ASDA – Accelerate-Stop Distance Available: Aviation Glossary

Declared Distances in Airport Planning and Flight Operations

Declared distances are vital regulatory values set by airport authorities (per ICAO Annex 14 and FAA AC 150/5300-13B) to specify the maximum portions of a runway and associated areas available for takeoff, rejected takeoff, and landing. The four principal declared distances are:

• Takeoff Run Available (TORA)
• Takeoff Distance Available (TODA)
• Accelerate-Stop Distance Available (ASDA)
• Landing Distance Available (LDA)

These values are critical for safety, compliance, and precise aircraft performance calculations. They are not always equal to the physical runway length due to factors like stopways, clearways, displaced thresholds, and safety or obstacle protection requirements. Understanding and correctly applying each declared distance is essential for safe and compliant airport and flight operations.

Accelerate-Stop Distance Available (ASDA): Definition and Purpose

ASDA is the length of runway plus any declared stopway available for an aircraft to accelerate from a standstill to the takeoff decision speed (V1), and, if necessary, abort the takeoff and come to a complete stop. The airport authority determines and publishes this value.

• Source: ICAO Annex 14, FAA AIM 4-3-9
• Use: It defines the maximum distance available for rejected takeoff procedures.
• Requirement: The aircraft’s accelerate-stop distance required, as calculated per the Aircraft Flight Manual (AFM) or Pilot’s Operating Handbook (POH), must not exceed the published ASDA.
• Inclusion: If a stopway is declared, it is included in ASDA; otherwise, ASDA is limited to usable runway length.

ASDA is always based on thorough safety and regulatory assessments, including runway safety areas (RSA), runway protection zones (RPZ), and obstacle evaluation. Operators and pilots must always use the published ASDA, not the physical runway length, for all takeoff performance calculations.

Declared Runway Distances: Comprehensive Definitions

Takeoff Run Available (TORA)

TORA is the length of runway declared suitable for the aircraft’s ground run during takeoff. It usually matches the physical runway, but may be shorter due to safety area requirements.

Key points:

• Does not include stopway or clearway.
• Essential for takeoff roll calculations.
• Always check official airport documentation for TORA.

Takeoff Distance Available (TODA)

TODA is the sum of TORA and any declared clearway. The clearway is an obstacle-free area beyond the runway, not required to support aircraft weight or be load-bearing.

Key points:

• Only aircraft certified to use clearways may include TODA in calculations.
• The aircraft must become airborne before the end of the runway (TORA).

Accelerate-Stop Distance Available (ASDA)

ASDA is the declared length of runway plus any stopway available for an aircraft to accelerate to the takeoff decision speed and, if necessary, abort the takeoff and stop safely.

Key points:

• Stopways are included only in ASDA.
• If the aircraft’s accelerate-stop distance required exceeds ASDA, takeoff is not permitted.

Landing Distance Available (LDA)

LDA is the length of runway declared suitable for landing, measured from the (possibly displaced) threshold to the runway end. It does not include stopways or clearways.

Key points:

• Landings must be completed within the LDA.
• Displaced thresholds and obstacles may reduce LDA.

Runway Features Affecting Declared Distances

Stopways

A stopway is a prepared area at least as wide as the runway, suitable to support an aircraft during an aborted takeoff, but not for normal use. Only included in ASDA; not in TORA, TODA, or LDA.

Clearways

A clearway is an obstacle-free area beyond the runway end, controlled by the airport, and not required to be load-bearing. Used only in TODA for certified operations.

Displaced Thresholds

A displaced threshold is a landing threshold located away from the physical runway start, often due to obstacles or pavement issues. Landings must occur beyond the displaced threshold.

Runway Safety Areas (RSA) and Runway Protection Zones (RPZ)

RSA is a graded, cleared area to minimize aircraft damage during overruns or excursions. RPZ is a ground area beyond the runway end for public safety. Both can result in reductions to declared distances if minimum standards are not met.

ASDA Compared to Physical Runway Length

ASDA may be shorter, equal to, or longer than the physical runway due to:

• Inclusion of stopways (ASDA > runway length)
• Regulatory or physical constraints (ASDA < runway length)
• Obstacles, insufficient safety areas, or land-use restrictions

Important: Always use only the declared ASDA, never assume it equals the physical runway length.

Balanced and Unbalanced Field Lengths: Impact on ASDA

Balanced Field Length

Runway length at which accelerate-go and accelerate-stop distances are equal. ASDA is the limiting factor for balanced field calculations.

Unbalanced Field Length

Used when ASDA or other declared distances create asymmetric constraints; calculations may favor either accelerate-stop or accelerate-go, as supported by aircraft data and regulations.

Practical Application of ASDA in Operations

Flight Planning

• Obtain declared distances (TORA, TODA, ASDA, LDA) from official sources.
• Calculate aircraft performance using AFM/POH.
• Ensure required accelerate-stop distance does not exceed ASDA.
• Adjust weight, configuration, or runway selection as needed.

Airport Planning

• Declared distances are determined by physical features, safety requirements, and operational needs.
• Stopways may be built to increase ASDA.
• Declared distances may be “paper” reduced due to obstacles or safety area limitations.

Real-World Examples of ASDA and Declared Distances

ASDA Shorter Than TORA

• Teterboro (KTEB) Runway 01: Physical length 7,000 ft, ASDA 6,090 ft due to RPZ land use.
• Naples (KAPF) Runway 14: Physical length 5,000 ft, ASDA 4,550 ft due to nearby road.
• Similar constraints exist at major airports like Anchorage, Miami, Atlanta, Chicago O’Hare, and Dallas Love Field.

ASDA Longer Than TORA

• If a 1,000-ft stopway is built on a 6,000-ft runway, ASDA becomes 7,000 ft (if compliant with all safety and regulatory requirements).

Use Cases and Scenarios Involving ASDA

• Takeoff Performance Limitation: If required accelerate-stop distance exceeds ASDA, reduce weight or select a different runway.
• Engine Failure at V1: ASDA ensures sufficient distance to stop safely after a rejected takeoff.
• Regulatory Compliance: Using anything other than declared ASDA for performance is a violation and safety risk.

Common Pitfalls and Operational Advisories

• Do not use physical runway, stopway, or clearway for performance calculations unless officially declared as part of ASDA.
• Always verify current published declared distances for each runway end.
• Displaced thresholds reduce LDA and may impact other declared distances.
• Monitor for changes in declared distances due to construction or regulations.
• Using non-declared values is prohibited and unsafe.

Locating Declared Distances

Declared distances are published in:

• FAA Chart Supplement (A/FD)
• Jeppesen Airport Charts
• ICAO Aeronautical Information Publications (AIPs)
• Canada Flight Supplement
• Look for the “inverted D” symbol on US charts.

Related Terms and Concepts

Runway Safety Area (RSA)

A graded area to minimize aircraft damage during overruns or excursions. If RSA cannot be provided, declared distances may be reduced.

Runway Protection Zone (RPZ)

Ground area for safety of people and property beyond the runway; strict land-use controls apply.

Engineered Materials Arresting System (EMAS)

A bed of crushable material at the runway end for overrunning aircraft. EMAS may allow shorter declared distances or mitigate for insufficient RSAs, but is not part of declared distances unless published.

Displaced Threshold

A landing threshold set away from the runway start, reducing LDA and possibly affecting other declared distances.

Summary

ASDA is a safety-critical, declared runway distance representing the maximum length available for an aircraft to accelerate to V1 and, if necessary, stop safely during a rejected takeoff. It is determined and published by airport authorities and may differ from the physical runway length due to the inclusion of stopways or regulatory constraints. Correct understanding and application of ASDA, along with other declared distances (TORA, TODA, LDA), are essential for safe, compliant, and efficient flight and airport operations. Always consult current, official sources for declared distances, and never use physical dimensions or assumptions for performance calculations.