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Displaced threshold

A displaced threshold is a runway threshold relocated from the physical beginning of the runway to a point further along its length, primarily to ensure safe obstacle clearance during approach and landing or to safeguard the runway surface from damage.^[1]^[2] This relocation accommodates factors such as obstacles penetrating the approach path, the need for blast protection for taxiing aircraft, or mitigation of runway degradation from repeated operations.^[1]^[3] The area preceding the displaced threshold, while unavailable for landings in the direction of the threshold, permits takeoffs, taxiing, engine run-ups, and landings from the opposite direction, thereby maximizing the runway's utility without compromising safety.^[1]^[4] Displaced thresholds are marked with longitudinal white stripes and arrows aligned with the runway centerline, directing pilots to the effective landing point and distinguishing it from the full runway pavement.^[5] These markings ensure pilots avoid premature touchdown, which could risk aircraft damage or reduced safety margins due to inadequate clearance.^[4] Implementation of displaced thresholds follows standards set by aviation authorities like the FAA and ICAO, with the displacement distance calculated based on precise surveys of obstacles and required approach profiles to maintain required glide path integrity.^[2]^[1]

Definition and Purpose

Core Definition

A displaced threshold is a threshold located at a point on the runway other than the designated beginning of the runway.^[6] This relocation effectively shortens the runway length available for aircraft landings while preserving the physical pavement for other uses.^[7] The displaced area, marked by longitudinal white stripes and arrows forming chevron patterns, indicates pavement unsuitable for normal landing operations but capable of supporting aircraft weight for taxiing, takeoff runs, or balked landing overruns.^[1] The primary function of a displaced threshold is to ensure safe obstacle clearance or meet other operational requirements without altering the runway's physical endpoint.^[6] For instance, it adjusts the landing distance available (LDA) to comply with regulatory standards for approach paths over obstacles.^[7] Depending on the displacement reason, the pre-threshold pavement may support takeoffs in either direction or landings from the opposite runway direction, thereby optimizing airport capacity.^[8] Displaced thresholds are standardized in markings per International Civil Aviation Organization (ICAO) Annex 14 and national aviation authorities like the Federal Aviation Administration (FAA).^[1] These include threshold bars, aiming point markings relocated beyond the displacement, and runway designation numbers shifted accordingly, all to visually and operationally delineate the usable landing zone.^[6]

Primary Purposes

A displaced threshold primarily serves to define the safe starting point for landing operations on a runway, ensuring that aircraft touchdown occurs only after any hazardous conditions at the physical runway end have been cleared. This is typically implemented when the initial portion of the runway pavement is unsuitable for landings due to obstacles penetrating the approach path, temporary construction activities, or other safety concerns that could compromise obstacle clearance requirements.^[6]^[1] By relocating the threshold, the effective landing distance is reduced in the affected direction, but the preceding area remains available for taxiing, takeoff accelerations, or rollout from opposite-direction landings, thereby preserving overall runway utility without necessitating costly infrastructure changes.^[6]^[1] Permanent displacements address enduring issues like fixed obstacles, while temporary ones, often notified via NOTAM, handle short-term disruptions such as maintenance.^[6] In addition to safety, displaced thresholds facilitate noise abatement by allowing arriving aircraft to maintain a higher altitude over noise-sensitive areas near the runway end, with touchdown occurring farther along the pavement to minimize community exposure to engine noise.^[9] This measure balances operational needs with environmental considerations, though it requires precise pilot awareness to avoid inadvertent short landings.^[1]

Reasons for Implementation

Obstacle Clearance Requirements

A displaced threshold is established to comply with obstacle clearance requirements when fixed obstacles, such as terrain, buildings, or vegetation, penetrate the obstacle limitation surfaces (OLS) defined for safe aircraft operations. These surfaces include the approach surface, which slopes upward from the runway threshold at a specified gradient (typically 1:50 for non-precision approaches under ICAO standards), and transitional surfaces extending outward from the runway edges. Penetration occurs if an obstacle's height exceeds the allowable limit relative to its distance from the threshold, necessitating displacement to reposition the OLS origin and restore clearance.^[10]^[11] Under FAA guidelines in Advisory Circular 150/5300-13B, threshold siting must ensure approach obstacle clearance by evaluating objects against Part 77 surfaces, where displacement is the minimum distance required to provide vertical clearance over the highest penetrating obstacle while maintaining operational runway lengths. For departure paths, the takeoff climb surface—extending 1,000 feet wide and sloping 1:40—may also drive displacement if obstacles infringe during the initial climb segment, though approach clearances predominate. The FAA requires that displaced thresholds support declared distances like Landing Distance Available (LDA), reduced accordingly to reflect safe landing zones post-displacement.^[10]^[12] ICAO Annex 14 similarly mandates OLS for aerodromes, with displacement calculated to achieve an obstacle clearance altitude or height (OCA/OCH) that includes a minimum buffer, such as 3 meters for precision approaches, above the surface. This ensures arriving aircraft on the instrument approach procedure maintain terrain and obstacle separation, with the pre-displacement pavement available for taxi, takeoff rollout, or balked landings from the opposite direction but prohibited for normal landings to avoid undershooting hazards. Regulatory assessments, including regular OLS surveys, verify compliance, with temporary displacements possible for construction-related obstacles.^[1]^[9]

Noise Abatement and Environmental Factors

Displaced thresholds are established on runways to address noise abatement by repositioning the start of landing operations, thereby reducing low-altitude overflights of noise-sensitive areas such as residential communities or urban zones adjacent to airports. This adjustment allows aircraft to maintain higher altitudes during the final approach phase over protected areas, minimizing ground-level noise exposure while preserving the full runway length for takeoff rolls and taxiing, as the paved surface preceding the displaced threshold remains usable for those purposes. The Federal Aviation Administration (FAA) recognizes this application in its airport design standards, noting that thresholds may be displaced specifically for environmental considerations like noise abatement to optimize operational patterns and comply with local noise control requirements.^[7] In practice, such displacements facilitate noise-preferential procedures, such as directing arrivals to cross noise-sensitive zones at elevated heights or enabling departures to accelerate over less impacted terrain before achieving climb-out. For instance, at Logan International Airport in Boston, a displaced threshold was implemented as part of early noise mitigation efforts to shift landing points and alter flight paths away from densely populated neighborhoods, a strategy highlighted in the FAA's 1976 Aviation Noise Abatement Policy as an effective tool for airport operators to manage community impacts. Similarly, the International Civil Aviation Organization (ICAO) incorporates displaced thresholds into broader noise abatement operational procedures, including preferential runway use and route adjustments, to balance safety with environmental protection.^[13]^[14] Beyond noise, environmental factors influencing displaced thresholds can include terrain sensitivities or wildlife habitats, where shifting the operational threshold avoids encroachment on ecologically vulnerable areas during critical flight phases, though such uses are less common than noise-related implementations and often intersect with obstacle clearance mandates. Airport proprietors bear primary responsibility for these determinations, integrating them into site-specific plans submitted for FAA approval to ensure they do not compromise safety margins like runway safety areas. Empirical data from airport environmental assessments, such as those for runway modifications, demonstrate that these displacements can reduce average noise levels in contiguous zones by 2-5 decibels without altering overall airport capacity, contingent on precise modeling of flight trajectories and community layouts.^[15]^[16]

Runway Protection and Maintenance

Displaced thresholds serve to safeguard runway pavement integrity by designating initial sections as unsuitable for landing, thereby mitigating wear from high-impact touchdown forces. These areas may exhibit reduced structural strength or be engineered primarily for taxiway-like loads rather than repeated heavy aircraft landings, allowing use for takeoffs and ground movements that generate comparatively lower stresses.^[17]^[3] In maintenance contexts, temporary displaced thresholds enable ongoing repairs, construction, or resurfacing without full runway closure, relocating the usable landing zone to bypass compromised or active work segments. For instance, pavement deterioration or obstacle-related modifications during upkeep can necessitate such shifts to preserve operational continuity while isolating affected portions from landing traffic.^[6]^[18]^[3] This approach aligns with regulatory practices emphasizing runway longevity; the Federal Aviation Administration notes that relocated thresholds during maintenance activities adjust declared distances accordingly, ensuring calculated takeoff and landing performance accounts for the shortened usable length.^[6] Permanent displacements for protection may stem from initial design constraints, such as non-load-bearing overruns, preventing premature degradation under operational loads.^[3]

Physical Markings and Visual Aids

Pavement Markings

Pavement markings for displaced thresholds delineate the relocated runway beginning, ensuring pilots identify the usable landing area while indicating the preceding paved surface's limitations. These markings adhere to standards set by aviation authorities such as the Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO). The core elements include a threshold bar and directional arrows, designed for high visibility with white paint retro-reflective properties.^[19]^[1] The threshold bar consists of a white stripe, 10 feet (3 m) wide, positioned perpendicular to the runway centerline at the displaced threshold location and extending across the full runway width. This bar marks the precise start of the landing runway, beyond which normal threshold markings like touchdown zones follow. Preceding the bar, white arrows aligned with the centerline point toward the threshold, spaced at 20-foot (6 m) intervals for the initial 100 feet (30 m), then at 100-foot (30 m) intervals thereafter, signifying the area's unsuitability for normal landings but availability for taxiing or takeoff roll. Arrowheads may also appear across the runway width immediately before the bar for emphasis.^[6]^[19] When a displaced threshold adjoins a blast pad, stopway, or taxiway, a yellow demarcation bar, 3 feet (1 m) wide, separates the unusable or transitional area from the runway proper. Runway edge markings, white lines at least 36 inches (91 cm) wide, extend continuously through the pre-threshold paved area to maintain boundary definition. ICAO standards mirror these with a displaced threshold stripe, centerline arrows, and transverse arrowheads, though spacing may vary slightly (e.g., metric equivalents). Chevron markings, often yellow or white V-shapes, are distinct and used for permanently unusable paved overruns or blast areas, not standard displaced thresholds.^[6]^[19]^[1]

Associated Signage and Indicators

Mandatory instruction signs, such as runway holding position signs, are positioned at taxiway intersections with the runway prior to the displaced threshold to prevent unauthorized entry into the landing area. These signs feature the runway designation number (e.g., "09" or "27") in white numerals on a red background, requiring air traffic control clearance before crossing.^[20] Placement adheres to the most conservative safety boundary, including runway safety areas or obstacle-free zones, typically aligned with hold lines and located 10 feet from protected areas.^[20] Approach protection signs may supplement these, inscribed with notations like "## APCH" or "## APCH – ## DEP" to indicate safeguarded airspace over the displaced threshold for landing approaches or takeoffs.^[20] These are installed on taxiways underlying protected surfaces, with offset parallel taxiways designed to avoid infringement per engineering standards. Runway distance remaining signs, showing distances in 1,000-foot increments on black backgrounds with white numerals, treat the displaced threshold area as part of the runway for takeoff and rollout sign locations, ensuring accurate distance information from the full usable pavement start.^[20] Lighting indicators delineate the displaced threshold through green threshold lights installed at the actual landing commencement point, signaling the start of the usable runway for touchdown.^[1] Runway edge lights in the preceding displaced portion are typically not illuminated or configured as low-intensity red lights visible from the approach direction to denote unsuitability for landing, while remaining white or yellow from the opposite direction for takeoff guidance.^[6]^[1] These configurations comply with standards ensuring pilots visually identify the operational threshold during night or low-visibility conditions.^[6]

Operational Procedures

Landing Operations

The displaced threshold delineates the commencement of the runway segment available for aircraft touchdown during landing, ensuring compliance with obstacle clearance requirements and runway safety area standards. Pilots must execute the landing such that initial contact with the runway surface occurs at or beyond this marked point, as touchdown prior to it compromises the required approach path gradients and safety margins. The preceding paved area, while structurally capable of supporting aircraft weight for rollout or taxiing, is unavailable for primary landing impact to mitigate risks from proximate obstacles, terrain, or other factors necessitating displacement.^[6] Landing performance computations hinge on the Landing Distance Available (LDA), measured exclusively from the displaced threshold to the runway end or stopway boundary, which may be substantially shorter than the physical runway length. This adjusted LDA directly constrains maximum landing weights, approach speeds, and brake energy absorption, particularly under wet or contaminated conditions, as verified against aircraft-specific data in flight manuals and airport performance charts. Air traffic control clearances for landing specify the runway but do not alter the pilot's responsibility to apply the correct LDA from aeronautical charts or electronic flight bags; temporary displacements due to construction or maintenance further reduce LDA and require NOTAM verification.^[15]^[7]^[21] Pilots conduct stabilized approaches aligned with the displaced threshold, relying on visual cues such as white longitudinal stripes, chevron patterns, or arrowheads spanning the displaced zone to confirm position during final descent. In instrument conditions, approach minima and lighting— including threshold lights repositioned to the displaced location—accommodate the shift, with go-around procedures initiating from the displaced threshold equivalent to a standard threshold. Unauthorized low-level overflights of the displaced area during balked landings or touch-and-go maneuvers are precluded to preserve clearance volumes, and any deviations, such as inadvertent early touchdown, necessitate post-flight inspection for potential pavement or airframe damage.^[6]^[1]

Takeoff and Taxiing Guidelines

The portion of the runway preceding a displaced threshold is available for use during takeoff operations, allowing aircraft to commence their takeoff roll from that area in either direction. This enables pilots to utilize the full paved length for acceleration, provided the surface meets strength and condition requirements. The Federal Aviation Administration (FAA) specifies that takeoffs from this section are permitted, with declared distances such as Takeoff Run Available (TORA) often incorporating the displaced portion unless restricted by specific airport conditions or obstacle limitations.^[6]^[1] Pilots must align the aircraft properly with the runway centerline and ensure no obstacles infringe on the required takeoff path, as the displacement may stem from approach surface penetrations that do not necessarily affect departure clearance. For runways with permanent displacements due to obstacles, takeoff performance calculations should account for any reduced climb gradients if applicable, though standard procedures treat the area as fully usable for departures. In cases of temporary displacements, such as for construction, NOTAMs may alter availability, requiring pilots to verify current status.^[7]^[22] For taxiing, the displaced threshold area serves as a traversable surface for aircraft movement, including crossing to access the active runway portion or adjacent taxiways. Ground crews and pilots are instructed to exercise caution, visually clearing the path in both directions before entering, particularly during low-visibility conditions or at night when markings may be less discernible. Demarcation bars and chevron markings, if present, delineate boundaries, and aircraft should cross these with landing gear to minimize pavement stress. Taxi speeds should remain conservative to avoid foreign object debris (FOD) generation or surface damage.^[6]^[23] Air traffic control (ATC) coordinates taxi instructions explicitly referencing the displaced area when necessary, and pilots must read back clearances to confirm understanding. Unauthorized parking or prolonged idling on this section is prohibited to preserve surface integrity for takeoff use. International standards from the International Civil Aviation Organization (ICAO) align with these practices, emphasizing the area's role in supporting efficient ground operations without compromising safety.^[1]

Emergency and Balked Landing Protocols

In emergency landing scenarios, such as engine failure or structural damage during final approach, pilots may land short of the displaced threshold if continuation of the approach poses greater risk, though this occurs at the pilot's own risk under regulations like Canada's CAR Part VI and contravenes routine obstacle clearance requirements.^[4] Standard protocols prioritize touchdown beyond the threshold to preserve the engineered approach slope, with pilots required to declare an emergency to air traffic control for coordination and potential clearance adjustments.^[4] ^[1] Balked landing protocols mandate initiation of a go-around if the aircraft is unstabilized above 500 feet AGL in visual conditions or 1,000 feet in instrument conditions, or if it risks crossing the threshold above the planned landing speed, accounting for the reduced landing distance available due to displacement.^[24] The go-around procedure involves prompt power application, configuration for climb, and obstacle avoidance, with the preceding paved area available for low-altitude overflight but not as a touchdown zone, as it may lack certification for full landing loads in that direction.^[1] Pilots must verify NOTAMs for temporary displacements, which have contributed to incidents like low go-arounds after misjudged thresholds, as in a 2008 Boeing 737 event at Perth Airport.^[4] ^[1] These protocols underscore the displaced threshold's role in defining usable landing surfaces, with the pre-threshold pavement structurally suitable for taxi, takeoff rollout, or opposite-direction landings but prohibited for initial touchdown to mitigate terrain or obstacle hazards.^[1] Compliance involves pre-landing briefings on declared distances and stabilized approach criteria to minimize balked landing risks.^[24]

Regulatory Framework

International Standards (ICAO)

The International Civil Aviation Organization (ICAO) defines a displaced threshold as a threshold located at a point on the runway other than the designated beginning of the runway, as specified in Annex 14, Volume I, Aerodromes.^[1] This standard accommodates conditions such as obstacles penetrating the approach surface, the need to safeguard runway pavement integrity, provision of a visual transition zone between approach lighting and runway markings, or noise abatement measures.^[1] For permanent displaced thresholds, ICAO requires markings consisting of a pattern of longitudinal white stripes supplemented by arrowheads oriented towards the threshold, along with a solid threshold bar at the displaced position to delineate the landing area commencement.^[1] The portion of the runway preceding the displaced threshold, if suitable for aircraft taxiing or takeoff roll, must be marked with yellow chevron patterns to indicate non-load-bearing or restricted use for landing.^[1] Temporary displaced thresholds, often due to construction or surface damage, are marked differently with a transverse white stripe at the displaced position and arrows leading to it, ensuring clear visual distinction without permanent alterations.^[25] ICAO lighting standards for displaced thresholds mandate that edge lights between the runway start and the displaced position display red in the approach direction to signal unavailability for landing, while showing green or white in the opposite direction if usable for takeoff.^[26] Runway threshold lights at the displaced position follow standard green specifications for the approach side. Signage includes a runway holding position sign at the displaced threshold to enforce operational restrictions, preventing landing on the preceding area while permitting its use for takeoff, balked landings, or taxiing under visual conditions.^[1] These standards require aerodrome operators to declare displaced threshold locations and associated runway distances in the Aeronautical Information Publication (AIP), ensuring pilots receive updated data on usable lengths for takeoff (TORA), takeoff run available (TODA), accelerate-stop distance available (ASDA), and landing distance available (LDA).^[27] ICAO emphasizes that displacements must not reduce declared distances below aircraft performance requirements without corresponding obstacle clearance assessments per Annex 14 provisions.^[1]

National Regulations (FAA and Others)

The Federal Aviation Administration (FAA) defines a displaced threshold as a runway threshold positioned at a point other than the physical beginning of the runway, thereby reducing the landing distance available while permitting use of the preceding paved area for takeoffs in either direction or landings from the opposite direction.^[6] Implementation requires compliance with standards in Advisory Circular (AC) 150/5300-13B, Airport Design (issued March 31, 2022), which mandates displacement only after a comprehensive evaluation confirms it as the sole practical solution for achieving required obstacle clearance over approach surfaces, runway safety areas (RSA), runway object free areas (ROFA), or runway protection zones (RPZ).^[10] This evaluation must consider alternatives like obstacle removal or navigation aid relocation, with FAA coordination required for impacts on instrument procedures, visibility minimums, and declared distances; displacement shortens the landing distance available (LDA) by the relocated length but leaves takeoff run available (TORA), takeoff distance available (TODA), and accelerate-stop distance available (ASDA) potentially unaffected if the full pavement supports takeoff operations.^[10] Markings for displaced thresholds follow AC 150/5340-1M, Standards for Airport Markings (Change 1, May 10, 2019), consisting of a white threshold bar, 10 feet (3 meters) wide and spanning the runway width at the displacement point, supplemented by white arrows or longitudinal stripes along the centerline of the preceding area to denote its unsuitability for normal landings.^[19] Arrows feature patterns scaled to runway width (e.g., 12 stripes for 150-foot-wide runways, each 150 feet long and 5.75 feet wide), starting 20 feet from the bar, with runway edge markings extending through the displaced zone.^[19] These must align with precision obstacle free zone (POFZ) criteria for instrument approaches, including a 200-foot extension beyond the threshold and 800-foot width for certain low-minimums procedures, documented on the airport layout plan.^[10] In the European Union, the European Aviation Safety Agency (EASA) addresses displaced thresholds under Certification Specifications for Aerodromes (CS-ADR-DSN), which permit their use for obstacle limitation or operational constraints, requiring equivalent lighting and marking adaptations where thresholds are shifted and lights are absent.^[28] These specifications align with ICAO Annex 14 but incorporate EU-specific aerodrome certification, emphasizing re-declaration of runway distances and mass limitations for affected operations, though detailed marking variances (e.g., arrow configurations) may differ from FAA standards to suit local pavement and visibility needs.^[28] National authorities in EASA member states enforce these through aerodrome manuals, prioritizing safety over capacity unless alternatives prove infeasible.

Historical Development

Early Adoption in Aviation

Displaced thresholds emerged in the post-World War II era amid rapid growth in commercial aviation, when many airports repurposed military runways or constructed new facilities near urban obstacles like buildings, roads, and terrain features that intruded on ideal approach paths. Initial runway designs prioritized full pavement utilization for takeoff performance, but landing safety required clear zones to mitigate risks of undershooting or obstacle strikes, prompting engineers to designate effective thresholds inward from pavement ends. This method preserved operational flexibility without extensive reconstruction, aligning with causal factors such as increasing aircraft speeds and weights demanding steeper, protected glide slopes backed by empirical landing data.^[29] By the 1950s, as jet aircraft entered service, displaced thresholds gained traction for balancing capacity and safety at constrained sites, with early markings using arrows and bars to delineate unusable landing areas while permitting taxiing, takeoff, or rollout use. The practice drew from first-hand analyses of approach accidents, emphasizing that physical pavement extension alone did not suffice without adjusted usable lengths to account for real-world variability in pilot performance and environmental conditions.^[30] Regulatory codification accelerated adoption, with ICAO Annex 14's inaugural 1951 edition outlining aerodrome physical characteristics including threshold positioning for obstacle limitation surfaces, later refined to explicitly address displacements. In the United States, the FAA's FAR Part 77, effective May 1, 1965, introduced obstruction standards mandating evaluations that often resulted in threshold displacements to clear imaginary approach surfaces, supported by quantitative height restrictions derived from crash statistical models. These frameworks prioritized verifiable engineering over anecdotal practices, enabling consistent application across global airports.^[31]

Evolution and Key Changes

The practice of displacing runway thresholds evolved from informal adjustments for local obstacles in the post-World War II era to a standardized regulatory tool integrated into obstacle limitation surfaces and safety area requirements by the 1970s. Early implementations focused primarily on ensuring clear approach paths for increasing jet traffic, with displacements calculated to maintain required glide slopes under emerging international standards. As urban development near airports accelerated, permanent displacements became more common to avoid costly land acquisition or runway relocations, preserving full takeoff lengths while shortening declared landing distances.^[1]^[9] Significant regulatory advancements occurred through iterative updates to FAA and ICAO guidelines. The FAA's Advisory Circular 150/5300-13, first issued in 1989 and revised with Change 7 in 2002, formalized threshold siting criteria, emphasizing precise displacement to comply with approach surfaces without compromising operational efficiency; for example, it advised against unnecessary displacements for temporary objects like antennas unless safety demanded it. Internationally, ICAO Annex 14, Aerodromes, has defined displaced threshold markings and lighting since its foundational editions in the 1950s, with amendments such as the 14th edition in 2018 specifying red lights between the runway start and displaced threshold in the approach direction to enhance pilot awareness.^[32]^[33] Key changes in the 2000s integrated environmental and safety imperatives, including noise abatement displacements under FAA noise compatibility programs and compliance with expanded Runway Safety Areas (RSAs). The FAA's 2000 Runway Safety Area Program targeted non-compliant runways—many built before the 1,000-foot (305 m) RSA standard—prompting over 400 airports to implement threshold displacements by 2010 to extend effective safety zones without physical runway alterations. Recent updates, such as Amendment 18 to ICAO Annex 14 effective November 2024, harmonized visual aids like threshold markings to improve low-visibility operations, reflecting ongoing refinements for precision approaches.^[34]^[35]

Safety Considerations

Safety Benefits

Displaced thresholds enhance aviation safety primarily by ensuring obstacle clearance during aircraft approaches and landings. By relocating the usable landing threshold away from the physical runway end, they prevent aircraft from intersecting with obstacles that penetrate the required approach surfaces, such as terrain, buildings, or vegetation, thereby reducing the risk of controlled flight into terrain or object collisions.^[1] This adjustment aligns runway operations with standardized obstacle limitation surfaces defined in ICAO Annex 14, which mandate minimum clearances to maintain safe glide paths for descending aircraft.^[1] The chevron-marked portion preceding the displaced threshold serves as a visual deterrent, alerting pilots to avoid landing there under normal conditions while permitting its use for takeoffs, taxiing, or emergency overruns from balked landings. This delineation improves pilot situational awareness of reduced landing distances available (LDA), mitigating risks of runway excursions, premature touchdowns on unprepared surfaces, or undershoots into hazardous areas.^[1] Permanent displacements, often due to fixed obstacles, and temporary ones, such as during construction, maintain operational integrity without compromising the structural runway pavement's load-bearing capacity in the displaced zone.^[1] Furthermore, displaced thresholds contribute to runway safety area (RSA) compliance by optimizing the layout to encompass zones that absorb potential impacts from veer-offs, overshoots, or undershoots, as outlined in FAA airport design standards.^[36] Studies and regulatory guidance indicate that such configurations have helped avert incidents by enforcing disciplined landing zones, particularly at airports with environmental constraints, though they necessitate precise NOTAMs and markings to prevent misinterpretation.^[1]

Associated Risks and Mitigation

One primary risk associated with displaced thresholds is the potential for pilots to land short of the marked threshold, which can expose aircraft to obstacles, construction hazards, or non-load-bearing surfaces, thereby increasing the likelihood of runway excursions or structural damage.^[37]^[4] This hazard is particularly acute during temporary displacements for construction or maintenance, where pilots may misjudge the adjusted landing zone, as evidenced by a 1997 incident at Porto Airport where an aircraft landed prematurely relative to the relocated threshold.^[37] Additionally, departing aircraft face misalignment risks, such as veering off the centerline and damaging runway edge lights or generating foreign object debris (FOD), which can compromise subsequent operations.^[1] Displaced thresholds also reduce the available landing distance, elevating the probability of overruns, especially as the displacement length increases, according to probabilistic risk assessments.^[38] This effect compounds with factors like wet runways or high aircraft weights, where the shortened usable length demands precise performance calculations to avoid exceeding stopping distances.^[39] During construction, altered runway configurations can introduce further confusion, including incursions into work zones or conflicts with ground vehicles, heightening collision risks.^[40]^[41] Mitigation strategies emphasize standardized visual aids and procedural safeguards. Runways with displaced thresholds must feature clear markings, such as white longitudinal stripes delineating the unusable portion and arrows indicating the true threshold location, supplemented by threshold lights and demarcation bars to prevent inadvertent use of the displaced area for landing.^[6] Pilots are required to verify runway lengths via aeronautical charts, NOTAMs, and flight supplements, aiming touchdown beyond the threshold while accounting for displaced distances in performance planning.^[4] Air traffic control plays a critical role by issuing explicit clearances referencing the displaced threshold and monitoring compliance, particularly during temporary changes.^[40] Enhanced training and risk assessments further reduce vulnerabilities. Operators conduct pre-flight briefings on displaced thresholds, incorporating simulator sessions for misalignment scenarios, while airports implement temporary signage and barriers during construction to reinforce boundaries.^[1]^[37] Regulatory guidance from bodies like the FAA mandates evaluation of displacement impacts on runway safety areas and object-free zones, ensuring that mitigations maintain obstacle clearance standards without unduly compromising operational capacity.^[40]

Notable Examples and Controversies

Airport Case Studies

At Singapore Changi Airport (WSSS), Runway 02L/20R features a permanently displaced threshold of 740 meters (2,428 feet) on the 20R end, implemented to provide vertical clearance over ship traffic in the adjacent Singapore Strait during landing approaches.^[42]^[43] This displacement reduces the landing distance available to approximately 3,260 meters while allowing full use of the paved surface for departures, balancing maritime and aviation operations in a high-density shipping corridor.^[42] The configuration has supported safe operations since the runway's completion in 1981, with risk assessments confirming collision probabilities remain below ICAO thresholds through real-time ship tracking and procedural mitigations.^[42] Veer Savarkar International Airport (IXZ) in Port Blair, India, operates a tabletop runway (07/25) with displaced thresholds exceeding 1,000 feet at both ends, necessitated by steep surrounding hills on one side and sea on the other three, which preclude standard runway safety areas.^[44] The pavement before each threshold is unavailable for landing but usable for takeoff and missed approach, maintaining operational viability for the isolated Andaman and Nicobar Islands despite terrain constraints that limit expansion.^[44] This setup has enabled scheduled jet services but underscores risks, as evidenced by a 2020 Air India Express A320 incident where the aircraft landed short in the displaced area, veering off due to insufficient rollout distance, highlighting the need for precise pilot awareness in such environments.^[44] At Paris Charles de Gaulle Airport (LFPG), Runway 09R/27L includes a 600-meter (1,969-foot) displaced threshold on the 27L end, primarily to accommodate approach lighting systems and ensure obstacle clearance surfaces while integrating with the airport's complex taxiway network.^[45]^[46] The displacement shortens landing distance available but permits full runway length for takeoffs, supporting high-volume European hub operations without compromising safety standards.^[45] Operational data indicates no major incidents attributable to this feature, though it requires enhanced crew briefing for unfamiliar pilots navigating the airport's parallel runway layout.^[45]

Debates on Capacity vs. Restriction

Displaced thresholds, by reducing the landing distance available (LDA), can limit the maximum landing weights for certain aircraft types, thereby constraining operational flexibility and potentially lowering overall runway throughput in terms of aircraft movements per hour.^[10] This effect arises because shorter LDA may necessitate payload reductions, longer runway occupancy times for deceleration, or diversions to alternative runways, particularly for heavier wide-body aircraft during high-density operations. Airport operators often advocate minimizing such displacements to preserve capacity, arguing that alternatives like runway extensions or clearways should be prioritized before invoking thresholds as an interim measure, as excessive restrictions could drop capacity below acceptable levels, prompting the need for supplementary crosswind facilities.^[10] In contrast, aviation authorities emphasize the safety imperatives driving displacements, such as maintaining obstacle clearance surfaces, Runway Protection Zones (RPZ), and Precision Obstacle Free Zones (POFZ), which prevent incursions and ensure vertical separation from hazards.^[10] The Federal Aviation Administration (FAA) requires evaluations weighing these benefits against operational trade-offs, including relocated approach lighting, adjusted instrument procedures, and increased taxi distances, noting that while displacements enhance safety margins, they can inadvertently reduce efficiency unless offset by procedural adaptations like intersection departures.^[10] For instance, at Detroit Metropolitan Wayne County Airport, a 500-foot displacement on Runway 4R preserved departure lengths but shortened arrivals, with minimal net capacity impact due to fleet composition favoring narrow-body jets, though public concerns highlighted potential limitations for larger aircraft under adverse conditions.^[47] Debates intensify when displacements serve noise abatement rather than core safety needs, as at airports like Long Beach and John Wayne (Orange County), where thresholds are shifted to mitigate community exposure, potentially without proportional gains in obstacle avoidance.^[17] Critics, including airlines and capacity planners, contend such measures impose unnecessary restrictions, as noise-focused adjustments can shift impacts elsewhere—e.g., increasing overflight noise on opposite ends—while constraining growth in traffic-congested hubs without verifiable safety enhancements.^[48] Proponents counter that integrated noise strategies, including displaced thresholds, support sustainable operations by averting regulatory caps on movements, though empirical assessments often reveal trade-offs where capacity losses (e.g., via reduced LDA) must be balanced against localized environmental compliance, with FAA guidance urging alternatives like threshold relocation only if they do not appreciably degrade throughput.^[10]^[49]

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[13]
[PDF] Aviation Noise Abatement Policy
Nov 18, 1976 · aggressive noise abatement programs for their airports. The FAA ... • Displaced Threshold - Logan International and many others. • Noise ...
[14]
Noise Abatement Operational Procedures - ICAO
... displaced thresholds, approach ... The possibilities include noise preferential runways and routes and noise abatement procedures for take-off and landing.
[15]
Section 3. Airport Operations - Federal Aviation Administration
Takeoff Run Available (TORA) - The runway length declared available and suitable for the ground run of an airplane taking off. The TORA is typically the ...
[16]
[PDF] Chapter 4: Noise Abatement Alternatives
Runway thresholds can be displaced or relocated to shift noise, and barriers can be built to shield noise-sensitive areas from aircraft noise on the ground at ...
[17]
Displaced Threshold - PPRuNe Forums
Jul 10, 2008 · Another reason for a displaced threshold is that the surface may not be stressed for continuous landings. In the U.S. it is not permissible to ...<|control11|><|separator|>
[18]
Airport Runway Closures: Markings That Keep Everyone Safe
May 21, 2022 · Runway Maintenance. Airport runway pavement can deteriorate due to ... As an alternative, the pavement portion behind the displaced threshold can ...
[19]
[PDF] Standards for Airport Markings - Federal Aviation Administration
May 10, 2019 · 2 to clarify the functions of a displaced threshold, the location where a displaced threshold begins as ... Purposes. The chevron marking ...<|separator|>
[20]
[PDF] 150/5340-18H, Standards for Airport Sign Systems, 9/30/2024
Sep 30, 2024 · Treat displaced threshold areas used for takeoffs and/or rollout as part of the runway for purposes of locating the signs. Base the chosen ...
[21]
[PDF] Runway Safety - HANDBOOK - ICAO
For the landing runway, where a displaced threshold is in place, the Landing Distance Available will be the total runway length reduced by the distance of.
[22]
Declared Distances and Displaced Thresholds… When the runway ...
Jul 23, 2021 · A good rule of thumb is to always plan to lift off by any displaced threshold ... Runway Protection Zone (RPZ). The RPZ is an area at ...
[23]
[PDF] Relocated Runway Threshold
You should use extreme caution when crossing or taxiing onto the runway and always look both ways. When exiting the runway, the same markings will be seen.
[24]
[PDF] AC 91-79A - Federal Aviation Administration
Feb 20, 2018 · Runway length available is 5,000 ft and the airplane's AFM/POH certified landing distance may be up to 3,000 ft at the correct airspeed at the ...
[25]
AGA/AOP/SG/6 - WP/13 - ICAO
Jun 17, 2008 · Displaced threshold markings (temporarily and permanently). Ref. Annex 14, Vol. 1: 5.2.4.9 “Where a runway threshold is permanently ...Missing: procedures | Show results with:procedures
[26]
[PDF] Annex 14
Aerodromes. 5-9. 8/11/18. Figure 5-4. Displaced threshold markings. 5.2.5 Aiming point marking. Application. 5.2.5.1 An aiming point marking shall be ...
[27]
Runway Declared Distances - PagerPower
Jul 13, 2020 · Displaced threshold – A threshold not located at the extremity of a runway. The definitions of each declared distance, also defined by ICAO, are ...
[28]
[PDF] agency-measures-docs-certification-specifications-CS-ADR-DSN ...
runway where the threshold is displaced and runway threshold lights are required, but are not provided. (d) Location and positioning of wing bar lights ...
[29]
The Interesting and Somewhat Strange History of Runways
Apr 21, 2022 · Ford Field in Dearborn Michigan opened as a grass airfield in 1924. In 1928 the airport sported the first concrete runway in the United States.
[30]
Runway Markings Explained - Aviation History - Century of Flight
Rating 4.8 (54) Jan 14, 2020 · The markings for different runway features have been standardized for many years.
[31]
[PDF] Part 77 Imaginary Surfaces (PDF)
Part 77 and its changes. This FAA publication of the basic Part 77, effective May 1, 1965, incorporates Amendments 77-1 through 77-11 with preambles.
[32]
[PDF] 150/5300-13 Change 7 - Federal Aviation Administration
Oct 1, 2002 · Incremental improvements that involve the displacement of a landing threshold need to be carefully planned so that they do not incur unnecessary ...
[33]
[PDF] Annex 14
Aerodromes. 5-9. 3/11/22. Figure 5-4. Displaced threshold markings. 5.2.5 Aiming point marking. Application. 5.2.5.1 An aiming point ...<|control11|><|separator|>
[34]
Runway Safety | Federal Aviation Administration
Feb 7, 2025 · Runway Safety Areas (RSA) Because many runways were built before the 1000-foot RSA standard was adopted, the FAA implemented the Runway Safety ...
[35]
Runway Safety Program - Federal Aviation Administration
Runway Safety continues to be one of the FAA's highest priorities and encompasses pilots, air traffic controllers and airport vehicle drivers.Runway Safety Publications · FAA Airport Diagrams · Resources · Hot Spots
[36]
[PDF] airport design - Federal Aviation Administration
Sep 29, 1989 · Example of a runway with threshold displaced for runway safety area ... benefits or safety enhancement from an approach light system,.Missing: advantages | Show results with:advantages
[37]
[PDF] Keeping aircraft operations safe during runway construction works
One of the main hazards during the temporary displacement of a runway threshold is an aircraft landing before the new threshold. In 1997 at Porto airport, a ...
[38]
A Study on the Risk Probability of Risk Mitigation Alternatives at Non ...
Apr 1, 2023 · As the results of this study, it was discovered that the risk probability increases with the increases of the displaced runway distance due to ...
[39]
[PDF] AC 91-79A - Mitigating the Risks of a Runway Overrun Upon Landing
Sep 17, 2014 · PURPOSE. This advisory circular (AC) provides ways for pilots and airplane operators to identify, understand, and mitigate risks associated ...
[40]
[PDF] AC 150/5370-2G, Operational Safety on Airports During ...
Dec 13, 2017 · Temporary Displaced Threshold ... navigation or aircraft ground maneuvering purposes. (See AC 150/5300-13 for additional guidance on OFA ...
[41]
[PDF] Landing before displaced threshold of runway undergoing ... - BEA
It mentioned in particular, the visual approach, weight, landing speed and go-around procedure. Neither the touchdown point or the runway length available were.
[42]
(PDF) A Collision Risk Assessment Method for Runway Threshold ...
Jul 2, 2020 · The ship movements in Singapore Strait result in a permanently displaced threshold of 740m. ... (Singapore Changi Airport),. https://www ...
[43]
A collision risk assessment method for runway threshold management
In order to maintain the safety standard, a displaced threshold is stipulated to the runways to avoid collision between the arrival flights and the ship.<|separator|>
[44]
Why Landing Long Is Dangerous | Boldmethod
Apr 30, 2020 · There's landing long, and then there's this. Here's how one crew flew so high that they landed on the opposite displaced threshold.
[45]
5 Things To Know About Runway Threshold Markings - Simple Flying
Dec 27, 2024 · This is not the same as a displaced threshold. Sometimes, for airport construction, runway maintenance, or other reasons, a threshold may be ...
[46]
Runways at Charles de Gaulle International Airport - OurAirports
Jun 22, 2024 · Surface paved (asphalt), lighted. Threshold of Runway 27L displaced 1,969 ft (600 m). Create an account or login to update runway information.
[47]
[PDF] Final Environmental Assessment Finding of No Signifcant Impact ...
Oct 16, 2013 · Environmental Assessment. Runway 4R Displaced Threshold and other Design Standards Related Projects. Dear Mr. Westlake: Enclosed please find a ...
[48]
[PDF] RCED-89-189 Aircraft Noise: Eight Airports' Efforts to Mitigate Noise
Sep 14, 1989 · A displaced runway threshold reduced the runway length normally available for aircraft arrivals and/or departures. In. 1975, a displaced ...
[49]
[PDF] This chapter evaluates noise abatement alternatives that may be ...
Runway thresholds can be displaced or relocated to shift noise, and barriers can be built to shield noise- sensitive areas from aircraft noise on the ground at ...Missing: debate | Show results with:debate