Airport Geometric Standard

Topics to be coveredRunway lengthRunway widthSight distanceGrades and change of gradesTaxiwaysApronsOrientation of runwayWind Rose diagram.

Aircraft characteristics

1. Type of propulsion: the size of aircraft, its

circling radius, speed, weight carrying

capacity, noise and heat nuisance etc.

depends on type of propulsion.

Piston engine.

Jet engine.

2. Size of aircraft :

Wing span

Fuselage length

Height (empennage height)

Distance between main gear

Wheel base and

Tail width.

3. Minimum turning radius : is very essential in

order to decide the radius of taxiway,

position of aircrafts in landing aprons and

hangers and to establish the path of the

movement of the aircraft.

4. Circling radius : depends on type of aircraft,

air traffic volume and weather condition.

Micro-lites aircraft – 1.6km

Jet engine – 80km

5. Speed of aircraft : Cruising speed/ground speed – aircraft speed

w.r.t ground when aircraft is flying in air @ maximum speed.

Air speed – speed of aircraft relative to wind.6. Aircraft capacity : capacity of runway system

and passenger terminal.7. Weight of aircraft and wheel configuration :

structural design of runway, taxiway, apron and hangers.

8. Jet blast : causes inconvenience to the

passenger travelling in aircraft. Bituminous

flexible pavements are affected by the jet blast,

CC pavements @ touch down portion. For

location, position and size of gates.

9. Fuel spillage : bituminous flexible pavements are

seriously effected by the fuel spillage.

10. Noise.

Runway orientation• Runway is always oriented in the direction of

prevailing winds.• The direction of wind opp. to the direction of

landing and take-off (head wind) provide greater lift on the wings of aircraft when it is taking-off and during landing head wind provides a breaking effect and the aircraft comes to stop in a shorter length of a runway.

• Landing and taking-off along wind direction require longer runway.

Cross wind : If a wind blow making certain angle with a

center line of runway then it has two components, one along the direction of runway center line VcosƟ and normal to the direction of runway center line VsinƟ. Where V is the velocity of wind.

The normal component of the wind is called the cross wind component and may interrupt the safe landing and take-off of the aircraft.

Depends on size & wing configuration. Small aircraft <15kmph & mixed traffic <25kmph(FAA), big aircrafts <35kmph(ICAO)

Wind coverage : The percentage of time in a year during which

the cross wind component remains within the limits (as per FAA & ICAO specification) is called wind coverage.

A/C to FAA, the runway handling mixed traffic should be so planned that 95% of time in a year, the permissible cross wind component does not exceed 25kmph.

For busy airport, the wind coverage may be increased to as much as 98% to 100%.

Wind Rose• The graphical representation of direction, duration

and intensity of wind obtained from wind data is called wind rose.

• Wind data – at least 5yrs, preferably 10yrs.• Wind rose diagram helps in analyzing the wind data

and obtaining the most suitable direction of the runway.

• The percentage of time during which the intensity of wind is < 6.4(6)kmph is called calm period.

• Wind rose diagram is plotted in two types• Type I: showing direction and duration of wind• Type II: showing direction, duration and intensity of

wind

Wind rose diagram - Type I• The radial line indicate the wind direction and

each circle represents the duration of wind.• The values of percentage of time in a year during

which wind blows from different direction are plotted along the corresponding directions. All plotted points are then joined by straight line.

• The best direction of runway is usually along the direction of longest line on wind rose diagram.

• Does not account the effect of cross wind component.

Wind rose diagram – Type II• Circle represents the wind intensity to some scale. The values in each

segments represents the percentage of time in a year during the wind blows with particular intensity form the respective direction.

• The procedure for determining the orientation of runway is as follows:• Step1 : draw three equally spaced parallel lines on a transparent paper

strip in such a way that the distance between the two near by parallel lines is equal to the permissible cross wind component. This distance is measured with same scale with which wind rose diagram is drawn.

• Step2 : place the transparent paper strip over the wind rose diagram in such a way that the central line passes through the centre of the diagram.

• Step3 : with the centre of the wind rose, rotate the tracing paper and place it in such a position that the sum of all values indicating the duration of wind, with in two outer parallel lines, is the maximum. The runway should thus oriented along the direction indicated by central line. The wind coverage can be calculated by summing up all the percentages shown in segment. The percentage value is assumed to be equally distributed over the entire area of the segment.

Change in direction of runway• Obstructions

• Excessive grading

• Noise nuisance

Length of runway

• Selecting the length of a runway is per haps

the important decision which must be made in

the planning of landing area.

• Length of runway depends on

1.The type of aircraft

2.Its payload

Basic runway lengthIt is the length of runway under the following

assumed condition at the airport:1.Airport altitude at sea level2.Temperature at airport is standard (150 c)3.Runway is leveled in the longitudinal direction4.No wind is blowing on runway5.Aircraft is loaded at its full loading capacity6.There is no wind blowing en route to the

destination7.En route temperature is standard

• The following case are considered for

determining the basic runway length

1.Normal landing case

2.Normal take-off case

3.Engine failure case

The cases which works out the longest

runway length is finally adopted

Jet engine

Piston engine

1. Normal landing case• The normal landing case requires that an air

craft should come to a stop within 60% of the landing distance. The runway of full strength pavement is provided for the entire landing distance.

15 m

stop

60% of landing distance

landing distance

Runway

2. Normal take-off case

• The normal take-off case requires a clearway which

is an area beyond the runway and is in alignment

with the centre line of runway. The width of

clearway is not <150m and is kept free from

obstruction. The clearway ground area or any

object on it should not protrude a plane inclined

upward at a slope of 1.25% from the runway.

Lift-off distance

115% of Lift-off distance

Distance to 10.5m height

115% of distance to 10.5m height ( take-off distance)

Clearway ≤ ½ of this distance

10.5m height

Longitudinal section

Runway Clearway

Min 150m

Plan

Normal Take-off Case

3.Engine Failure Case• The engine failure case may require either a clearway, or

a stop way, or both.• Stop way is an area beyond the runway and centrally

located in alignment with the centre line of runway. • Stop way is used for decelerating the aircraft and

bringing it to stop during aborted take-off.• If the engine has failed at a speed, less than the

designated engine failure speed, the pilot decelerate the aircraft and make use of stop way.

• If however, the engine fails at a speed higher than the designated speed, there is no other option to the pilot except to continue take-off. The pilot may later take a turn in the turning zone and land again for a normal take-off.

Lift-off distance

Accelerated stop distance

Distance to 10.5m height ( take-of distance )

Clearway ≤ ½ of this distance

10.5m height

Longitudinal section

Runway

Clearway Min 150m

Plan

Engine Failure Case

Engine Failure

Decelerated – stop distance

Stop wayClear way

Stop way

Correction for Elevation, Temperature and Gradient

• The basic runway length is for mean sea level

elevation having standard atmospheric

conditions.

• For any change in elevation, temperature and

gradient for actual site of construction,

necessary corrections are to be applied to

obtain the length of runway.

Correction for Elevation• The air density reduces as the elevation

increases, this in turn reduces the lift on the

wings of the aircraft and the aircraft requires

greater ground speed before aircraft becomes

airborne. To achieve greater speed, longer length

of runway is required.

• ICAO recommends that basic runway length

should be increased at the rate of 7% per 300m

rise in elevation above MSL.

Correction for Temperature• The rise in airport reference temperature has the same

effect as that of the increase in elevation.• Airport reference temperature

Ta = monthly mean of avg. daily temp. for the hottest month of the year.

Tm = monthly mean of the maximum daily temp. ICAO – 1% for every 10c rise in airport reference temp. Further the temp. gradient of the standard atmosphere

from the mean sea level to the altitude at which the temp becomes 15.60 c is 0.00650 c per meter.

= Ta + (Tm – Ta )/3

Check for total correction for elevation plus temperature

• ICAO further recommends if the total

correction for elevation plus temp. exceeds

35% of the basic length, these correction

should be further checked up by conducting

specific studies at the site by model test.

Correction for gradient• Steeper gradient results in greater

consumption of energy.• ICAO does not recommends any specific

correction for the gradient.• FAA – Runway length after being corrected for

elevation and temp. should be further increased at the rate of 20% for every 1% of specific gradient.

• Specific gradient – is the max. difference in elevation between the highest and lowest point of runway divided by the total length of runway.

Runway width• ICAO recommends the pavement width varying

from 18m to 45m for different types of aircraft.• The width of runway pavement depends upon the transverse

distribution of traffic at a distance from the center line of runway pavement. It is found that the aircraft traffic is more concentrated in the central 24m width of the runway pavements.

• Another consideration in determining the runway width is that the outer most machine of larger jet aircraft using the airport should not extend off the pavement on to the shoulders. This is because the shoulder is usually of loose soil or established soil etc. which is likely to get into the engine and damage it.

Width and length of safety area• Safety area consists of the runway plus the

shoulder on either side of runway plus the area that is cleared, graded and drained.

• The shoulder are usually unpaved as they are used during emergency. The shoulders on the either side of runway impart a sense of openness to the pilot and improve his psychology during landing and take off.

• The length of the safety area is equal to the length of runway plus 120m.

Type Width of safety area (As per ICAO standards)

A,B and C D and E

Non-Instrumental runway

150m 78m

Instrumental runway 300m (min)

Transverse gradient• Transverse gradient is essential for quick

drainage of surface water.

Description Gradient (As per ICAO standards)

Type

A,B and C D and E

Runway 1.50% (max) 2.0% (max)

Shoulders Within a distance of 75m from the center line of runway transverse gradient should not exceed 2.5% and for remaining portion of shoulder, the transverse gradient should not exceed 5%

Longitudinal and Effective Gradient

Description Type

A,B and C D and E

Longitudinal Gradient 1.5% 2%

Effective Gradient 1% 2%

Rate of change of longitudinal gradient

Description Type

A and B C D and E

Rate of change of longitudinal

gradient (As per ICAS Standards)

0.1% (max) per 30m length of vertical

curve

0.2% (max) per 30m length of vertical

curve

0.4% (max) per 30m length of vertical

curve

Distance between two successive points of grade

intersections (D)

>300(a+b)…..m >150(a+b)…..m >49.5(a+b)…..m

FAA recommendations for longitudinal grade changes in runway

Description Type

Small airport Large airport

Max. grade change such as ‘a’ or ‘b’ should

not exceed

2% 1.5%

Length of vertical curve (L1 or L2) for each one percent grade change

90m 300m

Distance between two successive points of

grade intersections (D)

75(a+b)…..m 300(a+b)…..m

Taxiway• Taxiway provides access to the aircrafts from

the runways to the loading apron or service hanger and back.

Runway and Taxiway

Runway

Taxiway

Taxiway

Factors to be considered for layout of taxiway Taxiway should be so arranged that the

aircrafts which have just landed and taxiing towards the apron, do not interfere with the aircrafts taxiing for take-off.

At the busy airport, taxiway should be located at various points along the runway so that the landing aircraft leaves the runway as early as possible and keeps it clear for use by other aircrafts. Such taxiway are called exit taxiway.

The route for taxiway should be so selected that it provides the shortest practicable distance from the apron.

As for as possible, the intersection of taxiway and runway should be avoided.

Exit taxiway should be designed for high turn off speeds. This will reduce the runway occupancy time of aircraft and thus increase the airport capacity.

Geometric Design Standards For Taxiway

• Length – should be as short as practicable.• Width – lower than the runway width. This is

because the aircraft run on the taxiway are not air borne and the speed of the aircraft on taxiway is lower. Hence pilot can easily manoeuvre the aircraft over a smaller width of taxiway.

• Width of safety area – it includes width of taxiway pavement plus shoulder on either side. The width of the shoulder is 7.5m on each side and are paved with light strength material.

Type Taxiway width (m)

Max. longitudinal gradient %

Min. transverseGradient %

Max. rate of change of

longitudinal gradient per

30m, %

A 22.5 1.5 1.5 1

B 22.5 1.5 1.5 1

C 15 3 1.5 1

D 9.9 3 2 1.2

E 7.5 3 2 1.2

Taxiway Geometrics (ICAO)

FAA recommends the transverse gradient of shoulder should be 5% for first 3m and 2% for thereafter

Turning radius• Whenever there is change in direction of a taxiway,

a horizontal curve is provided. The curve is so designed that the aircraft can negotiate it without significantly reducing the speed. Circular curve with larger radius is suitable for this purpose.

• The radius is given by R = V2/127f. where; R is radius in m, V is speed in kmph and

f is 0.13.• Subsonic jet transport – min. 120m.• Supersonic jet transport – min. 180m.

• According to Horonjeff the radius of the taxiway should be so provided that the distance of the oleo strut of the nearby main gear is not less than 6m from the pavement edge.

• Horonjeff formula: R = (0.388W2) / (T/2 – S)Where; → R is the radius of the taxiway in meter→ W is the wheel base of aircraft in meter→ T is the Width of taxiway pavement in meter→ S is the distance between midway point of the main

gears and the edge of the taxiway pavement in meter.

• If the existing airport has to be upgraded to accommodate supersonic transport, it may be feasible to widen the pavement rather than increasing the radius.

• Widening is done by providing a compound curve of radii R1 and R2. the values of R1 and R2 is obtained using;

R2 = R – ((0.388W2 / R) + S)→If exp. ((0.388W2 / R) + S) < T/2, no widening is

needed. If it is > T/2, the radius R1 is R1 =(Dr2+(T/2)+0.3R- R2

2-RT/2(R- R2)

where Dr = 3W-0.4R if Dr<W then use W instead of Dr.

Widening at curves

Apron• It is a paved area for parking of aircrafts, loading

and unloading of passenger and cargo. It is usually located close to the terminal building or hangars.

• The size of the apron depends upon:→Size of loading area required called as gate

position ,for each type of aircraft.→Number of gates→Aircraft parking system:-Nose-in, Angle Nose-in,

Nose-out, Angle Nose-out, Parallel parking. (Refer text book for explanation)

Hangar• Hangar provides enclosure for servicing,

overhauling and doing repairs of the aircrafts.• Hangars are constricted of steel frame and

covered with GI sheets. They are provided with machine shops and stores for spare parts.

• The size of the hangar depends upon the size of aircraft and its turning radius.

• Hangars are provided with adequate light systems.

Hangar site location The site should such that there is a convenient road

access to it from the site to the aprons and terminal buildings.

Near to loading apron. The site should not be along the direction of

frequent storms as this is likely to damage the hangar doors etc.

Sufficient area to provide car parking facilities for working personnel and other facilities such as electricity, telephone, water supply and sewers etc.

Favorable topography providing good natural drainage and adequate site area for future expansion.