Declared Distances
Declared distances are standardized runway length values published for each runway at an airport, including TORA, TODA, ASDA, and LDA. These values are essentia...
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Airport Operations
Flight Planning
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Runway Length – Distance Between Runway Ends: Airport Planning Glossary
Overview
Runway length is the measured distance between the two ends (thresholds) of a runway. This essential parameter underpins airport planning, design, and daily operations, directly influencing the types of aircraft that an airport can safely accommodate. Determining and publishing accurate runway length—along with the four associated declared distances: TORA, TODA, ASDA, and LDA—is vital for compliance with both national and international standards (such as FAA AC 150/5325-4B, AC 150/5300-13B, and ICAO Annex 14).
Declared distances provide pilots, dispatchers, and airport planners with the information necessary to calculate safe takeoff and landing performance. These measurements are central to runway analysis, aircraft certification, regulatory compliance, and risk mitigation for all classes of aviation activity, from general aviation (GA) to commercial air carriers.
Understanding these distances ensures informed decision-making regarding runway design, operational limitations, and future airport expansion. This glossary entry covers definitions, regulatory requirements, calculation methods, and operational implications of runway length and declared distances, incorporating guidance from FAA, ICAO, and industry best practices.
1. Definitions: Key Terms in Runway Length and Declared Distances
1.1 Runway Length
Runway length is the linear distance measured from one runway threshold (end) to the opposite threshold, typically expressed in feet or meters. The physical runway length refers to the total constructed pavement, including any displaced thresholds, stopways, and clearways. However, operationally usable lengths may be reduced by displaced thresholds, runway safety areas, obstacles within approach or departure paths, or other declared distance limitations.
- Physical Runway Length: The total constructed pavement.
- Usable Runway Length: The segment available for aircraft to perform takeoff or landing, which may be less than the physical length.
ICAO Annex 14 specifies that runway length should be measured along the centerline between the designated thresholds. This is critical for flight planning, as performance calculations must be based on the declared, not just physical, length.
Pilots and flight planners should always consult current airport charts (such as FAA Chart Supplement or Jeppesen diagrams) to determine the usable runway length for each operation.
1.2 Declared Distances
Declared distances are the officially published values for each runway direction and indicate maximum lengths available for specific phases of aircraft operation:
| Declared Distance | Definition | Operational Use |
|---|---|---|
| TORA (Takeoff Run Available) | Length of runway declared available and suitable for the ground run during takeoff. | Used for acceleration and lift-off calculations. |
| TODA (Takeoff Distance Available) | TORA plus any available clearway. | Used when a clearway is present, in takeoff performance calculations. |
| ASDA (Accelerate-Stop Distance Available) | Length of runway plus any stopway for acceleration and deceleration during an aborted takeoff. | Used for rejected takeoff calculations. |
| LDA (Landing Distance Available) | Length available and suitable for landing and rollout. | Used for landing performance calculations. |
Declared distances are published for each runway direction and may differ due to displaced thresholds, obstacles, or airport geometry.
1.3 Supporting Terms
- Clearway: A defined area beyond the runway, free of obstacles and suitable for the aircraft’s initial climb, but not for ground roll. Increases TODA, not TORA or ASDA.
- Stopway: A prepared surface beyond the runway, capable of supporting an aircraft during an aborted takeoff. Included in ASDA, but not in TORA or TODA.
- Runway Safety Area (RSA): A surface surrounding the runway, intended to reduce the risk of damage to aircraft in the event of an overrun, undershoot, or excursion. Not included in declared distances.
2. Declared Distances: Technical Explanation and Operational Use
2.1 TORA: Takeoff Run Available
TORA is the runway length declared available for the ground run during takeoff. It typically starts at the runway threshold and ends before the runway safety area or any obstacle. TORA is the critical value for acceleration and liftoff distance.
Pilots must use published TORA values for each runway direction, as these can differ based on airport geometry, displaced thresholds, or operational restrictions.
2.2 TODA: Takeoff Distance Available
TODA is the sum of TORA plus the length of any available clearway (an obstacle-free area beyond the runway). TODA provides extra distance for aircraft to reach a safe altitude in case of engine failure during initial climb. Not all airports have a clearway; if not, TODA equals TORA.
Example: If a runway has a TORA of 7,000 feet and a 1,000-foot clearway, the TODA is 8,000 feet.
Aircraft must be airborne before entering the clearway.
2.3 ASDA: Accelerate-Stop Distance Available
ASDA is the length of runway plus any stopway available for an aircraft to accelerate for takeoff and, if necessary, abort and come to a complete stop. ASDA is critical for rejected takeoff scenarios.
Formula: ASDA = Runway Length (usable for accelerate-stop) + Stopway Length
Stopways are marked with yellow chevrons and must be structurally capable of supporting aircraft during deceleration.
2.4 LDA: Landing Distance Available
LDA is the length of runway available and suitable for landing rollout, starting at the landing threshold. Displaced thresholds or obstacles may reduce the LDA below the physical runway length.
Pilots must always reference the published LDA for landing performance calculations.
3. Declared Distance Components: Clearway and Stopway
3.1 Clearway
A clearway is a rectangular area beyond the runway, under airport authority control, free of obstacles, and intended for the aircraft’s initial climb. It is not constructed for ground operations and is marked with yellow chevrons.
- Increases TODA, but not TORA or ASDA.
- Aircraft must be airborne before entering the clearway.
- ICAO and FAA specify minimum design and maintenance standards.
3.2 Stopway
A stopway is a prepared surface aligned with the runway, designed to support an aircraft during an aborted takeoff. It is marked with yellow chevrons and included only in ASDA.
- Must be at least as wide as the runway.
- Used only for rejected takeoff scenarios.
- Strictly regulated for strength and safety.
4. Regulatory Framework and Calculation Methodology
4.1 FAA and ICAO Standards
Runway design and declared distances are governed by:
| Regulation / Standard | Scope |
|---|---|
| FAA AC 150/5325-4B | Runway length requirements based on aircraft type, weight, elevation, temperature, and gradient. |
| FAA AC 150/5300-13B | Airport design standards, runway geometry, safety areas, published declared distances. |
| ICAO Annex 14 | International standards for aerodrome design, runway length, and declared distances. |
Compliance is mandatory for FAA-funded airports and ICAO member states.
4.2 Five-Step FAA Procedure for Runway Length Determination
- Identify Critical Design Aircraft: Aircraft expected to use the runway regularly.
- Determine Aircraft with Longest Requirement: Assess which need the greatest runway length at MTOW.
- Select Design Approach: Use group approach or individual analysis.
- Select Preliminary Runway Length: Use guidelines and performance curves.
- Apply Adjustments: Adjust for gradient, elevation, temperature, and site-specific factors.
This process ensures safe accommodation of intended aircraft.
4.3 Declared Distance Publication
Declared distances must be published for each runway direction in airport directories, master plans, and approach charts to ensure all operators have access to accurate, up-to-date data.
5. Factors Affecting Runway Length Determination
| Factor | Effect on Required Runway Length |
|---|---|
| Aircraft Type | Larger/heavier aircraft require longer runway lengths. |
| Maximum Takeoff Weight (MTOW) | Higher weights = greater required lengths. |
| Airport Elevation | Higher elevation reduces air density, increasing required length. |
| Temperature | Higher temperatures (density altitude) increase required distances. |
| Runway Gradient | Uphill increases, downhill may decrease required length. |
| Runway Surface Condition | Wet or contaminated surfaces require longer distances. |
| Obstacles | Approach/departure obstacles can require displaced thresholds, reducing declared distances. |
| Wind Conditions | Headwinds reduce, tailwinds or crosswinds increase required length. |
| Runway Configuration | Displaced thresholds, clearways, and stopways affect declared distances. |
6. Operational Implications
Proper understanding and application of runway length and declared distances are critical for:
- Aircraft Performance: Ensuring safe takeoff and landing at published weights.
- Regulatory Compliance: Meeting FAA and ICAO requirements.
- Airport Operations: Maximizing safety and capacity.
- Future Planning: Accommodating new aircraft types and increased traffic.
Airports must regularly review and update declared distances as conditions change due to construction, obstacles, or changes in operational requirements.
7. References and Further Reading
- FAA AC 150/5325-4B: Runway Length Requirements
- FAA AC 150/5300-13B: Airport Design
- ICAO Annex 14: Aerodrome Design and Operations
Summary
Runway length—and its four declared distances—form the foundation of safe, efficient airport operations and planning. Accurate measurement, regular publication, and diligent compliance with FAA and ICAO standards ensure that airports remain capable of supporting current and future aviation needs.
For airport operators, planners, and pilots, understanding and applying these concepts is essential for regulatory compliance, operational safety, and the continued growth of the aviation sector.