When it comes to flight planning, a lot more goes into takeoffs and landings than meets the eye. Pilots and dispatchers rely on a series of precisely calculated runway distances—known as declared distances—to make sure aircraft can take off, land, or even abort a takeoff safely. These aren’t just numbers—they’re the foundation of flight safety.
✈️ What Are Declared Distances?
Declared distances define the maximum runway lengths available and suitable for aircraft performance, covering everything from normal takeoffs to rejected ones and landings. The four key types are:
v TORA (Take-Off Run Available)
v TODA (Take-Off Distance Available)
v ASDA (Accelerate-Stop Distance Available)
v LDA (Landing Distance Available)
Some airports may also have a Displaed Threshold, which is a threshold located at a certain point along the runway, not necessarily at the physical beginning, used to protect Obstacle Clearance.
Let’s break each one down.
1. TORA – Take-Off Run Available
TORA is the actual length of paved runway available for the aircraft’s ground roll—from brake release until liftoff. In other words, it is the length of runway declared available for the take-off run, from the threshold to the stopway or the end of the runway.
v It’s the go-to number for pilots to determine whether there’s enough room to hit takeoff speed.
v If TORA is short, it might restrict aircraft performance, limit payload, or require modified procedures.
v Wet runway? Forget about using the clearway—the aircraft must lift off and reach 15 feet by the end of the runway itself.
2. TODA – Take-Off Distance Available
TODA includes TORA plus the clearway—an obstacle-free area beyond the runway.
v This full stretch is factored in for the airborne portion of takeoff.
v Useful when a pilot needs that extra space to get airborne and clear any obstacles safely.
v Think of TODA as the runway plus a bit of a boost.
3. ASDA – Accelerate-Stop Distance Available
This one’s crucial for emergencies. ASDA is the length of runway (and possibly stopway) available to accelerate up to V1 (decision speed) and then safely abort the takeoff if needed.
v It must account for aircraft weight, conditions, and available stopping power like reverse thrust or brakes.
v At V1, the pilot must commit—either go or stop. ASDA gives the space to do the latter safely.
⚠️ Can ASDA Be Shorter Than TORA?
Yes, especially at airports in the U.S. Why? Sometimes, the area beyond the runway isn’t suitable as a stopway due to land use restrictions (like roads or buildings). That makes the ASDA shorter, even if the runway looks long enough.
Example: At Teterboro (KTEB), Runway 01 has a TORA of 7,000 feet—but the ASDA is only 6,090 feet due to land constraints. Charts may not always show this, which can mislead pilots if not accounted for in planning.
4. LDA – Landing Distance Available
LDA is the length from the runway threshold to the end of the runway that can be used for landing and stopping.
v Landing performance is measured from a 50 ft threshold crossing to a full stop.
v Pilots must ensure that the landing distance required (LDR) doesn’t exceed the LDA—especially in wet or slippery conditions.
Clearways vs. Stopways: Know the Difference
At many runways, you’ll find clearways and stopways extending beyond the runway. Though they might look similar, their purposes are quite different.
✅ Clearway
v A clearway is a paved or unpaved, obstacle-free area beyond the runway, at the end of the declared take-off run, which can be used for acceleration during take-off. It must have a specified slope.
v It's used only for continued takeoff, giving extra room after liftoff.
v It doesn’t need to support the weight of an aircraft.
✅ Stopway
v A stopway is a prepared surface aligned with the runway, used to support aircraft that abort a takeoff past V1. It is not suitable for take-off but helps in emergencies.
v Must be as wide as the runway, strong enough to bear aircraft weight, and clearly marked with chevrons or lights.
v Acts like a safety net in high-speed abort scenarios.
Some airports even feature EMAS (Engineered Materials Arresting Systems)—specially engineered surfaces designed to quickly decelerate aircraft that overrun the runway.
Balanced vs. Unbalanced Field Length
✈️ Balanced Field Length
Here, the accelerate-go and accelerate-stop distances are equal. The limiting factor becomes whichever is shortest among TORA, TODA, or ASDA.
v Great for simplicity in performance planning.
v If one distance is reduced—say, ASDA is shorter—the available field length for takeoff is automatically reduced too.
In this case, performance is split:
v Accelerate-stop is compared only to ASDA
v Accelerate-go is based on TORA + clearway
This lets the operator optimize performance based on specific conditions or aircraft configuration.
✍️ Final Thoughts
Whether you're preparing a takeoff roll at a major international hub or landing on a shorter regional strip, declared distances are the data backbone of your performance planning.
Understanding the roles of TORA, TODA, ASDA, and LDA, and the function of clearways and stopways, helps pilots make safe, informed decisions—especially during high-stakes moments like an abort or emergency.
Always check your airport charts, NOTAMs, and aircraft performance data carefully. Because in aviation, runway length isn’t just about how long it is—it’s about how usable.
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