Runway Geometrics

Various elements

Runway length- basic runway length, correction

- runway orientation, configuration

Runway geometrics- length, width, imaginary surfaces, SD, separation of runways,

gradients…etc

Runway capacity

RUNWAY GEOMETRICS

Airport design standards

To provide assistance to airport designers and a reasonable amount of uniformity in the airport facilities for aircraft operations, design guidelines have been prepared by FAA and ICAO

Airport classification

-for stipulating geometric design standards for various types of airports- alphabetic and numeric codes- to classify airports

-FAA- airport reference code- based on airport aircraft approach category ad airplane design group

Airport classification…. continued

ICAO- two element code- aerodrome reference code- to classify the geometric design standards

-numeric designer( 1 to 4) – length available

-Alphabetic( A to E)- to classify the wingspan and outer gearwheel span for the aircraft for which airport is designed

Runway length requirements

Parallel-runway spacing

Depends on VMC /IMC, simultaneous arrivals and departures

Under VMC(FAA) - 300 ft for single – engine propeller aircraft; 500 ft for twin engine propeller aircraft; 700 ft for other

When operate in same direction; no wake vortices

ICAO- 400 ft for aerodrome code1; 500 ft for 2; 700 ft for 3 and 4 codes

Under IMC- 4300 ft (FAA0 and 500 ft (ICAO)

Geometrics of Runways

- runway system consists of structural pavement; shoulders; blast pad; runway safety area, various obstruction free surface and runway protection zone

Structural pavement;

Shoulders;

Blast pad;

Runway safety area(RSA)

Various obstruction free surface

Runway protection zone

Width: -

governed mainly by the wheel track and lateral wander of the aircrafts. Considering these, ICAO has developed standards for different airport categories.

Runway dimensional standards for aircraft in approach categories C,D and E

Longitudinal profile:

From the point of aircraft operation, it is desirable to minimize longitudinal grade as much as possible.

ICAO - specifications for maximum gradients and also for maximum change in grade and number of changes for different categories of airports

It is also specifies that, for runways equipped to be used in bad weather, the gradient of the first quarter(L/4) and the last quarter of the length of the runway must be very flat foe reasons of safety. ICAO recommends that this gradient not to exceed 0.8%.

Transverse gradient:

For drainage- Besides, it is recommended that a 5% transverse gradient be provided for the first 3m of shoulder adjacent to the pavement for proper drainage.

Runway Surface Gradient standards

    Sight distance:

-keeping in mind intersections between runways and taxiways/other runways.

-ICAO -for individual runways requires that the runway profile permit an unobstructed view between any two points at a specified height above the runway center line.

-The points should be mutually visible for a distance equal to at least one half the runway length. The specified heights are as follows:

Airport code Height(m)

A 1.5

B 2.0

C, D & E 3.0

Runway surface Gradient standards

Runway capacity : capability of the runway system to process aircrafts.

Number of aircrafts that the runway or runways can accommodate in a specified period of time.

Unit of time - hour or a year (hourly or annual capacity)

Capacity analysis -very complex because it depends on a large number of varying factors such as, aircraft mix, their spacing, whether approach is controlled by VFR or IFR, number and positions of exit taxiway etc

Capacity has been defined in two types:

a) saturation capacity

b) practical capacity

Saturation capacity or the ultimate capacity - maximum number of aircraft operations that the runway system can accommodate during a specified interval of time when there is a continuous demand for service, that is, there is always an aircraft ready to take off or land. But this does not take into consideration delay to the aircraft

Practical capacity, - used in the USA, is the number of aircraft operations during a specified period of time, corresponding to a tolerable level of average delay.

Depending on the period of time being an hour or a year, the capacity is termed as Practical Hourly Capacity (PHOCAP) or Practical Annual Capacity (PANCAP).

FAA -developed models for calculating PHOCAP and PANCAP for different situations.

-presented in the form of charts and tables in a capacity manual.

Saturation (or Ultimate or maximum) Capacity

This, unlike the practical capacity concept, is not related to delay, that is, capacity when there is a continuous demand for service.

Saturation (or Ultimate or maximum) Capacity

FAA has developed several models to arrive at the capacity.

In these models, the capacity is equal to the inverse of weighted average service time of all the aircrafts.

Runway service time is defined as the separation time in air between arrivals in terms of time or the runway occupancy time whichever is larger.

The separation time is taken as per the minimum air traffic separation rules or the practical observed separations if no rules apply.

Saturation (or Ultimate or maximum) Capacity

[For example, if runway service time is 90seconds, capacity is 1 operation in 90secs, that is, 3600/90 = 40 operations/hour].