Declared distances are used to determine takeoff and landing performance for aircraft. It bridges the gap between aircraft performance calculations and runway design criteria.
Declared distances are required for all airports served by Part 121 operations. There are four declared distances for each runway that correlates to specific aircraft performance calculations.
- Takeoff Run Available (TORA) – The runway length declared available and suitable for the ground run of an airplane taking off.
- Takeoff Distance Available (TODA) – The takeoff run available plus the length of any remaining runway or clearway beyond the far end of the takeoff run available.
- Accelerate−Stop Distance Available (ASDA) – The runway plus stopway length declared available and suitable for the acceleration and deceleration of an airplane aborting a takeoff.
- Landing Distance Available (LDA) − The runway length declared available and suitable for a landing airplane.
Declared distances can be shorter than the length of the runway when airport runway standards are not sufficient. The runway elements of Runway Safety Area (RSA), Runway Object Free Area (ROFA), and Runway Protection Zone (RPZ) may reduce a runway’s declared distances to less than the physical length of the runway at geographically constrained airports
Reference FAA AIM 4-3-6
Aircraft performance can be categorized as balanced or unbalanced for takeoff field length calculations.
For balanced field length performance, the single runway distance number must be lower than both TORA and ASDA values.
For unbalanced field length performance, the accelerate-go distance must be less than TODA and the accelerate-stop distance must be less than TORA.