ce-461 ce-461 taxiway geometric design(1)

7/24/2019 CE-461 CE-461 Taxiway Geometric Design(1)

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Transportation Engineering - II

Taxiway Geometric Design

Dr. Indrajit Ghosh

Assistant Professor

Department of Civil Engineering

Indian Institute of Technology Roorkee


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Lecture Outline

Taxiway Requirements

Length, Width of Taxiway

Transverse and Longitudinal Grade Sight Distance

Design of Turning Radius

Separation Distance


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Taxiway

Paths on airport surface for taxiing of aircraft

Intended to provide linkage between one part ofairport and another

Aircraft movement on taxiways are essentiallyground movements

Relatively slow


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Taxiway

Factors controlling layout

Minimum interference between just-landed aircraft

and ready to take-off aircraft

At busy airports, provision of taxiways at variouslocations along runway to assist landing aircrafts

leave and clear runway ASAP

Exit taxiway

Facilitate aircrafts leave runway at higher speeds

Reduce runway occupancy time and increase airport

capacity


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Taxiway

Factors controlling layout

Avoid intersection of taxiway and active runway

Shortest possible distance between terminal

building/apron and end of take-off runway


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Length

Width of taxiway

Width of shoulder

Transverse gradient

Longitudinal gradient

Rate of change of longitudinal gradient

Sight distance Turning radius

Separation clearance


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Length

No specifications has been suggested by any

organization

Should be as short as possible

Saves fuel


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Width of taxiway

Lesser than runway

Aircraft is not airborne

Speeds are lower

There is not much variability in maneuverability of

aircraft

Nose of aircraft follows taxiway centerline Standard need not be so rigorous as in case of runway

Varies between 7.5 m and 23 m


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Width of taxiway (ICAO)

Airport Code Taxiway width

A 7.5 m

B 10.5 m

C 15 m {if taxiway is used by aircraft with

a wheel base less than 18 m}

D 18 m {if used by aircraft with an outer

main gear wheel span of less than 9 m,otherwise 23 m)

E 23 m


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TaxiwayGeometric

Width of shoulder

Should extend beyond pavement of taxiway on

either side

Ordinary aircrafts (before advent of jets)

Shoulders were of ordinary soil protected by low

growing vegetations

Sometimes stabilized soil was used to preventerosion of shoulder material due to high speed of

propellers


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Width of shoulder

Jet aircrafts

Hot blasts coming out at high speed needs a paved

surface on shoulder

A bituminous pavement which provides an

impervious, smooth and resistant shoulder is

provided up to 7.5 m adjacent to taxiway edge


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TaxiwayGeometric

Transverse gradient

Required for quick disposal of rain water

Adopted same as recommended for runways

ICAO recommended maximum pavementtransverse gradients of 2 percent for A and B

1.5 percent for airports with code C, D and E type ofairport

No min. value is specified Min. gradient is taken as 0.5 percent for rigid pavement case

and 1 percent for other cases

For drainage


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TaxiwayGeometric

Transverse gradient

ICAO does not recommend any slope forshoulders

FAA specification For taxiway shoulders

Max. 5 percent for first 3 meters

2 percent thereafter

4 cm drop from paved surface to graded shouldersurface


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Longitudinal gradient

Level taxiways are operationally more desirable

If gradient is steep it affects fuel consumption

As per ICAO, maximum longitudinal gradient

3 percent for A and B type of airports

1.5 percent for C, D and E type of airport


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Grade changes are done through vertical curves

For airports A and B

ICAO recommended length of vertical curve as 25 m for

each 1 percent grade change

For airports C, D and E

ICAO recommended length of vertical curve as 30 m foreach 1 percent grade change


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TaxiwayGeometric


Available sight distance on the pavement is

affected by the rate of change of longitudinal

gradient. Maximum change in pavement longitudinal

gradient as per ICAO

4 percent for A and B category of airports

3.33 percent for C, D and E category of airports


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TaxiwayGeometric


FAA recommended distance between points of

grade change

30 |(A + B)| m

where, A and B are the percent grade changes at

the two points of grade changes along the

centerline of taxiway


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TaxiwayGeometric

Sight distance

Speed of aircraft on taxiway is lower than the

speed on runway

Smaller value of sight distance will be sufficient on thetaxiway

ICAO recommended that the surface of taxiway

must be visible at least up to a distance of X from

any point at a height of Y above the taxiwaysurface.


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Sight distance

Airport code Y X

A 1.5 m 150 mB 2 m 200 m

C,D and E 3 m 300 m


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Turning Radius

Change in aircraft path is done by providing a

horizontal curve

Design should be such that the aircraft cannegotiate the curve without significantly reducing

the speed

Recommended radii corresponding to taxing

speeds of small, subsonic and supersonic

aircrafts are 60 m, 135 m and 240 m, respectively.

Absolute min. turning radius


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Turning Radius

Relationship between exit speed and radius of

curve (turning radius)

Radius = V2/125f (m)

where, V is in kmph

f is coefficient of friction between aircraft wheel tyre

and taxiway pavement and is equal to 0.13


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Turning Radius

In case of supersonic jets

Because of long wheel base (30-35 m) the midpoint

of main gear goes off centerline of taxiway


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Turning

Radius


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Turning Radius

According to Prof. R. Horonjeff for supersonic

aircraft

The radius of curve should be such that a minimum

distance of 6 m is maintained between oleo strut of

the nearby main gear and the edge of pavement

R = 0.388W2/(0.5TS),


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TaxiwayGeometric

Turning Radius

According to Prof. R. Horonjeff for supersonic

aircraft

R = Radius of taxiway (m)

W = Wheel base of aircraft (m)

T = Width of taxiway pavement (m)

S = Distance between midpoint of the maingears and edge of taxiway pavement (m)

= 6 + (Wheel tread of main gear/2)


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Turning Radius

Determine radius of a taxiway for a supersonic

transport whose wheel base is 35 m and tread

of main gear is 7.2 m. The design turningspeed is 60 kmph.


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Fillets

This is the extra wide area provided at the curves

and traffic lane intersections so that rear wheel

does not go off the pavement edge Minimum radii of fillet is dependent on

Angle of intersection of traffic lanes

Wheel base of turning aircraft


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Fillets

The radius is not specified for wheel base greater

than 20 m

To be determined graphically using the path of nosegear


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TaxiwayGeometric

Fillets

Angle of Radii of fillet (in meters)

Intersection Small airport Large airport

0450

7.50 22.50450- 1350 15.00 30.00

> 1350 60.00 60.00

The radii of fillet should not be less than the width of

taxiway


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Fillets For Small Airports


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Fillets For Large Airports


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Separation Clearance

For safety, min. separation and clearance

standards for taxiways have been estimated

through field test As per FAA, separation clearance is based on

wing span (W)

Taxiway centre line to 1.25W + 2.1 m

taxiway center line

Taxiway centre line to obstacle 0.75W + 2.1 m


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As per ICAO, minimum separation between parallel

taxiway centerline is given by

STT= W + 2 U1+C1

W = Wing span of most demanding aircraft

U1 = Min. clearance between edge of each taxiway

and outer main gear wheels

= Taxiway edge safety margin

C1 = Min. wing tip clearance


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As per ICAO, required separation between a taxiway

centerline and a fixed or moveable object

STO= 0.5W + U1+ C2

C2 = Required clearance between wing tip and object


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As per ICAO, in meters

Minimum Separation Aerodrome Code

A B C D E

Edge safety margin 1.5 2.25 3* 4.5 4.5

Min wing tip clearance 3 3 4.5 7.5 7.5

Min. clearance bet wing 4.5 5.25 7.5 12 12

tip and object

* 4.5 m if intended to be used by the airplane with a wheel

base equal to or greater than 18 m

ce-461 ce-461 taxiway geometric design(1)

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