How to Calculate Declared Distances (TORA, TODA, ASDA, LDA)
Declared distances are the four published runway lengths an operator may use for takeoff and landing performance: TORA, TODA, ASDA, and LDA. They are governed by AC 150/5300-13B, Appendix H. On a clean runway with no clearway, stopway, or displaced threshold, all four equal the physical runway length — the work begins the moment one of those features appears. This is a planner’s walk-through of each definition and a worked example for both ends of a runway.
The four declared distances
Each declared distance answers a specific performance question for one operational direction of a runway. The FAA defines them in Appendix H as follows.
TORA — Takeoff Run Available
The TORA is the length of runway declared available and suitable for satisfying takeoff-run requirements — the ground run of an airplane taking off. The start of takeoff for TORA, TODA, and ASDA is always co-located, and it is most often the beginning of the runway. TORA can never be longer than TODA.
TODA — Takeoff Distance Available
The TODA is the TORA plus the length of any remaining runway or clearway beyond the departure end of the TORA. A clearway is a defined area beyond the runway end, under airport control, over which the initial climb to a specified height may be made. A clearway only affects the TODA. The TODA may also be deliberately shortened to mitigate a penetration of the 40:1 instrument departure surface — in which case the TORA is limited to the length of the TODA.
ASDA — Accelerate-Stop Distance Available
The ASDA is the length of runway plus stopway (if any) declared available and suitable for satisfying accelerate-stop requirements for a rejected takeoff. A stopway is a defined area beyond the runway end able to support an airplane during an aborted takeoff. A stopway only affects the ASDA, and a stopway can never be part of the LDA.
LDA — Landing Distance Available
The LDA is the length of runway declared available and suitable for satisfying landing-distance requirements. The LDA begins at the threshold. When threshold-siting, RSA, ROFA, and approach-RPZ standards are met, the threshold sits at the beginning of the runway; when they are not, displacing the threshold is an option — and that displacement reduces the LDA for landings toward that threshold.
The default case
When a runway has no clearway, no stopway, and no displaced threshold — and the start of takeoff is at the runway beginning — all four declared distances equal the full physical runway length:
TORA = TODA = ASDA = LDA = full runway length
That is the baseline every runway end starts from. Each feature then adjusts exactly one distance, in one direction:
- Clearway → adds to TODA only.
- Stopway → adds to ASDA only.
- Displaced threshold → reduces LDA only (for landings toward that threshold), by the displacement distance.
The displaced-threshold pavement is not wasted in the other directions: that paving can still count toward TORA, TODA, and ASDA for takeoffs in either direction, and toward the LDA when landing from the opposite end.
A worked example
Take a hypothetical 6,000 ft runway designated 09/27. Suppose the 09 end carries a 400 ft displaced threshold, and the 27 end has a 300 ft stopway plus a 500 ft clearway. With the start of takeoff at each physical runway end, the arithmetic works out direction by direction.
For Runway 09 (taking off and landing toward the displaced 09 threshold side): the displaced threshold only reduces landing length. So TORA = TODA = ASDA = 6,000 ft, and LDA = 6,000 − 400 = 5,600 ft.
For Runway 27 (the stopway-and-clearway end): the clearway adds to TODA, the stopway adds to ASDA, and there is no displacement on this end. So TORA = 6,000 ft, TODA = 6,000 + 500 = 6,500 ft, ASDA = 6,000 + 300 = 6,300 ft, and LDA = 6,000 ft.
| Runway end | TORA | TODA | ASDA | LDA | Driver |
|---|---|---|---|---|---|
| 09 | 6,000 | 6,000 | 6,000 | 5,600 | 400 ft displaced threshold → LDA |
| 27 | 6,000 | 6,500 | 6,300 | 6,000 | 500 ft clearway → TODA; 300 ft stopway → ASDA |
All values are in feet. This is an illustrative example, not a real facility — the point is the pattern: each feature moves exactly one column, and every other column stays at the runway length.
Downstream consequence: RPZ anchoring
Declared distances are not just performance numbers — they relocate runway surfaces. AvPlot follows the convention that the departure RPZ anchors to the TORA end, not the ASDA end. Because TORA, TODA, and ASDA can each end at a different station once a clearway or stopway is present, picking the right reference end matters: the departure RPZ keys off where the takeoff run is declared to end, while the approach RPZ keys off the threshold (and therefore moves with a displacement).
Where to find authoritative values
For US runways, declared distances are published per runway end in the FAA NASR subscription — the 28-day data set AvPlot reads from. That means you can pull the current authoritative TORA, TODA, ASDA, and LDA for an existing facility rather than back-calculating them, and every value carries a cycle date for the citation trail. When you are planning a change — adding a stopway, displacing a threshold, shortening a TODA for a departure-surface penetration — the Appendix H rules above tell you which distance moves and by how much.
This article is a reference summary for planning use, not a substitute for the governing FAA text. Citations refer to AC 150/5300-13B (Airport Design), Appendix H, Change 1, dated August 16, 2024. The worked example is hypothetical. Always verify declared distances against current NASR data and the governing AC before issuing a design product. See the full airport planning glossary or the AvPlot toolkit.