032 Performance topic guide
TORA, TODA, ASDA and LDA Explained
TORA, TODA, ASDA and LDA are the four declared distances published for every runway direction, and almost every take-off and landing performance question is really asking you to pick the right one of the four before any arithmetic starts. TORA is the take-off run available, the physical runway length usable for the ground roll. TODA adds any clearway to TORA, and ASDA adds any stopway to TORA.
LDA, the landing distance available, is a separate figure again: the runway length from the threshold in use, or from a displaced threshold where one exists, to the far end. Clearway and stopway never touch LDA; they exist purely on the take-off side, which is why a runway can offer generous take-off distances while its landing distance stays limited by the threshold position alone.
What each distance means
Each of the four figures answers a different operational question, and mixing them up changes which case is actually being limited.
- TORA: the take-off run available, the runway length itself.
- TODA: TORA plus clearway, credited to the accelerate-go, continued take-off case.
- ASDA: TORA plus stopway, credited to the accelerate-stop, rejected take-off case.
- LDA: the landing distance available, measured from the threshold in use to the runway end.
Clearway and stopway are not the same thing
Clearway is an area beyond the runway end, under the airport authority's control, that the aeroplane only ever overflies after becoming airborne on its climb to the 35 ft screen height. It never has to bear the aeroplane's weight, and it is credited only to the continued take-off case, through TODA.
Stopway is different in kind: a prepared surface capable of supporting the aeroplane during a rejected take-off, so it can be rolled onto and braked on, and it is credited only to the rejected take-off case, through ASDA. Crediting clearway to a stopping calculation, or stopway to a climb calculation, produces a distance that looks plausible but was never available for that case.
Which distance limits which certification case
The all-engines take-off run itself is limited by TORA. The continued take-off after a failure, from lift-off to the screen height, is limited by TODA. A rejected take-off, from V1 to a full stop, is limited by ASDA. Landing, from the threshold to a full stop with the required margin, is limited by LDA.
A displaced threshold is worth remembering here: the displaced portion can still count toward TORA, TODA and ASDA for take-off purposes if it is structurally suitable, but it is removed from LDA, because landing must not begin before the threshold.
Worked example
Worked example: building TODA and ASDA
Not quite. The correct answer is C.
Correct answer: C
- A. This swaps the two extensions: clearway feeds TODA, not ASDA, and stopway feeds ASDA, not TODA.
- B. This adds both the clearway and the stopway into TODA (2500 + 300 + 200), double-counting the stopway on the continued take-off side, where it has no role.
- C. Correct. TODA = TORA + clearway = 2500 + 300 = 2800 m. ASDA = TORA + stopway = 2500 + 200 = 2700 m.
- D. This gets TODA right but forgets to add the stopway to ASDA, leaving it as TORA alone.
Step by step
- Match each extension to its distance: clearway belongs to TODA, stopway belongs to ASDA, and neither belongs to the other.
- TODA = TORA + clearway = 2500 + 300 = 2800 m.
- ASDA = TORA + stopway = 2500 + 200 = 2700 m.
- Sanity check: both figures exceed TORA by exactly one extension each, never by both together.
Common mistakes
Swapping clearway and stopway
Clearway extends TODA and stopway extends ASDA. Swap them and every distance-limited calculation that follows uses the wrong available distance for the case being tested.
Adding both extensions into the same distance
Clearway and stopway are credited to different cases. Adding both to TODA, or both to ASDA, overstates the distance actually available for that specific case.
Assuming LDA always equals TORA
A displaced threshold, a different landing direction, or published landing-only restrictions can make LDA smaller than TORA even on the same physical runway.
Related topic guides
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Last reviewed July 2026