LDA – Landing Distance Available: The Ultimate Glossary for Airport Planning and Flight Operations

Introduction

Landing Distance Available (LDA) is among the most vital declared runway distances in aviation, directly impacting the safety, compliance, and efficiency of flight operations and airport design. This article serves as a comprehensive glossary and reference, covering LDA’s definition, regulatory framework, technical application, and its relationship to other declared distances. It is essential reading for airport planners, flight crew, dispatchers, and anyone involved in operational decision-making for aircraft landings.

What is Landing Distance Available (LDA)?

Landing Distance Available (LDA) is the length of runway declared by an airport operator as available and suitable for the ground run of an aircraft landing. As defined by ICAO Annex 14, LDA is measured from the landing threshold (which can be displaced from the physical start of the runway) to the end of the runway surface suitable for aircraft deceleration and stop.

LDA is a published, regulatory value and not always equal to the full physical runway length. Obstacles, displaced thresholds, runway geometry, and safety zones can reduce the declared LDA. For pilots and planners, the LDA represents the actual, usable distance for landing rollout—affecting landing performance, allowable payload, and flight safety.

Declared Runway Distances: The Complete Set

Airports declare several key runway distances per ICAO and FAA standards, each serving a specific operational and regulatory function:

• Takeoff Run Available (TORA): The runway length suitable for aircraft takeoff ground run.
• Takeoff Distance Available (TODA): TORA plus any clearway (obstacle-free area beyond the runway end, used for airborne climb).
• Accelerate-Stop Distance Available (ASDA): Runway plus any stopway (specially prepared area for rejected takeoff deceleration).
• Landing Distance Available (LDA): Runway length available for landing rollout, from the landing threshold to the end of the usable runway.

These distances are published for each runway direction (e.g., Runway 09 and Runway 27), as local obstacles, displaced thresholds, and infrastructure may make them unequal.

LDA vs. Physical Runway Length

LDA ≠ Physical Runway Length

• Displaced Thresholds: LDA starts at the displaced threshold, not the runway’s physical beginning. The area prior may be used for takeoff but is unavailable for landing rollout.
• Stopways and Clearways: These extend ASDA or TODA but are not part of LDA.
• Obstacles and Safety Zones: Encroachments or reduced Runway Safety Areas (RSA) or Runway Object Free Areas (ROFA) may shorten the declared LDA.

Example:
A 3,000-meter runway with a 300-meter displaced threshold has an LDA of 2,700 meters.

Technical Deep Dive: LDA Calculation and Application

Determining LDA

• Start Point: The landing threshold (can be displaced).
• End Point: The end of the usable, suitable runway surface.
• Excludes: Any area before the threshold, stopways, clearways, and areas not meeting pavement or safety standards.

Factors Affecting LDA

• Obstacles in approach path
• Pavement strength and condition
• Runway slope and geometry
• Runway safety zones and object clearance
• Temporary restrictions (construction, maintenance)

LDA in Flight Planning

• Landing Performance: Aircraft must be able to land and come to a full stop within the LDA, using factored (safety-margined) landing distances.
• Regulatory Compliance: Operators must always use the published LDA, not the physical runway length.

Declared Distances in Context: TORA, TODA, ASDA, and LDA

Each distance has distinct impact on operational planning and aircraft performance calculations.

Supporting Terms Related to LDA

• Clearway: Obstacle-free area beyond runway for airborne climb, not for ground roll or landing.
• Stopway: Prepared area beyond runway for rejected takeoff, not for landing or takeoff roll.
• Displaced Threshold: Threshold not at the physical runway start; area before it not available for landing.
• RSA/ROFA: Safety areas clear of obstacles; their encroachment may reduce LDA.

LDA in Practice: Publication and Operational Use

• Official Sources: LDA is published in the Aeronautical Information Publication (AIP), airport directories, and charts.
• Updates: Changes from construction, obstacles, or safety zones are published via NOTAMs.
• Runway Modifications: Any change in LDA requires immediate update in official publications.

Operational Best Practice:
Always use the most current, official LDA for planning and in-flight decisions. Cross-check between AIP, NOTAMs, and airport charts if discrepancies exist.

Regulatory Requirements: ICAO, FAA, EASA

• ICAO: Annex 14 mandates LDA publication and recalculation for any significant runway or obstacle change.
• FAA: Advisory Circulars (e.g., AC 150/5300-13B) and FAR Parts 91/121/135 govern LDA use and require compliance for all operations.
• EASA: Operators must use published LDA, and in-flight calculations are required for landing under actual conditions.

Non-compliance can lead to regulatory violations and increased accident risk.

Best Practices for LDA Use

• Always verify LDA from official sources (AIP or NOTAM).
• Apply factored landing distance per regulations (usually 1.67× actual landing distance).
• Use the most restrictive published LDA if multiple sources exist.
• Update all operational documents and training with LDA changes.
• Understand interaction of LDA with displaced thresholds, stopways, and clearways.

Landing Performance Calculations and LDA

Landing Distance Required (LDR):

• Calculate using Aircraft Flight Manual (AFM) data.
• Adjust for weight, wind, runway condition, slope, and temperature.
• Multiply by regulatory safety factor (e.g., 1.67 for FAA Part 121).

Rule:
The factored LDR must not exceed the published LDA.

LDA and Takeoff Performance: Declared Distances in Balance

• Takeoff: Use TORA, TODA, and ASDA for takeoff calculations.
• Landing: Use LDA only.
• Balanced Field Length: The most restrictive declared distance governs maximum allowable weight and performance.

Case Studies

Teterboro (KTEB)

Physical runway: 7,000 ft
ASDA: 6,090 ft (due to safety areas)
LDA may be less than 7,000 ft if threshold is displaced. Always use published LDA.

Brown Field Municipal (SDM)

Runway 26R LDA: 7,932 ft (40 ft less than physical length due to ROFA encroachment). Even small reductions matter for large aircraft.

Factored Landing Distance and Safety Margins

• Factored Distance: Actual landing distance × regulatory safety factor (e.g., 1.67).
• Purpose: Provides margin for operational variability and ensures safe stopping.
• Requirement: The factored distance must be ≤ LDA.

Risks, Safety Margins, and Data Accuracy

• Runway Excursions: Most common landing incident; often due to overestimating LDA or failing to account for displaced thresholds or contamination.
• Data Verification: Always use current, official data—never rely on estimates or outdated charts.

Conclusion

Landing Distance Available (LDA) is a cornerstone of safe, compliant, and efficient airport and flight operations. Its correct determination, publication, and use are vital in preventing runway excursions, optimizing performance, and ensuring regulatory compliance. Understanding LDA’s relationship to other declared distances, as well as the technical and regulatory context in which it is applied, is essential for all aviation professionals.

Key Takeaway:
Always use the published LDA, apply regulatory safety margins, and verify data from official sources before every landing.

Further Reading

• ICAO Annex 14 – Aerodrome Design and Operations
• FAA Advisory Circular AC 150/5300-13B – Airport Design
• EASA CS-ADR-DSN – Aerodrome Design
• Aircraft Flight Manual (AFM) landing performance charts

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