When you look up a runway in the Airport/Facility Directory (A/FD, now called the Chart Supplement) or an instrument approach chart, you typically see a single number labeled "runway length." For most small general aviation airports, that number tells the whole story. But at airports that have stopways, clearways, or displaced thresholds, that single number can be misleading — or even dangerous to rely on. The FAA has established four declared distances that precisely define what portion of the runway environment is available for each phase of a takeoff or landing. Understanding these values not only protects you on checkrides and knowledge tests, it protects you in the real world whenever you operate at a complex airport or fly a heavier aircraft that requires careful performance planning.
The four declared distances are: Takeoff Run Available (TORA), Takeoff Distance Available (TODA), Accelerate-Stop Distance Available (ASDA), and Landing Distance Available (LDA). Each one answers a specific question: How far can I roll during a normal takeoff? How much room is there for liftoff plus initial climb over an obstacle? If I abort, how far can I decelerate? And how much runway do I actually have for landing? Let's break each one down thoroughly.
The Physical Elements of the Runway Environment
Before defining the four distances, it helps to understand the physical features they reference. The runway itself is the paved surface prepared for aircraft takeoff and landing. Beyond the runway end, there may be a stopway — a paved or specially prepared area that can support an aircraft during an aborted takeoff deceleration, but is not intended for normal use during takeoff roll. Alongside or beyond the runway there may be a clearway — an obstacle-free zone (not necessarily paved) that extends beyond the runway end in which an aircraft may continue its initial climb after becoming airborne. Finally, a displaced threshold marks a landing threshold that is moved inward from the physical runway beginning, usually because of obstacles on approach or pavement conditions near the runway end. The area between the physical runway start and a displaced threshold is still available for takeoff roll and landing rollout — just not for the landing touchdown.
Takeoff Run Available (TORA)
TORA is the length of runway declared available and suitable for the ground run of an aircraft taking off. In simple terms, it is the pavement you can actually use from the moment you push the throttle forward until the wheels leave the ground (or until the end of your planned takeoff roll). At most airports, TORA equals the published runway length. However, if a runway incorporates a displaced threshold, that does not affect TORA when departing from the full runway end — you are taking off from the end of the physical pavement, not from the threshold. TORA does not include any stopway or clearway; those are additional features that influence the other distances.
Takeoff Distance Available (TODA)
TODA extends the concept of TORA by adding any clearway beyond the runway end. Formally, TODA equals TORA plus the length of the clearway (if one exists). The clearway represents obstacle-free airspace — typically 500 feet wide — that allows a multi-engine aircraft to achieve screen height after liftoff without worrying about obstructions. For performance calculations, TODA is therefore always equal to or greater than TORA. At airports with no clearway, TODA and TORA are identical. For turbine-powered transport category airplanes, the clearway length used in performance calculations cannot exceed half of TORA (a Part 25 performance rule), and the clearway must be under the airport's control. For a typical light single-engine airplane at a simple GA airport, you will almost never encounter a formal clearway, but the concept is heavily tested and critical for transport-category operations.
Accelerate-Stop Distance Available (ASDA)
ASDA is the distance available for an aircraft to accelerate to a decision speed and, if the takeoff is rejected, decelerate to a stop. ASDA equals TORA plus the length of any stopway beyond the runway end. Because a stopway is engineered to handle an aircraft's weight during braking (unlike a clearway, which may be unpaved), it legitimately extends how far you can safely decelerate. This makes ASDA equal to or greater than TORA. If the runway has both a stopway and no clearway, then ASDA will be greater than TODA. The reverse can also be true: a runway with a clearway but no stopway will have TODA greater than ASDA. At most small airports, ASDA equals TORA because there is no stopway. The stopway is identified by yellow chevron markings on the pavement and is not available for takeoff acceleration or landing.
Landing Distance Available (LDA)
LDA is the runway length declared available and suitable for the ground roll during landing. If the runway has a displaced threshold, LDA is measured from that threshold to the far end of the runway, not from the physical beginning of the pavement. This means LDA can be significantly less than the full pavement length. A displaced threshold is shown on runway diagrams and airport charts with a dashed centerline leading up to it, plus arrows pointing toward the threshold. The area before a displaced threshold may be used for takeoff roll and rollout after landing, but the touchdown zone for landing starts at the displaced threshold. Therefore, a runway might have a TORA of 6,000 feet but an LDA of only 5,200 feet if the threshold is displaced 800 feet for obstacle clearance on approach.
Why Declared Distances Matter
For light single-engine training aircraft at sea level on a cool day, runway performance margins are usually generous enough that declared distances seem academic. But as soon as density altitude rises, you add weight, or you operate at an unfamiliar airport, these distinctions can be life-or-death. A pilot who assumes the full 6,000-foot pavement is available for landing — when 800 feet of it precedes a displaced threshold — will have 13% less stopping distance than planned. Similarly, a pilot planning a departure with an engine-failure contingency needs to know whether ASDA covers the reject scenario. Transport-category flight operations regulations require manufacturers to publish performance data against declared distances; understanding the underlying definitions makes that data meaningful.
Declared distances are published in the Chart Supplement U.S. for domestic airports and are depicted on airport diagrams. The FAA's guidance on runway declared distances is grounded in the Pilot's Handbook of Aeronautical Knowledge and is consistent with international ICAO standards, making this knowledge transferable when flying abroad as well.
Key Numbers and Rules
- TORA = usable takeoff roll distance (runway pavement only; no stopway, no clearway).
- TODA = TORA + clearway length (for turbine-powered transport category airplanes, clearway used in performance calculations ≤ ½ TORA per Part 25; clearway must be obstacle-free and under airport control).
- ASDA = TORA + stopway length (stopway must bear aircraft weight for braking; marked with yellow chevrons).
- LDA = runway length from the landing threshold to the far runway end; reduced by any displaced threshold.
- A displaced threshold area can be used for takeoff roll and landing rollout, but not for touchdown.
- Stopway pavement is not usable for takeoff acceleration or landing touchdown/rollout.
- Clearway is not paved runway; it only provides obstacle clearance for the climb phase after liftoff.
- When no stopway or clearway exists, TORA = TODA = ASDA, and LDA equals runway length only if the threshold is not displaced.
Common Test Traps
- Confusing TODA and ASDA. Students often mix these up because both extend beyond TORA. Remember: TODA adds a clearway (airborne obstacle clearance, not for rolling), while ASDA adds a stopway (braking surface). Think of "D" in TODA as relating to distance through the air, and "S" in ASDA as Stop.
- Assuming LDA equals runway length. If a displaced threshold exists, LDA is shorter than the total pavement. The test may give you a runway length and then state the threshold is displaced — you must subtract the displacement from LDA accordingly.
- Using the stopway for takeoff acceleration. The stopway looks like runway pavement and is tempting to use, but it is not certified for takeoff roll. Its yellow chevrons are the warning sign; any calculation of takeoff ground roll uses only TORA.
- Forgetting that displaced threshold pavement can be used for rollout. After landing, you may use the pavement before the displaced threshold to decelerate — just not for touchdown. This nuance trips up students who think the entire pre-threshold area is off-limits.
- Assuming small GA airports always publish all four declared distances. The FAA only requires airports to publish declared distances when they differ from the physical runway length. If TORA, TODA, ASDA, and LDA all equal the runway length, only the runway length is published. When you see all four values listed, that's your cue that the airport has stopways, clearways, or a displaced threshold.
Mastering declared distances gives you a more complete picture of any runway you operate on. It also builds the habit of asking "how much runway do I really have?" rather than accepting the first number you see — a habit that pays dividends throughout your flying career.