An airport consists of several components out of which runways form the most important part of any airport design. The design of an airport runway involves finding the length of the runway. The length of an airport runway depends on a number of factors. Also, different corrections need to be applied before arriving at the final runway length for a proposed site. In this blog, we have covered the basic runway length calculation. Corrections required will be covered in our next blog.
Factors Affecting Runway Length
There are two important factors that affect the runway length.
Aircraft characteristics - some aircraft can take off and land within shorter runway lengths while other aircraft may require longer runways. Therefore, runway length must be designed for critical aircraft, i.e., one requiring a longer length of the runway for landing or take-off.
The maximum of the three below-mentioned cases also affects the runway length.
Normal landing
Normal take-off
Emergency landing
Normal Landing Case
According to this case, critical aircraft's stopping distance must be exactly equal to 60% of runway length (or landing distance), for safety reasons. Therefore, runway length by considering this condition will be,
Runway length = Stopping distance / 0.6
Normal Take-off Case
According to this case, take off length i.e., the sum of runway length and clearway length must be greater than 115% of runway length. Note that, the clear length is a portion of take-off length that is greater in width and is provided for safety purposes in case of failures.
Take-off length (= runway length + clearway length) > 115 % of runway length
Emergency Landing / Engine Failure Case
If in case an aircraft's engine fails, an extra distance is required for stopping the aircraft. This extra distance is provided within the clearway length for completely stopping the aircraft.
Assumptions in Calculating Basic Runway Length
There are certain assumptions in finding this basic runway length that may or may not be true in all cases. This is where corrections come into the picture if all or some of the assumptions are not met. Listed below are the assumptions considered.
Airport altitude is at sea level
The temperature of the airport is at standard 15°C
No gradient
No wind flow on the runway
The airport is loaded to full capacity
Runway Width
The width of a runway depends on two factors as given below.
Wheel load from the aircraft
The machinery of an aircraft should not go outside the runway width
ICAO recommends runway width based on the type of airport. It recommends a 45m width of runway for the type-A airport.
Refer to the below-given video lecture on basic runway length for more insights and an example problem.
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