Landing Distance Available (LDA): Runway Length for Aircraft Landings

Landing Distance Available (LDA) is a cornerstone concept in airport planning, aircraft operations, and aviation safety. It represents the declared runway length available for an aircraft’s landing roll—measured from the landing threshold to the end of the runway surface. Understanding LDA is essential for airport managers, pilots, dispatchers, and anyone involved in aviation infrastructure or flight operations.

Deep Dive: What is Landing Distance Available (LDA)?

Landing Distance Available (LDA) is the specific portion of a runway, as declared by the airport authority, that a landing aircraft is authorized to use for ground deceleration after touchdown. It’s measured from the runway’s landing threshold (the point where landing is permitted) to the far end of the runway surface.

This figure is not arbitrary: it’s determined by careful assessment of obstacles, pavement strength, and compliance with international standards such as ICAO Annex 14, FAA AC 150/5300-13A, and EASA CS-ADR-DSN. The LDA value is published in official sources (AIP, FAA Chart Supplement, airport charts), ensuring that pilots and operators have access to accurate, legally binding information.

Why LDA Matters

• Safety: Ensures aircraft have enough distance to decelerate and stop, preventing overruns.
• Flight Planning: Determines which runways are suitable for specific aircraft under current conditions.
• Regulatory Compliance: Operators must use LDA (not total runway length) for landing performance calculations, as required by FAA, EASA, and ICAO.
• Operational Efficiency: Accurate LDA values help optimize runway use and aircraft scheduling.

Depiction of runway declared distances including LDA, TORA, TODA, and ASDA. Source: Skybrary

Declared Runway Distances: LDA, TORA, TODA, ASDA

A runway’s usability is defined by four standardized “declared distances”:

Each distance serves a unique purpose. Using the wrong value, such as TORA instead of LDA for landing calculations, can result in unsafe operations.

How LDA is Determined and Published

Physical and Regulatory Foundations

• Obstacles: If objects (trees, buildings, terrain) penetrate protected approach surfaces, the landing threshold is displaced farther from the runway end, reducing LDA.
• Displaced Thresholds: The area before a displaced threshold is not available for landing touchdown and is excluded from LDA.
• Runway End Safety Areas (RESA)/Stopways: These are not included in LDA, as they are not designed for landing deceleration.

Measurement: LDA is always measured from the designated landing threshold to the end of the usable runway surface.

Publication

• Aeronautical Information Publication (AIP): Official source for all declared distances in each country.
• FAA Chart Supplement: U.S. authoritative source, updated every 56 days.
• Airport Charts: Declared distances are shown on diagrams with graphical and tabular data.
• EFBs & FMS: Electronic flight planning tools and onboard databases integrate these values.
• NOTAMs: Temporary reductions or changes to LDA are published as Notices to Airmen.

A runway with a displaced threshold. The area before the threshold is not available for landing and is excluded from LDA calculations.

Displaced Thresholds and Obstacles: Their Impact on LDA

Displaced thresholds are common causes for reduced LDA. These are points moved down the runway from the end to ensure obstacle clearance, noise abatement, or pavement requirements. The area before a displaced threshold, while sometimes used for takeoff or rollout in the opposite direction, cannot be used for landing touchdown in the affected direction.

Example:
A 3,000-meter runway with a 300-meter displaced threshold offers an LDA of only 2,700 meters for landing from that direction.

Displaced threshold marked with white arrows; area not available for landing.

Runway Safety Areas and Stopways: Not Part of LDA

• Runway Safety Areas (RSAs): Cleared zones beyond runway ends for overrun protection, not suitable for high-speed landing deceleration—thus excluded from LDA.
• Stopways: Paved or prepared areas for rejected takeoff extensions (ASDA), not for landing rollout. Pilots must avoid including these in landing calculations.

Charting, Data Sources, and Cross-Verification

• AIP and FAA Chart Supplement: Primary sources for official LDA values.
• Airport Diagrams: Show declared distances and displaced thresholds.
• EFBs & FMS: Integrate published LDA values, but must be kept current.
• NOTAMs: Provide temporary LDA changes.
• Best Practice: Cross-check LDA in multiple sources; use the most restrictive value if in doubt.

FAA airport diagram showing declared distances, including LDA, for each runway direction.

LDA in Flight and Airport Operations

Landing Performance Calculations:
Pilots and dispatchers must verify that the aircraft can land and stop within LDA, adjusting for weight, weather, surface conditions, and regulatory safety factors.

• FAA (Part 121/135): U.S. airlines must show the aircraft can land within 60% of LDA, factoring in forecast conditions.
• EASA/ICAO: Apply safety factors (1.67 dry, 1.92 wet) to actual landing distance, comparing to LDA.

In-Flight Updates:
Pilots must recalculate landing performance if runway conditions or LDA change due to construction, NOTAMs, or contamination.

Use Case Example:
If LDA for runway 27 is 6,200 feet due to an 800-foot displaced threshold, and a Boeing 737 requires 6,000 feet after adjustments, landing is legal and safe. If LDA drops to 5,800 feet (e.g., by construction), the landing becomes unsafe and non-compliant.

Factors Affecting Landing Distance and LDA Utilization

Runway Condition:
Contaminated (wet, icy, snowy) runways increase required landing distance. Pilots must use corrected performance data and compare to LDA.

Aircraft Weight & Configuration:
Heavier weights and certain flap settings increase landing roll.

Wind & Slope:
Tailwinds and uphill slopes increase required distance; headwinds and downhill slopes reduce it.

Environmental Factors:
Temperature, pressure altitude, and braking action reports all affect landing distance calculations.

Regulatory Safety Margins:
Mandated to ensure an extra buffer beyond the calculated landing roll.

Key Points for Airport Planners, Pilots, and Operators

• LDA is the only portion of the runway usable for landing deceleration, measured from threshold to runway end.
• Excludes areas before displaced thresholds, stopways, and safety zones.
• Always use published, current LDA values from authoritative sources.
• Factor in all operational and environmental variables in landing performance calculations.
• Stay informed of temporary LDA changes via NOTAMs.

Landing Distance Available (LDA) is a vital parameter underpinning safe, compliant, and efficient airport and flight operations. Understanding and applying LDA correctly is fundamental for everyone in the aviation ecosystem—from planners and engineers to pilots, dispatchers, and safety managers.