Airport Runway Length & Design Notes: Airport runways are perhaps the most visible example of a navigation aid updated to match Earth’s magnetic field shifts. Runway design is one of the most important transportation engineering subjects for GATE Civil engineering students.
Runway length topic has a good probability of getting questions of 1 or 2 marks in GATE Civil Engineering, BARC Civil, ESE Civil exams for civil engineering students. In this article, we share complete information about airport runway design, important points related to Wind-Rose diagrams, basic runway length requirements, turning radius at the taxiway, important elements of an airport & some important definitions.
Runway Design Introduction:
Runway is usually oriented in the direction of prevailing winds.
The headwind i.e. the direction of wind opposite to the direction of landing and take-off provides greater lift on the wings of the aircraft when it is taking off.
Crosswind component = V sinθ where θ = Angle of wind direction to the runway centerline
Normal component of the wind is called the wind component.
The maximum permissible crosswind component depends upon the size of the aircraft and the wing configuration.
Basic Runway Length
It is the length of runway under the following assumed conditions at the aircraft
- airport altitude is at sea level
- Temperature at the airport is standard (15°C)
- runway is leveled in the longitudinal direction.
- No wind is blowing on runway.
- Aircraft is loaded to its full loading capacity.
- There is no wind blowing enroute to the destination.
- Enroute temperature is standard.
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Corrections for Elevation, Temperature and Gradient
(a) Correction of Elevation: Basic runway length is increased at the rate of 7% per 300 m rise in elevation above the mean sea level.
(b) Correction for Temperature
Airport reference temperature
Where, Ta = monthly mean of average daily temperature
Tm = monthly mean of the max daily temperature for the same month of the year.
Total correction for elevation plus temp. ⇒ 35% of basic runway length.
(c) Correction for Gradient
- Steeper gradient results in greater consumption of energy and as such longer length of runway is required to attain the desired ground speed.
- After having been corrected for elevation and temperature should be further increased at the rate of 20% for every 1% of effective gradient.
- Effective gradient is defined as the maximum difference in elevation between the highest and lowest points of runway divided by the total length of runway.
Runway Geometric Design
- Runway Width: ICAD recommends the percent with varying from 45 m to 18 m for different type of airport.
- Safety Area: Consists of the runway, which is paved area plus the shoulder on either side of runway plus the area that is cleared, graded and drained.
For non – instrumental runway, the width of safety area should be at least 150 m for A, B, C and 78 m for D and E type and for instrumental runway, it should be minimum 300 m
- The length of safety area is equal to the length of runway plus 120 m
- Transverse gradient: Essential for quick drainage of surface water.
For A, B, C type of Airports ⇑ 1.5%
For D and E type of Airports ⇑ 2%
Transverse gradient ⇔ 0.5%
- Longitudinal gradient
A, B, C type of Airports = 1.5%
D and E type of Airports = 2.0%
For effective gradient: Max limit
A, B and C type of airports = 1.0%
D and E type of airports = 2.0%
- Rate of Change of Gradient: Should be limited to a maximum of 0.1% per 30 m length of vertical curve for A and B type, 0.2% for C type and 0.4% D and E type of airport.
Vertical curves are generally not necessary if the change in slope is not more than 0.4%
- Sight Distance: For A, B, C type of airport, any two points 3 m above the surface of runway should be mutually visible from a distance equal to half the runway length.
For D and E type of runway within a distance of at least one half the length of runway.
(i) Before planning:-
(a) To determine relation between bed rock and top soil when exploration at the surface in form of knowing morphology, petrology, stratigraphy etc.
(b) Electrical resistivity methods are used to locate positions of work zone like faults and shear zones.
(ii) At the time of planning :-
(a) Investigations at the time of planning are made through drilling holes either by
(iii) At the time of construction :-
Information is achieved by driving either of the following.
(i) Types of explosives :-
(a) Straight dynamites
(b) Ammonia dynamites
(c) Ammonia gelatine
(ii) Theory of blasting :- Processes by which rock can be blasted
(c) Thermally induced spalling
(d) Fusion and vaporization
(e) Chemical reaction
1.3. Shape and Size
(i) D-section :– This section is suitable for sub-ways or navigation tunnels.
(ii) Circular section :- For tunnels which may have to withstand heavy internal or external radial pressure.
(iii) Rectangular section: Suitable in case of hard rocks.
(iv) Egg shaped section:- Used for carrying sewage because it gives self cleaning velocity.
(v) Horse shoe form :- Used for traffic purposes and as the floor of the tunnel is nearly flat, it gives working space to store material during construction.
1.4. Various types of Construction Technique
(i) Cut and cover method (iv) Shaft method
(ii) Bored tunnel method (v) Box jacking method
(iii) Clay kicking method (iv) Under water tunnels.
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2.1. Types of Bridges
(i) Arch Bridges :-
(a) It is very strong and wide range of materials can be used.
(b) It is quiet expensive.
(ii) Truss Bridges:-
(a) It is frequently used as a draw bridge or as an overpass for railroad train.
(b) It is difficult to construct, high maintenance.
(iii) Suspension Bridges:-
(a) It has span distances up to 7000 feet,
(b) It allows large boats and heavy boat traffic to pass underneath.
(c) Expensive construction
(iv) Cable Stayed Bridges:-
(a) Not expensive and faster to build
2.2. Factors for Selection of Types of Bridges
(i) Geography (ii) Loading
(iii) Aesthetics (iv) Cost
2.3. Section Criteria for Bridge Site
(i) Topography (ii) Catchment area
(iii) Hydrology (iv) Geo-technical
(v) Seismology (vi) Navigation
(vii) Construction resources (viii) Traffic data
2.4. Types of Bridge Foundation
(i) Spread or open foundation is suitable for bridges of moderate height to be built on dry ground which is sufficiently firm to support the bridge structure.
(ii) Raft foundation is suitable when bed of water course consists of soft clay and silt.
(iii) Grillage Foundation is suitable for heavy load and located footing of piers where deep foundations are to be avoided.
(iv) Inverted arch foundation is suitable when depth of excavation for foundation is less. It is best suited where bearing capacity of soil is less.
(v) Pile formation is suitable when the soil is very soft and the hard strata are not available at reasonable depth.
(vi) Well foundation is suitable where good soil is available at about 3 to 4m below the bed level of the river the bed consist of sandy soil.
(vii) Caisson foundation is suitable when a hard is available near to the river bed but the depth of water is excessive and it is not economically possible to exclude water from a dry bed for sinking the wells to provide well foundation.
Airports are classified by 2 organisations:
(i) ICAO: International Civil Aviation Organization.
(ii) FAA: Federal Aviation Agency.
ICAO classified airport into 2 categories-
(i) Based on basic runway length
A → longest runway
B → shortest runway
- Equivalent Single Wheel Load of the aircraft.
(i) Length of runway requirements will be more if landing and take-off operation are performed along the wind direction.
(ii) Wind parameters (direction and intensity) are graphically represented by diagrams called as wind rose diagrams.
(iii) Wind parameters should be collected for a period of 3 years.
(iv) Normal component of the wind is called as cross-wind component & it may interrupt safe landing & take-off of the aircraft. For the smaller size of aircraft, max. Permissible limit is 15 km/hr & for bigger →25 km/hr of (due to more weight, its higher) of cross-wind component.
The % age of time during which in a year, the crosswind component remains within the permissible limit is called as wind coverage.
3.2. Basic runway length requirements
- Airport altitude is at MSL.
- Temperature at airport is standard 15°c.
- Runway is levelled in the longitudinal direction.
- Aircraft is loaded through its full loading capacity. They themselves are worst cases. So no correction required for them.
- Speed of wind should be zero on the runway.
Correction for Elevation
ICAO recommends that the basic runway length should be increased by 7% per 300 m rise in elevation above MSL.
Correction for Temperature
Standard atmospheric temperature at rest altitude is calculated as:
Local body temperature of a particular area is called as airport reference temperature & that is defined for hottest month of the year.
Τa → monthly mean of avg. Daily temperature.
Τm → monthly mean of max. Daily temperature.
ICAO recommends that the basic runway length after corrected for elevation should be increased by 1% for every 1°c rise of art above the std. Atmospheric temperature at that elevation (air density).
If the total correction for elevation & temperature is less than or equal to 35% of basic runway length, no corrections are >35%, scientific analysis must be performed at site conditions again (economical).
Correction for gradient
[Only as per FAA].
After corrected runway length for elevation & temperature, runway length should be increased by 20% for every 1% of effective gradient.
In case of landing, only elevation correction is necessary.
3.3. Turning radius at taxiway
4) R> 120 m for Sub sonic jets.
3.4. Some Important elements of an Airport
Stop way is used in case of engine failure conditions.
Length of runway is decided on the basis of:
- Normal landing case
- Normal take off care
- Engine failure case
Circling radius depends on
- Type of aircraft
- Weathering conditions & volume of aircrafts.
Aircraft movements will be more in case visual flight rules as compared to instrumental flight rules (which are applicable in bad weathering conditions.)
Size of hanger building is decided on basis of size of aircraft (length, width, height).
Dock, Port & Harbour
Some Important Definitions:
- HARBOURS provide safe anchorage to ships in conditions of bad weather.
- PORTS are used for loading & unloading of passengers, cargo, etc.
- Every port is a harbour but reverse is not true.
- Docks which are used for ships to facilitate loading & unloading of passengers & cargo are known as Wet Docks.
- Docks which are used for serving & maintenance of ships are called as Dry Docks.
- WHARF → it is a type of fixed platform usually on file foundations where ships are loaded or unloaded.
- FENDER → Dock wall receives large amount of impact and to avoid this, cushions are provided permanently with dock walls & these are known as FENDERS. [In India, we use TYRES].
- DOLPHIN PILES → used to tie-up the ships.
- LITTORAL DRIFT → Sea waves are generated by prevailing winds & they move lighter particles of sand in suspension. This suspended sand is carried in a zig-zag manner & deposition of this sand is called LITTORAL DRIFT.
- Excavation below water surface is called as DREDGING.