

Tyre-pavement friction fluctuates with the seasons. As measured by skid number, tyre-

pavement friction is generally at a maximum in late winter/early spring and at a minimum in

late summer. There are several reasons for this trend. In summer, dust and other contaminants

inhibit tyre-pavement adhesion. In winter, rains wash contaminants from the pavement. And,

as an observation, rubber is not deposited as readily on wet pavements and snow removal

equipment, used at northern climate airports, partially scrapes off rubber deposits.



3. Operational Risk Management (ORM)

3.1 Defining Risk and Risk Management

ORM is a decision-making tool to systematically help identify operational risks and benefits

and determine the best courses of action for any given situation. In contrast to an Operational

and Support Hazard Analysis (O&SHA), which is performed during development, ORM is

performed during operational use. For example, an ORM might be performed before each

flight. This risk management process, as other safety risk management processes is designed

to minimize risks in order to reduce mishaps, preserve assets, and safeguard the health and

welfare.

The approach is based on the philosophy that it is irresponsible and wasteful to wait for an

accident to happen, then figuring out how to prevent it from happening again. We manage

risk whenever we modify the way we do something to make our chances of success as great

as possible, while making our chances of failure, injury or loss as small as possible. It’s a

common sense approach to balancing the risks against the benefits to be gained in a situation

and then choosing the most effective course of action.

Often, the approach to risk management is highly dependent on individual methods and

experience levels and is usually highly reactive. It is natural to focus on those hazards that

have caused problems in the past. In the operational environment where there is a continual

chance of something going wrong, it helps to have a well-defined process for looking at tasks

to prevent problems. Operational Risk Management, or ORM, is a decision-making tool that

helps to systematically identify risks and benefits and determine the best courses of action for

any given situation. ORM is designed to minimize risks in order to reduce mishaps, preserve

assets, and safeguard the health and welfare.

Risk is defined as the probability and severity of accident or loss from exposure to various

hazards, including injury to people and loss of resources. All operations indeed even our

personal daily activities involve risk, and require decisions that include risk assessment and

risk management. Operational Risk Management (ORM) is simply a formalized way of

thinking about these things. ORM is a simple six-step process, which identifies operational

hazards and takes reasonable measures to reduce risk to personnel, equipment and the

mission.



In operations, decisions need to take into account the significance of the operation, the

timeliness of the decision required, and what level of management is empowered to make the

decision. Risk should be identified and managed using the same disciplined process that

governs other aspects of the Agency’s endeavors, with the aim of reducing risk to personnel

and resources to the lowest practical level.

Risk management must be a fully integrated part of planning and executing any operation,

routinely applied by management, not a way of reacting when some unforeseen problem

occurs. Careful determination of risks, along with analysis and control of the hazards they

create results in a plan of action that anticipates difficulties that might arise under varying

conditions, and predetermines ways of dealing with these difficulties. Managers are

responsible for the routine use of risk management at every level of activity, starting with the

planning of that activity and continuing through its completion.

3.2 ORM Principles

Four principles govern all actions associated with operational risk management. These

continuously employed principles are applicable before, during and after all tasks and

operations, by individuals at all levels of responsibility.

Accept No Unnecessary Risk:

Unnecessary risk is that which carries no commensurate return in terms of benefits or

opportunities. Everything involves risk. The most logical choices for accomplishing an

operation are those that meet all requirements with the minimum acceptable risk. The

corollary to this axiom is “accept necessary risk,” required to successfully complete the

operation or task.

Make Risk Decisions at the Appropriate Level:

Anyone can make a risk decision. However, the appropriate decision-maker is the person

who can allocate the resources to reduce or eliminate the risk and implement controls. The

decision-maker must be authorized to accept levels of risk typical of the planned operation

(i.e., loss of operational effectiveness, normal wear and tear on materiel). He should elevate

decisions to the next level in the chain of management upon determining that those controls

available to him will not reduce residual risk to an acceptable level.



Accept Risk When Benefits Outweigh the Costs:

All identified benefits should be compared against all identified costs. Even high-risk

endeavors may be undertaken when there is clear knowledge that the sum of the benefits

exceeds the sum of the costs. Balancing costs and benefits is a subjective process, and

ultimately the balance may have to be arbitrarily determined by the appropriate decision-

maker.

Integrate ORM into Planning at all Levels:

Risks are more easily assessed and managed in the planning stages of an operation. The later

changes are made in the process of planning and executing an operation, the more expensive

and time-consuming they will become.

3.3 Types of Risk Defined

Identified risk: That risk that has been determined to exist using analytical tools. The time

and costs of analysis efforts, the quality of the risk management program, and the state of the

technology involved affect the amount of risk that can be identified.

Unidentified risk: That risk that has not yet been identified. Some risk is not identifiable or

measurable, but is no less important for that. Mishap investigations may reveal some

previously unidentified risks.

Total risk: The sum of identified and unidentified risk. Ideally, identified risk will comprise

the larger proportion of the two.

Acceptable risk: The part of identified risk that is allowed to persist after controls are

applied. Risk can be determined acceptable when further efforts to reduce it would cause

degradation of the probability of success of the operation, or when a point of diminishing

returns has been reached.

Unacceptable risk: That portion of identified risk that cannot be tolerated, but must be either

eliminated or controlled.

Residual risk: The portion of total risk that remains after management efforts have been

employed. Residual risk comprises acceptable risk and unidentified risk.



3.4 General Risk Management Guidelines

All human activity involving technical devices or complex processes entails some

element of risk.

Hazards can be controlled; they are not a cause for panic.

Problems should be kept in perspective.

Judgments should be based upon knowledge, experience and mission requirements.

Encouraging all participants in an operation to adopt risk management principles both

reduces risk and makes the task of reducing it easier.

Good analysis tilts the odds in favor of safe and successful operation.

Hazard analysis and risk assessment do not replace good judgment: they improve it.

Establishing clear objectives and parameters in risk management works better than

using a cookbook approach.

No one best solution may exist. Normally, there are a variety of alternatives, each of

which may produce a different degree of risk reduction.

Tact is essential. It is more productive to show a mission planner how he can better

manage risk than to condemn his approach as unworkable, risky, unsafe or unsound.

Seldom can complete safety be achieved.

There are no “safety problems” in planning or design, only management problems

that may cause accidents, if left unresolved.

3.5 Risk Management Responsibilities

Managers

Are responsible for effective management of risk.

Select from risk reduction options recommended by staff.

Accept or reject risk based upon the benefit to be derived.

Train and motivate personnel to use risk management techniques.

Elevate decisions to a higher level when it is appropriate.



Staff

Assess risks and develop risk reduction alternatives.

Integrate risk controls into plans and orders.

Identify unnecessary risk controls

Supervisors

Apply the risk management process

Consistently apply effective risk management concepts and methods to operations

and tasks.

Elevate risk issues beyond their control or authority to superiors for resolution.

Individuals

Understand, accept and implement risk management processes.

Maintain a constant awareness of the changing risks associated with the operation or

task.

Make supervisors immediately aware of any unrealistic risk reduction measures or

high-risk procedures.

3.6 Systematic Risk Management: The 5-M Model

Successful operations do not just happen; they are indicators of how well a system is

functioning. The basic cause factors for accidents fall into the same categories as the

contributors to successful operations—Human, Media, Machine, Mission, and Management.

Risk management is the systematic application of management and engineering principles,

criteria and tools to optimize all aspects of safety within the constraints of operational

effectiveness, time, and cost throughout all operational phases. To apply the systematic risk

management process, the composite of hardware, procedures, and people that accomplish the

objective, must be viewed as a system

The 5-M model, depicted in Figure 3.1, is adapted from military ORM. In this model, “Man”

is used to indicate the human participation in the activity, irrespective of the gender of the

human involved. “Mission” is the military term that corresponds to what we in civil aviation

call “operation.” This model provides a framework for analysing systems and determining the

relationships between the elements that work together to perform the task.



The 5-M's are Man, Machine, Media, Management, and Mission. Man, Machine, and Media

interact to produce a successful Mission (or, sometimes, an unsuccessful one). The amount of

overlap or interaction between the individual components is a characteristic of each system

and evolves as the system develops. Management provides the procedures and rules

governing the interactions between the other elements. When an operation is unsuccessful or

an accident occurs, the system must be analysed, the inputs and interaction among the 5-Ms

must be thoroughly reassessed. Management is often the controlling factor in operational

success or failure. The National Safety Council cites the management processes in as many as

80 percent of reported accidents.

5M model of System Engineering

Fig: 3.1

• Msn - Mission: central purpose or functions

• Man - Human element

• Mach - Machine: hardware and software

• Media - Environment: ambient and operational environment

• Mgt- Management: procedures, policies, and regulations

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