The physical length of a runway does not necessarily indicate how much distance is available for takeoff, rejected takeoff, or landing. A displaced threshold, stopway, clearway, obstacle limitation, construction project, or airport design requirement can produce different declared distances for each operation.
This is why aeronautical publications use four essential terms: TORA, TODA, ASDA and LDA.
These values represent the maximum distances officially declared available by the airport operator. They are not additional safety margins and should never be casually added to aircraft performance figures.
What are declared distances?
Declared distances are the runway lengths officially identified as available and suitable for meeting an aircraft’s takeoff-run, takeoff-distance, accelerate-stop, and landing-distance performance requirements.
A runway may have a specific physical length, yet not all of that pavement will necessarily be available for every operation. In some cases, an aircraft may begin its takeoff roll before a displaced threshold while being prohibited from touching down on that same section when landing in that direction.
Similarly, an area beyond the runway end may be included in an accelerate-stop calculation without being available for a normal takeoff ground roll.
This functional separation is the reason the four distances must be evaluated independently.
TORA — Takeoff Run Available
TORA, or Takeoff Run Available, is the runway length declared available and suitable for the ground run of an aircraft taking off.
It answers a straightforward question:
How much runway is available for the aircraft to accelerate on the ground?
At an uncomplicated airport, TORA will often equal the usable physical runway length. However, it may be shorter when part of the runway cannot be considered for takeoff-performance purposes.
A displaced threshold does not automatically reduce TORA. When the pavement before the displaced threshold is authorized and properly marked, it may remain available for takeoff even though it cannot be used for touchdown when landing in that direction.
TODA — Takeoff Distance Available
TODA, or Takeoff Distance Available, is the distance declared available for completing the takeoff.
In a conventional configuration:
TODA = TORA + clearway
A clearway is a defined area beyond the end of TORA that is kept free of obstacles so that an aircraft may complete part of its initial climb over it.
A clearway is not necessarily paved, nor is it intended for the aircraft’s ground run. It provides protected space beyond the runway rather than additional pavement on which the aircraft can accelerate.
TODA answers:
What total distance is available for the ground run and the applicable initial airborne portion of the takeoff?
The use of a clearway in performance calculations depends on the aircraft’s certification basis, operating rules and approved performance data. A pilot cannot assume that every aircraft may take full credit for a published clearway.
ASDA — Accelerate-Stop Distance Available
ASDA, or Accelerate-Stop Distance Available, is the distance declared available for the aircraft to accelerate and, if the takeoff is rejected, decelerate to a stop.
In a typical layout:
ASDA = TORA + stopway
A stopway is a prepared area beyond the end of TORA that can support the aircraft during a rejected takeoff. Its purpose is to provide additional stopping distance under the conditions for which it was designed.
A stopway is not a routine extension of the takeoff runway. It should not automatically be treated as pavement available for a normal takeoff roll, taxi operation, or landing.
ASDA answers:
How much distance is available to accelerate and then stop following a rejected takeoff?
This value is particularly important in transport-category and multiengine aircraft performance planning, where accelerate-stop and takeoff-continuation scenarios must be evaluated.
LDA — Landing Distance Available
LDA, or Landing Distance Available, is the runway length declared available and suitable for the ground run of a landing aircraft.
It begins at the landing threshold and extends to the declared end of the landing distance.
When a threshold is displaced, LDA will normally be shorter than the full pavement length because the section before the threshold is not available for touchdown when landing in that direction.
A threshold may be displaced because of obstacles in the approach path, airport design limitations, protection requirements, or other infrastructure considerations.
LDA answers:
How much runway is officially available for landing from the threshold to the declared landing-distance limit?
LDA is the distance provided by the airport. The aircraft’s landing distance required must still be calculated using the approved performance information, actual operating conditions and all applicable safety factors.
Clearway and stopway are not interchangeable
Confusing these areas can lead to a serious misunderstanding of runway performance.
| Area | Abbreviation | Primary purpose | Included in |
|---|---|---|---|
| Clearway | CWY | Obstacle-free area used for the applicable initial airborne portion of takeoff | TODA |
| Stopway | SWY | Prepared area used to decelerate and stop after a rejected takeoff | ASDA |
In practical terms:
- TODA = TORA + clearway
- ASDA = TORA + stopway
The clearway is associated with continuing the takeoff. The stopway is associated with rejecting the takeoff.
Neither area should automatically be interpreted as conventional runway pavement.
How a displaced threshold affects the distances
A displaced threshold is one of the clearest examples of why declared distances must be considered independently.
Depending on its markings, published limitations and operational status, the pavement before a displaced threshold may be available for:
- taxi;
- the beginning of a takeoff roll;
- landing rollout from the opposite direction.
However, that same section is not available for touchdown when landing toward the displaced threshold. As a result, LDA may be shorter than TORA.
The actual status must always be confirmed using the current airport diagram, Aeronautical Information Publication, Chart Supplement and applicable NOTAMs.
A practical example
Consider a runway with the following characteristics:
- TORA: 6,000 feet;
- clearway: 1,000 feet;
- stopway: 600 feet;
- displaced threshold: 500 feet.
In this simplified example:
- TORA = 6,000 ft
- TODA = 7,000 ft
- ASDA = 6,600 ft
- LDA = 5,500 ft, assuming the threshold displacement only reduces the distance available for landing in that direction.
This does not mean that the airport has a 7,000-foot paved runway. The additional 1,000 feet included in TODA represent the clearway and may only be used for the approved performance purpose.
Likewise, the 600-foot stopway does not increase the normal takeoff run available. It is included only in the accelerate-stop distance.
Available distance versus required distance
This is the most important operational distinction:
- Available distance is what the airport provides: TORA, TODA, ASDA and LDA.
- Required distance is what the aircraft needs under the actual operating conditions.
The required distance, including all applicable regulatory and operational factors, must remain within the corresponding declared distance.
The performance calculation may need to consider:
- aircraft weight;
- pressure altitude and temperature;
- wind direction and velocity;
- runway slope;
- dry, wet or contaminated runway conditions;
- flap setting;
- obstacle environment;
- engine performance;
- aircraft manual limitations;
- regulatory factors and company procedures.
A runway that appears long enough may still be inadequate under demanding environmental or aircraft-performance conditions. Conversely, using the physical pavement length without checking the declared distances can create a false impression of available performance.
Where can pilots find declared distances?
In the United States, declared distances may be published in the FAA Chart Supplement and depicted or referenced in airport information. Internationally, they are commonly found in the State’s Aeronautical Information Publication and airport charts.
Temporary changes caused by construction, maintenance, obstacles or runway closures may be published by NOTAM.
Values must be checked for the specific runway direction because the two ends of the same physical runway can have different declared distances. The FAA emphasizes that these figures represent the maximum distances available and suitable for the applicable aircraft-performance requirements. FAA Aeronautical Information Manual
Conclusion
TORA, TODA, ASDA and LDA are not simply four abbreviations printed on an airport chart. They represent four different operational requirements: accelerating on the runway, completing a takeoff, stopping after a rejected takeoff, and landing.
Understanding these differences prevents pilots from treating a clearway or stopway as ordinary runway pavement. It also avoids the assumption that the entire physical surface is equally available for every maneuver.
The correct performance-planning question is not merely:
“How long is the runway?”
It is:
“What distance has been declared available for the operation I intend to perform?”
Marcuss Silva Reis
Commercial Pilot — Fixed-Wing Aircraft | Former Civil Aviation Flight Instructor | Former University Professor of Aeronautical Sciences | Aviation Expert Witness | Economist | Postgraduate in Aeronautical Sciences, Civil Aviation Safety and Higher Education | Optical Technician
Founder of Instituto do Ar
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