To become knowledgeable about the aerodrome layout, as regards to runways and taxiway.
a) Declared Distances
Take-off run available (TORA);
The length of runway declared available and suitable for the ground run of an aeroplane taking off.
Accelerate-stop distance available (ASDA);
The length of the take-off run available plus the length of the stopway, if provided.
Take‑off distance available (TODA),
The length of the take-off run available plus the length of the clearway, if provided.
Landing distance available (LDA)
The length of runway which is declared available and suitable for the ground run of an aeroplane landing.
b) Calculate Declared Distances for Various Runways
The declared distances to be calculated for each runway direction comprise: the take-off run available (TORA), take-off distance available (TODA), accelerate-stop distance available (ASDA), and landing distance available (LDA).
Where a runway is not provided with a stopway or clearway and the threshold is located at the extremity of the runway, the four declared distances should normally be equal to the length of the runway.
Where a runway is provided with a clearway (CWY), then the TODA will include the length of clearway.
Where a runway is provided with a stopway (SWY), then the ASDA will include the length of stopway.
Where a runway has a displaced threshold, then the LDA will be reduced by the distance the threshold is displaced. A displaced threshold affects only the LDA for approaches made to that threshold, all declared distances for operations in the reciprocal direction are unaffected.
A runway provided with a clearway or a stopway or having a displaced threshold.
Where more than one of these features exists, then more than one of the declared distances will be modified - but the modification will follow the same principle illustrated.
If a runway direction cannot be used for take-off or landing, or both, because it is operationally forbidden, then this should be declared and the words "not usable" or the abbreviation “NU” entered in the AIP data
c) How Declared Distances are Used by Aircraft Operators
Declared distances are used by aircraft operators to determine whether an aircraft can use a runway for take-off or landing. This determination is based on many factors.
the type of aircraft (light/medium/heavy)
the weather conditions (wind-direction/speed/cross-wind component)
the runway conditions (dry/wet/ice/snow)
the all up weight (AUW) of the aircraft given the above runway conditions;
thereby determining the take-off speed and therefore the distance to accelerate to that speed, and the distance to stop in the event of a rejected take-off. Also the distance required to land the aircraft and to decelerate to a stop.
The flight crew have this information readily available in the cockpit to determine whether or not they can accept the runway, we as controllers offer them, for 0take-off or landing.