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Transportation Engineering - II
Runway Length
Dr. Indrajit Ghosh
Assistant Professor
Department of Civil Engineering
Indian Institute of Technology Roorkee
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Lecture Outline
Basic Runway Length
Corrections to basic runway length
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Basic Runway length
Length calculated under the following assumed
conditions:
Airport is situated at sea-level
Standard temperature of 15o
C at the airport Runway is leveled in longitudinal direction
Zero effective gradient
No wind is blowing on runway
Aircraft is loaded to its full loading capacity No wind is blowing on the way to destination
Standard temperature exists along the way
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Basic Runway Length: Factors Affecting
Determination of basic runway length
Performance characteristics of aircrafts using the
airport
Manner in which an aircraft actually performs landingand take off operation
Consideration of following cases
Normal Landing
Normal Take-off
Engine Failure
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Basic Runway Length: Factors Affecting
Normal Landing
The aircraft should come to a stop within 60 percent
of landing distance assuming that the pilot makes an
approach at the proper approach speed and crossesthe threshold of the runway at a height of 15 m (50
ft)
The runway of full strength pavement is to be
provided for the entire landing distance
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Basic Runway Length: Factors Affecting
Normal Landing
Runway (Full strength)
15mStop
60% of landing distance
TouchdownPoint
RunwayThreshold
Landing Distance
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Basic Runway Length: Factors Affecting
Normal Landing: Calculations
Field length (FL) = Landing distance (LD)
LD = Stopping distance (SD) / 0.60
Length of full strength runway (FS) = LD
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Basic Runway Length: Factors Affecting
Normal Take-off
Take-off distance must be, for a specific weight of
aircraft, 115 percent of the actual distance the aircraft
uses to reach a height of 10.5 m (35 ft) It requires a clearway at the end of the runway in the
direction of take-off
This should not be less than 150 m wide
It is kept free from obstructions
The upward slope of clearway from the end of the
runway shall not exceed 1.25 percent
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Basic Runway Length: Factors Affecting
Normal Take-off
Runway (Full strength)
10.5m
Lift off distance
115% of LOD
Distance to reach a height of 10.5mTake-off Distance
(115% of distance to 10.5 mheight)
Clearway >Half thisdistance
Clearway
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Basic Runway Length: Factors Affecting
Normal Take-off
Runway (Full Strength) Clearway
Min. 150 m
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Basic Runway Length: Factors Affecting
Normal Take-off
Clearway
A rectangular area at the end of landing strip in the direction of
take off
Centrally located about extended centre line of runway
Selected or prepared as suitable area over which an aircraft
may take a portion of its initial climb to a specified height
Under the control of airport authorities
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Basic Runway Length: Factors Affecting
Normal Take-off: Calculations
Field length (FL) = Full strength runway (FS) + Clearway
(CW)
Take-off distance (TOD) = 1.15 D10.5m Clearway (CW) = 0.5[TOD - 1.15(LOD)]
Take-off Run (TOR) = TOD - CW
Length of full strength runway (FS) = Take-off run (TOR)
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Basic Runway Length: Factors Affecting
Engine Failure
If the engine fails at a speed, less than designated
engine failure speed, pilot decelerates the aircraft and
makes use of a stopway If, however, engine fails at a speed higher than the
designated speed, there is no other option to the pilot
except to continue to take-off
Pilot may later take a turn in turning zone and land again for anormal take-off
Requires either a clearway, or a stopway, or both
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Basic Runway Length: Factors Affecting
Engine Failure
Stopway
A rectangular paved area at the end of runway in the direction
of take-off in which an aircraft can be stopped after aninterrupted take-off due to engine failure
Its width is at least equal to the width of runway
It is centrally located in alignment with centre line of runway
Used for decelerating aircraft and bringing it to a stop during
an aborted take-off
Strength of stopway pavement should be just sufficient to
carry the weight of the aircraft without causing any structural
damage to aircraft
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Basic Runway Length: Factors Affecting
Engine Failure
Decelerate - Stop Distance
Runway (Full strength)
10.5
m
Lift off distance
Stop way
Accelerate - Stop Distance
Take-off Distance
(distance to 10.5 m height)
Engine Failure
Accelerate to V1
Lift-off
Point
Clearway > Half this
distance
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Basic Runway Length: Factors Affecting
Engine Failure
Runway (Full Strength)
Clearway
minimum
150 m
Stopway
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Basic Runway Length: Factors Affecting
Engine Failure: Related calculations
Take-off proceeded case
Take-off distance (TOD) = D10.5m
Clearway (CW) = 0.5 [TOD - LOD]
Take-off Run (TOR) = TOD - CW
Length of full strength runway (FS) = Take-off run
(TOR)
Field length (FL) = Full strength runway (FS) +
Clearway (CW)
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Basic Runway Length: Factors Affecting
Engine Failure: Related calculations
Take-off aborted case
Field length (FL) = Full strength runway (FS) +
Stopway (SW)
FL = Accelerate stop distance (ASD)
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Basic Runway length
Required runway length
In case of Jet engine aircrafts
All the three conditions are considered
The case giving the longest runway length isfinally recommended
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Basic Runway length
Required field length and other components
Field length = max {LD, TOD2, TOD3, ASD}
Full strength runway = max {LD, TOR2, TOR3}
Stopway = ASD - max {LD, TOR2, TOR3} Clearway = min {(FL - DAS), CW2, CW3}
Stopwaymin= 0
Clearwaymin= 0
Clearwaymax= 300 m
If both ends of runway are to be used by aircrafts
Field length components must exist in each direction
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Basic Runway length
ICAO Specifications for Field Runway
Length
Specify four Declared Distances as
Takeoff run available (TORA)
Takeoff Distance available (TODA) {=TORA +
Clearway}
Accelerate Stop distance available (ASDA)
{=TORA + stopway}
Landing distance Available (LDA)
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Basic Runway length
ICAO Specifications for Field Runway Length
Specify five cases as
I:with no CL and SW and with no displaced threshold
the four declared distances are normally equal to thelength of runway
II:When runway is provided with a CL, TODA will
include the CL
III:When runway is provided with SW, ASDA willinclude the length of SW
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Basic Runway length
ICAO Specifications for Field Runway Length
Specify five cases as
IV:When runway has a displaced threshold, LDA will
be reduced by the distance the threshold is displaced.The displaced threshold at one end affects LDA for
approaches made to the threshold.
V:When a CL, SW and a displaced threshold is
provided
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Basic Runway length
ICAO declared distances
C L
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Basic Runway length
ICAO declared distances
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Basic Runway length
ICAO declared distances
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Basic Runway length
Example problem
Determine the runway length requirement for
turbine powered aircraft. Following aircraft
performance characteristics are observed. Normal landing
Stop distance = 1500 m
Normal take off
Lift off distance = 2100 m
Distance of 10.5 m height = 2400 m
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Basic Runway length
Example problem (continued)
Engine failure take off
Lift off distance = 2460 m
Distance of 10.5 m height = 2730 m Accelerate stop distance = 2850 m
Engine failure aborted take off
Accelerate stop distance = 2850 m
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Basic Runway length
Corrections for Elevation, Temperature and
Gradient
Basic runway length is for mean sea level
(MSL) elevation Have standard atmospheric condition
Have zero effective gradient
Necessary corrections are applied Any change in elevation, temperature and gradient
for the actual site of construction
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Basic Runway length
Correction for elevation
Elevation increases
Air density reduces
Reduces the lift on wings of aircrafts Require greater ground speed to rise to air
Need longer length of runway
ICAO recommendation
Basic runway length should be increased
At rate of 7 percent per 300 m rise in elevation of
airport above mean sea level
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Basic Runway length
Correction for elevation
Airport elevation = 100 m
Basic length of runway = 600 m
Calculate actual length of runway.
Correction for elevation
= (7/100)* (100/300) * 600
= 14 m
Length of runway after correction for elevation
= 600 + 14 = 614 m
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Basic Runway length
Correction for temperature
Rise in airport reference temperature hassame effect as that of increase in elevation
above MSL ICAO recommendation
Initially basic runway length is corrected forelevation of airport
Basic runway length is further increased at rate of 1percent for every 10 C rise in airport referencetemperature above standard atmospherictemperature at that elevation
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Basic Runway length
Correction for temperature
Airport Reference Temperature AFT = T1+
1/3 (T2- T1)
T1= Monthly mean of average dailytemperature for the hottest month of the year
T2= Monthly mean of the maximum dailytemperature for the same month
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Basic Runway length
Correction for temperature
Airport Reference Temperature
Daily temp. data for hottest month of a year
for a given airport siteDate Temp Date Temp
Max Avg. Max Avg.
1 48.0 27.7 16 47.7 26.8
2 47.3 27.5 17 48.5 27.2
. .
15 46.5 27.1 30 46.1 27.3
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Basic Runway length
Temperature
Standard Temperature at airport site at anelevation (in o C)
STE = [Temp at MSLrate of change of temp.x elevation]
= (15 - r x h )
Standard temperature at MSL is 15oC
r is rate of change of temperature with heightabove MSL 6.50 C / 1000 m rise in elevation
h is height above MSL in meters
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Basic Runway length
Correction for elevation and temp.
Airport elevation = 100 m
Basic length of runway = 600 m
Airport reference temp. = 28o C
We found earlier,
Length of runway after correction for elevation
= 600 + 14 = 614 m
Standard temp. at airport site
= 15(6.5*100/1000) = 14.35 o C
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Basic Runway length
Correction for elevation and temp.
Rise in temp. = 28 -14.35= 13.65 o C
Correction for temp.
= (1/100 * 614) *13.65 = 83.81 = 84 m
Corrected runway length after elevation plus
temp. correction
= 614 + 84 = 698 m
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Basic Runway length
Check for total correction for elevation plus
temp.
ICAO recommendation
Total correction should not exceed 35 percent of
basic runway length
If exceeds, the corrections should then be further
checked up by conducting specific studies at the
airport site by model sites
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Basic Runway length
Correction for elevation and temp.
Corrected runway length after both corrections
= 698 m
Total correction in percentage
=(698600)/600 * 100
= 16.33% < 35%
Hence, OK
Not done now
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Basic Runway length
Correction for gradient
Runway Gradient
Runway gradients are of two types:
Longitudinal gradient
Transverse gradient
Quick disposal of water from the pavement surface
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Basic Runway length
Correction for gradient
Runway Gradient
Longitudinal gradient
If the gradient is steep it may cause pre-mature lift-off
or may induce structural defects
It will cause more consumption of energy and will
require longer length of runway to attain the desired
ground speed
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Basic Runway length
Correction for gradient
Runway Gradient
ICAO does not recommend any specific correction
FAA recommendation
Runway length to be increased at a rate of 10 percent
for every 1 percent of the effective gradient
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Basic Runway length
Correction for gradient
Runway Gradient
Effective longitudinal gradient
Average gradient, computed based on difference in
maximum and minimum elevation along the runway
and divided by the total length of runway
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Basic Runway length
Correction for elevation, temp. and gradient
Airport elevation = 100 m
Basic length of runway = 600 m
Airport reference temp. = 28o C
Highest point along length = 98.2 m
Lowest point along length = 95.2 m
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Basic Runway length
Correction for elevation, temp. and gradient
Effective gradient = (98.2 - 95.2 )/600
= 3/600 = 0.5%
Correction for gradient
= 10/100 * 698 * 0.5
= 34.9 = 35 m
Actual length of runway
= 698 + 35 = 733 m
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Basic Runway length
Corrections to basic runway length Elevation correction
Temperature correction
Gradient correction
These corrections have to be applied in the samesequence as listed above
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Basic Runway length
Corrections to basic runway length
Elevation Correction rate
le= 7 percent per 300m rise above MSL
Temperature Correction rate
lt= 1 percent for every 1orise in ART above Std.
Atmospheric temp at that elevation
Gradient Correction rate
lg= 10 percent for every 1 percent of effective gradient
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Basic Runway length
Example problem
Longitudinal section of runway provides
following data:
Calculate effective gradient of runway.
End to end of runway (m) Gradient (%)
0 to 200 +1
200 to 600 -1
600 to 1200 +0.8
1200 to 1600 +0.2
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Example
Mean of avg daily temp = 40 degree C
Mean of max daily temp = 50 degree C
Site is at MSL
Basic runway length = 800 m
Determine actual runway length.
Runway is on a level surface