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Landing of Hawker Sea Fury FB 10

Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing", "touchdown"a or "splashdown" as well. A normal aircraft flight would include several parts of flight including taxi, takeoff, climb, cruise, descent and landing.

An aircraft landing at Haneda Airport in Japan, 2021

Aircraft

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Aircraft usually land at an airport on a firm runway or helicopter landing pad, generally constructed of asphalt concrete, concrete, gravel or grass. Aircraft equipped with pontoons (floatplane) or with a boat hull-shaped fuselage (a flying boat) are able to land on water. Aircraft also sometimes use skis to land on snow or ice.

To land, the airspeed and the rate of descent are reduced such that the object descends at a low enough rate to allow for a gentle touch down. Landing is accomplished by slowing down and descending to the runway. This speed reduction is accomplished by reducing thrust and/or inducing a greater amount of drag using flaps, landing gear or speed brakes. When a fixed-wing aircraft approaches the ground, the pilot will move the control column back to execute a flare or round-out. This increases the angle of attack. Progressive movement of the control column back will allow the aircraft to settle onto the runway at minimum speed, landing on its main wheels first in the case of a tricycle gear aircraft or on all three wheels simultaneously in the case of a conventional landing gear-equipped aircraft, commonly referred to as a "taildragger".[1][2][3][4]

Light aircraft

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Piper Cherokee landing sequence from approach to flare

In a light aircraft, power is adjusted to control the descent rate, and pitch attitude is adjusted to control airspeed,[5] although theoretically they must be adjusted together.[6]

In a light aircraft, with little crosswind, the ideal landing is when contact with the ground occurs as the forward speed is reduced to the point where there is no longer sufficient airspeed to remain aloft. The stall warning is often heard just before landing, indicating that this speed and altitude have been reached. The result is very light touch down.[4]

Light aircraft landing situations, and the pilot skills required, can be divided into four types:

  • Normal landings[4]
  • Crosswind landings - where a significant wind not aligned with the landing area is a factor[4]
  • Short field landings - where the length of the landing area is a limiting factor[4]
  • Soft and unprepared field landings - where the landing area is wet, soft or has ground obstacles such as furrows or ruts to contend with[4]

Large aircraft

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A landing Delta Air Lines Boeing 767-400ER. The smoke emanating from the left main undercarriage wheels shows that it touched down on that main landing gear first, which is normal procedure in a left cross wind.

In large transport category (airliner) aircraft, pilots land the aircraft by "flying the airplane on to the runway."[citation needed] The airspeed and attitude (pitch angle) of the plane are adjusted for landing. Thrust and pitch must be adjusted together,[7] however the technique is reversed compared to light aircraft.[8] In large aircraft, thrust is used to control airspeed and pitch is used to control rate of descent.[9] The airspeed is kept well above stall speed and at a constant rate of descent. A flare is performed just before landing, and the descent rate is significantly reduced, causing a light touch down. Upon touchdown, spoilers (sometimes called "lift dumpers") are deployed to dramatically reduce the lift and transfer the aircraft's weight to its wheels, where mechanical braking, such as an autobrake system, can take effect. Reverse thrust is used by many jet aircraft to help slow down just after touch-down, redirecting engine exhaust forward instead of back. Some propeller-driven airplanes also have this feature, where the blades of the propeller are re-angled to push air forward instead of back using the 'beta range'.

Environmental factors

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Factors such as crosswind where the pilot will use a crab landing or a slip landing will cause pilots to land slightly faster and sometimes with different aircraft attitude to ensure a safe landing.

Other factors affecting a particular landing might include: the plane size, wind, weight, runway length, obstacles, ground effects, weather, runway altitude, air temperature, air pressure, air traffic control, visibility, avionics and the overall situation.

For example, landing a multi-engine turboprop military such as a C-130 Hercules, under fire in a grass field in a war zone, requires different skills and precautions than landing a single engine plane such as a Cessna 150 on a paved runway in uncontrolled airspace, which is different from landing an airliner such as an Airbus A380 at a major airport with air traffic control.

Required Navigation Performance (RNP) is being used more and more. Rather than using radio beacons, the airplane uses GPS-navigation for landing using this technique. This translates into a much more fluid ascent, which results in decreased noise, and decreased fuel consumption.[10]

Parachutes

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A drag chute is deployed by Space Shuttle Endeavour during landing

The term "landing" is also applied to people or objects descending to the ground using a parachute. Some consider these objects to be in a controlled descent instead of actually flying. Most parachutes work by capturing air, inducing enough drag that the falling object hits the ground at a relatively slow speed. There are many examples of parachutes in nature, including the seeds of a dandelion.

On the other hand, modern ram-air parachutes are essentially inflatable wings that operate in a gliding flight mode. Parachutists execute a flare at landing, reducing or eliminating both downward and forward speed at touchdown, in order to avoid injury.[11]

Spacecraft

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Further information: Lander (spacecraft)

Sometimes, a safe landing is accomplished by using multiple forms of lift, thrust (propulsive landing[12]) and dampening systems. Both the Surveyor uncrewed lunar probe craft and the Apollo Lunar Module used a rocket deceleration system and landing gear to soft-land on the Moon. Several Soviet rockets including the Soyuz spacecraft have used parachutes and airbag landing systems to dampen the landing on Earth. In November 2015, Blue Origin's New Shepard became the first rocket to cross the Kármán line (edge of space at 100 km altitude) and land vertically back on Earth. In December 2015, SpaceX's Falcon 9 became the first launch vehicle on an orbital trajectory to successfully vertically-land and recover its first stage, although the landed first stage was on a sub-orbital trajectory.

See also

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Types of landing

Notes

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References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Landing

View on Grokipedia
from Grokipedia
Landing refers to the act or process of arriving at or touching down on a surface, such as land, water, or a platform, following travel through air, sea, or space. This term encompasses various contexts, including aviation, where it denotes the final phase of an aircraft's flight from the approach to touchdown on a runway or other surface, often involving stabilization of speed, descent rate, and configuration for safe contact. In nautical terms, a landing involves a vessel reaching shore or a dock to disembark passengers or cargo. Architecturally, a landing is a flat, level platform located at the top, bottom, or intermediate point of a staircase, providing a transitional space for safety and directional changes in stair flights. Beyond these, the concept extends to space exploration, where spacecraft landings require precise control to achieve soft touchdown on planetary surfaces, and to fisheries, where "landings" quantify the annual catch brought to port in a region. In aviation, landings are categorized by conditions and techniques, including normal, crosswind, short-field, and emergency types, each demanding specific pilot skills to mitigate risks like hard impacts or runway excursions. A hard landing, for instance, occurs when vertical descent exceeds manufacturer limits, potentially causing structural damage, and is defined by touchdown forces surpassing specified g-loads. Stabilized approaches are emphasized in modern standards to ensure consistent outcomes, maintaining a constant glidepath and airspeed from at least 1,000 feet above ground level in instrument conditions. Architectural landings serve functional purposes beyond mere transition, adhering to building codes that mandate minimum dimensions at least as wide as the stair flight, with a minimum depth of 36 inches (910 mm) in residential buildings or the stair width or 48 inches (1,219 mm), whichever is less, in general , for and egress. They often integrate with handrails and may form part of larger designs in multi-story structures. In broader applications, such as space missions, landings represent engineering feats; for example, NASA's Perseverance rover achieved a powered descent and touchdown on Mars in 2021 using terrain-relative navigation for precision. Overall, effective landings across domains prioritize safety, efficiency, and adaptation to environmental factors, influencing design, regulation, and operational protocols worldwide.

General Principles

Physics of Deceleration

Deceleration during landing involves applying external forces to counteract the inertia of a moving vehicle, as described by Newton's first law of motion, which states that an object in motion remains in motion at constant velocity unless acted upon by an unbalanced force. In the context of landing, this inertia manifests as the vehicle's tendency to continue forward or downward motion, requiring deliberate deceleration forces to reduce velocity to zero. Newton's second law further quantifies this process, where the net force FF equals mass mm times acceleration aa (F=maF = ma), with deceleration representing negative acceleration that slows the vehicle while producing forces felt by the structure and occupants. These laws underscore that safe landing demands controlled application of opposing forces to manage the transition from high-speed approach to stationary state without excessive structural stress. The primary forces contributing to energy dissipation in landing are , aerodynamic drag, , and (when reversed). acts downward, influencing the normal force on ground contact and thus amplifying , while drag opposes motion through air resistance, converting into via . Ground , generated between tires or skids and the surface, provides the dominant deceleration on runways or , dissipating as thermal and deformation losses. Reverse from engines or propellers can supplement these by directing backward, further reducing forward . Collectively, these forces work to absorb the vehicle's , given by the KE=12mv2KE = \frac{1}{2} m v^2, where mm is and vv is ; as decreases through work done by drag, , or , this is transformed into non-mechanical forms, enabling a controlled stop. The effectiveness of friction in ground-based deceleration depends on the coefficient of friction μ\mu, which varies significantly by surface type and conditions. On dry runways, μ\mu typically ranges from 0.6 to 0.8 for tires, providing strong braking grip, whereas wet surfaces reduce this to 0.2–0.4 due to hydroplaning risks and reduced contact area. Softer terrains like sand or grass yield even lower coefficients, around 0.1–0.3, limiting deceleration rates and extending stopping distances. Early aviation pioneers, such as the during their 1902 glider tests at Kill Devil Hills, achieved glides exceeding 600 feet on soft sand surfaces, demonstrating the challenges of soft terrains in early flight experiments. In modern applications, these principles apply briefly to wheel brakes for -based slowing or thrusters for thrust-reversal in vacuum landings.

Safety Protocols

Safety protocols for landing prioritize minimizing risks through standardized international guidelines from the (ICAO) and the (FAA), which apply universally across operations. ICAO procedures, outlined in Doc. 8168 (PANS-OPS), mandate decisions if an approach fails to stabilize by 1,000 feet above ground level in or 500 feet in , emphasizing parameters like speed deviations exceeding 10 knots or excessive descent rates. Similarly, FAA standards in the Airplane Flying Handbook require immediate go-arounds for unstabilized approaches below 300 feet above ground level in traffic patterns, with authorized to direct go-arounds if an aircraft's position endangers safety per Doc. 4444 (PANS-ATM). For landings, ICAO and FAA define forced landings as immediate descents necessitated by or other critical issues, requiring pilots to select energy-absorbing , configure flaps for minimum sink speed, and aim for at the lowest controllable while avoiding sink rates over 500 feet per minute. These standards ensure proactive risk mitigation before vehicle-specific execution. Checklist procedures form the core of operational safety, beginning with pre-landing briefs that cover runway conditions, weather minima, and contingency plans such as go-arounds or diversions, typically completed on the downwind leg. timing is critical, initiated at 10-20 feet above the to gradually increase pitch attitude, reducing descent rate while maintaining 1.3 times stall speed, with adjustments for flap settings to prevent hard landings or bounces. Post-touchdown monitoring involves verifying deceleration via brakes, spoilers, and reverse thrust, followed by prompt taxi-off the unless directed otherwise by , to avert excursions. These , integrated into standard operating procedures, promote consistency and error detection during the high-workload landing phase. Risk assessment models quantify threats like runway excursions, which accounted for 97% of runway-related accidents—representing about 30% of all commercial aviation accidents from 1995 to 2008, with an average of nearly 30 incidents per year during that period—highlighting the need for stabilized approaches and contaminated runway evaluations. Such models, often based on historical data from ICAO and FAA databases, inform training and infrastructure improvements to address factors like wet runways or tailwinds. Human factors protocols mitigate physiological and psychological risks, with FAA 120-103A establishing fatigue limits through duty time restrictions—such as no more than 8 hours of per duty period—and biomathematical modeling to avoid operations during the circadian low window (0200-0600 ), which can impair descent performance. (CRM), per FAA AC 120-51D, enhances team coordination during descent by emphasizing clear communication, workload sharing, and briefings to detect errors like unstable approaches, with recurrent via line-oriented flight simulations focusing on landing scenarios. The evolution of landing safety protocols advanced markedly after the 1977 Tenerife disaster, where miscommunication contributed to a runway collision killing 583 people, prompting ICAO to revise Annex 10 and Doc. 4444 for standardized in —such as mandatory use of "takeoff" or "land" clearances without ambiguity—to prevent similar incidents. This shift, along with reinforced CRM principles, has since reduced communication-related errors in approach and landing phases.

Aircraft Landings

Fixed-Wing Procedures

landings involve a structured sequence of phases emphasizing precision, speed control, and alignment with the to ensure safe deceleration on the ground. The process begins with the , where the is configured with landing flaps extended and aligned with the runway centerline, maintaining a stabilized glide path at a constant descent angle, typically 3 degrees, to the intended point. This phase requires a descent rate of 500 to 1,000 feet per minute and airspeed at or above 1.3 times the stall speed in landing configuration (VSO), allowing adjustments for wind gusts while avoiding excessive speed that could lead to floating beyond the target zone. Touchdown zone aiming follows, targeting the first third of the beyond the threshold to maximize rollout distance and safety margins. Pilots maintain visual or instrument reference to this point, using subtle power and pitch inputs to correct deviations without altering the stabilized path; if the is too high or low below 500 feet above ground level, a is mandated to prevent unstabilized contact. The maneuver initiates at 10 to 20 feet above the , involving a gradual increase in through back-elevator pressure to transition from descent to a level attitude, reducing vertical speed for a gentle main gear at or just above speed. This technique demands forward visual focus at a 10- to 15-degree downward angle to judge height accurately, preventing hard impacts or bounces that could damage the undercarriage. Speed management is critical throughout, with the reference landing speed (VREF) serving as the baseline for , calculated as 1.3 times VSO at the 's landing weight to provide a safety margin against . For example, commercial jets often target VREF plus additives for gusts, maintaining it until 50 feet above the threshold before allowing a slight reduction during . Autobrake systems, common on larger , automate wheel braking post-touchdown by applying pressure to achieve a preset deceleration rate (e.g., 3 to 4 meters per second squared), reducing pilot workload and ensuring consistent stopping performance on dry runways. These systems activate upon thrust reverser deployment or weight-on-wheels sensing, though manual override is available for variable conditions. Runway types influence procedure adaptations, with hard-surface runways (e.g., concrete or asphalt) allowing standard techniques due to high friction for braking, while unprepared strips—such as gravel bars or grass fields—demand softer touchdown attitudes to avoid prop strikes or nose-over in taildraggers. In bush flying, common in remote Alaskan or Canadian operations, pilots approach at higher speeds (e.g., 1.5 times VSO) over multiple reconnaissance circuits to assess obstacles, wildlife, or soft spots, then execute a power-on landing to maintain control on uneven terrain. For instance, operations on river gravel require immediate power reduction post-touchdown to prevent hydroplaning, prioritizing directional control over rapid deceleration. Instrumentation like the (ILS) enables low-visibility operations by providing lateral (localizer) and vertical (glideslope) guidance. Category I ILS supports approaches to a decision height of 200 feet with (RVR) of 1,800 feet; Category II to 100 feet and 1,200 feet RVR; and Category III (subdivided into IIIA, IIIB, and IIIC) allows landings with RVR as low as 700 feet or zero, relying on for in or heavy rain. These categories require aircraft equipage with fail-passive or fail-operational systems and crew training for capability. A notable case is the , whose ogival delta-wing design necessitated unique adaptations for subsonic landing, including a high (up to 14 degrees) to generate sufficient low-speed lift via leading-edge vortices. This resulted in a reference landing speed of approximately 160 knots, higher than conventional jets, with drooping ailerons and full-span slats deployed to enhance control and reduce approach noise while managing the aircraft's 185-ton .

Rotary-Wing Techniques

Rotary-wing aircraft, such as helicopters, employ vertical descent techniques that leverage their rotor systems for precise control during landing, distinct from the forward momentum required by fixed-wing aircraft. A fundamental method is the zero-forward-speed touchdown from a hover, where the pilot maintains a stable hover approximately 3 feet above the surface before initiating descent. This involves smoothly lowering the collective pitch to reduce rotor thrust, allowing a controlled vertical descent while using cyclic inputs to counteract any drift and ensure level alignment of the skids or wheels with the landing surface. The collective adjustment must be gradual to prevent abrupt settling, with the pilot monitoring rotor RPM to remain within the green operating range until touchdown, confirming stability before fully unloading the rotors. In emergency scenarios, serves as a critical power-off landing technique, enabling the to descend safely using autorotative airflow through the main blades after failure. The procedure begins with an immediate entry phase, where the is lowered to disengage the and maintain rotor RPM in the optimal range, followed by a steady descent phase at a manufacturer-recommended (typically 50–60 knots for minimum rate of descent). As the nears the ground, the flare phase involves applying aft cyclic to decelerate forward speed and reduce the descent rate, converting into while keeping RPM controlled. The final rundown phase occurs at 3–15 feet above ground level, where forward cyclic levels the attitude, and is raised to cushion the using stored rotor energy, ensuring a level contact to minimize bouncing or rollover risk. Confined area landings demand specialized operations for pinnacles and slopes, where space constraints and terrain irregularities challenge stability. For pinnacle landings on elevated, isolated surfaces, the approach is typically made parallel to the ridgeline into the wind at a steeper angle (up to 15 degrees) to clear obstacles, followed by a hover taxi to position over the forward portion of the area before descent. Ground effect, which increases lift within one rotor diameter of the surface, must be managed carefully during touchdown to avoid sudden loss of cushioning upon clearing the edge, potentially causing settling if airspeed is insufficient. Slope operations involve landing across the incline (recommended maximum 5–8 degrees), using lateral cyclic to keep the upslope skid higher while gradually lowering the downslope skid, ensuring the helicopter remains within tail rotor authority limits to counteract torque. Tail rotor authority is essential for directional control during these maneuvers, but limits arise from factors like low , high power demands, and crosswinds, potentially leading to dynamic rollover. Dynamic rollover occurs when lateral rolling moments—amplified by main exceeding the helicopter's —pivot the aircraft about one skid, reaching a critical bank angle (typically 5–8 degrees) beyond which recovery is impossible. Prevention emphasizes smooth cyclic inputs to neutralize drift, avoiding abrupt changes that could overload the , and immediate reduction of if bank exceeds limits to halt the roll. In counterclockwise systems, right skid-low conditions or left crosswinds heighten risk, necessitating pre-landing reconnaissance of surface conditions. Modern advancements in rotary-wing landing include systems, which enhance precision through automated control laws, particularly in the modified as the ACT/FHS research rotorcraft by the (DLR). These systems employ model-based flight controllers for decoupled axis operation, enabling assisted low-level flight and automated settling on unprepared sites by integrating sensor data for real-time path planning and obstacle avoidance. Flight tests demonstrated improved handling qualities under ADS-33 standards, with the vertical controller facilitating stable hovers and cushioned touchdowns in degraded visual environments, reducing pilot workload during confined or emergency operations.

Influencing Factors

Several external factors influence the success and safety of landings, necessitating procedural adjustments by pilots and air traffic controllers. Among weather elements, s pose a significant challenge by exerting lateral forces that can cause directional control issues during and rollout. For light , the maximum demonstrated crosswind component is typically limited to 15-25 knots, though operational limits may extend to 30 knots depending on the 's pilot operating handbook (POH) and pilot experience; exceeding these can lead to runway excursions. Visibility reductions from , , or impair pilots' ability to acquire visual references for alignment and flare, often requiring instrument approaches with minimum (RVR) thresholds, such as 550 meters for Category I precision approaches under ICAO standards. , particularly low-level shear near the ground, disrupts approach stability by inducing sudden altitude and airspeed variations, prompting pilots to use stabilized approach criteria and potentially if deviations exceed tolerances like ±10 knots in speed. Runway conditions critically affect deceleration and directional control post-touchdown. Dry runways provide higher friction coefficients, typically ranging from 0.50 to 0.80, enabling effective braking with minimal skidding risk. In contrast, wet runways reduce these coefficients to 0.20-0.50 due to water films, increasing stopping distances by up to 15-20% and heightening aquaplaning risks, where tire contact is lost at speeds above approximately 130 km/h (70 knots) in standing water depths exceeding 3 mm. Aircraft mass and configuration also play key roles in landing dynamics. A forward-shifted center of gravity (CG) enhances longitudinal stability during touchdown, reducing pitch oscillations but increasing the elevator forces needed for flare and potentially raising stall speeds. Conversely, an aft CG diminishes stability, making the aircraft more prone to porpoising or bouncing on landing, which is why loading must stay within certified CG envelopes to ensure controlled energy dissipation. Air traffic and further modulate landing operations through spacing and capacity constraints. ICAO standards mandate separation minima, such as 4-6 nautical miles or 2-3 minutes for successive landings behind heavy , to prevent hazardous vortex encounters. Parallel runway operations, enabled by infrastructure like segregated taxiways and minimum 4,300-foot spacing between centerlines, allow simultaneous independent approaches, boosting throughput by up to 50% at major hubs while requiring advanced surveillance for collision avoidance.

Parachute Landings

Deployment and Descent

The parachute's historical development traces back to 1797, when conducted the first successful frameless parachute descent from a hydrogen balloon at approximately 3,200 feet over , using a canopy with a vented umbrella-like design to stabilize the fall. This marked the inception of controlled aerial descent, evolving through military applications in the early to sport parachuting, with significant advancements in the 1970s when round canopies were largely replaced by steerable square (ram-air) designs for improved maneuverability and landing precision. Parachutes used in descent vary by design and purpose, including round canopies, which provide primary drag for non-steerable stabilization; ram-air types, featuring rectangular airfoils that inflate like wings for controlled ; and designs, consisting of fabric strips forming a porous, high-drag structure often employed in high-speed recovery systems. Deployment sequences initiate the process, either via a pilot chute—manually thrown by the jumper to extract the main canopy—or a , a cord attached to the that automatically pulls out the pilot chute upon exit, commonly used in training jumps to ensure timely opening. Upon deployment, canopy inflation occurs rapidly as air fills the fabric, but this phase generates significant deceleration forces, known as opening shock, which can reach several times the jumper's weight; reefing lines temporarily restrict the canopy's diameter during initial inflation to absorb this shock, limiting peak loads to approximately 3-5g for human tolerance in sport applications. This controlled expansion transitions the jumper from freefall deceleration—governed by around 120 mph—to a stabilized descent, with the pilot chute first creating initial drag before the main canopy fully inflates. Steering during descent enhances directional control and landing accuracy, particularly with ram-air parachutes, where toggle controls attached to brake lines allow the jumper to deflect the trailing edge of the canopy—pulling the right toggle induces a left turn, and vice versa—for precise navigation. Round canopies, less responsive, rely on slip maneuvers, such as weight shifting or pulling steering lines to induce sideslip and alter course, though these offer limited precision compared to ram-air systems. In sport skydiving, deployment typically occurs at around 3,000 feet above ground level to allow sufficient time for canopy management and approach planning, following a freefall phase from exit altitudes of 10,000-14,000 feet. Under a fully inflated canopy, descent rates stabilize at 15-20 feet per second, enabling a controlled glide ratio of about 3:1 (forward to vertical drop), which supports safe to the landing area while minimizing ground speed upon touchdown.

Ground Impact Management

Ground impact management in parachuting focuses on techniques and preparations that enable parachutists to safely absorb the forces of touchdown, minimizing injury risk during the final phase of descent. Parachutes typically descend at vertical speeds of 15 to 20 feet per second under normal conditions, requiring precise body positioning and responsive actions to handle these impacts effectively. The recommended landing attitude emphasizes a feet-and-knees position to initiate contact and progressively absorb deceleration forces. Parachutists maintain feet and knees together with knees slightly bent, toes pointed slightly outward, and chin tucked to the chest to protect the ; hands are held low and together near the body to avoid flailing or upon ground contact. This posture allows the initial impact to occur on the balls of the feet, followed by the calves and thighs, distributing vertical and horizontal forces across the lower body before transitioning to a roll if necessary. Central to this management is the (PLF), a roll technique designed to spread impact forces across multiple body points rather than concentrating them on a single area like the legs or . Developed originally by the U.S. military and adopted in skydiving, the PLF begins as the feet touch down, with the parachutist leaning into the direction of travel to initiate a roll involving five points of contact: the balls of the feet, calf, , small of the back, and the opposite . This method converts the downward into a forward roll, reducing peak forces on any one joint or bone and thereby lowering the likelihood of sprains or fractures; parachutists are trained to practice the PLF routinely to ensure proficiency. Obstacle avoidance plays a critical role in preparing for a controlled impact, relying on accurate spotting during descent to select a clear free of hazards such as power lines, trees, or uneven . By 2,000 feet above ground level, parachutists assess the landing area using visual cues to maintain separation from other canopies and avoid restricted zones, employing gentle braked turns under canopy to steer toward open space if needed. In cases of imminent collision with obstacles, reserve deployment serves as a last-resort threshold: decision altitudes are set at no lower than 2,500 feet for students and A-license holders and 1,800 feet for B-, C-, and D-license holders, with a strict cutaway hard deck of 1,000 feet below which the reserve must be deployed without jettisoning the main canopy. Injury data underscores the importance of these techniques, as landings account for the majority of non-fatal incidents in skydiving. According to the United States Parachute Association (USPA), in 2024, 5.6% of surveyed members reported injuries requiring medical treatment, with ankle injuries from improper ground impacts being the most common type. Lower extremity injuries, including sprains and fractures, often result from factors like poor PLF execution or off-heading landings, highlighting the need for vigilant body management. Equipment integration enhances impact protection through proper harness adjustments and helmet standards tailored to absorb landing stresses. Harnesses must be fitted snugly in a piggyback configuration for students, with and chest straps adjusted to distribute suspension forces evenly and prevent shifting during flare or roll, ensuring stable body alignment on . Helmets, required to be rigid for all students except tandems, provide cranial protection against rotational and direct impacts, with ongoing USPA efforts to establish standardized testing for skydiving-specific impact resistance beyond norms.

Spacecraft Landings

Atmospheric Reentry

Atmospheric reentry for landings begins with the vehicle entering a planet's atmosphere at hypersonic velocities, typically 7 to 8 km/s for returns from . This high-speed entry generates intense due to atmospheric compression and , leading to the formation of a plasma sheath around the vehicle as air molecules ionize at temperatures exceeding 10,000 K. The plasma sheath disrupts radio communications, causing a temporary blackout period lasting several minutes, as observed in early missions. Reentry trajectories are carefully planned to follow a precise corridor, balancing skip-out risks from shallow angles and excessive heating from steep descents, with the general physics of drag forces providing the primary deceleration mechanism through atmospheric interaction. Heat management during reentry relies on thermal protection systems, particularly ablative materials that char and erode to carry away heat. For the Apollo capsules, the ablative , composed of epoxy-novalac resin reinforced with silica fibers, withstood peak surface temperatures of approximately 2,760°C (5,000°F) during lunar returns. These materials absorb and dissipate the convective and radiative heat flux, preventing structural failure while the vehicle traverses the most intense heating phase at altitudes between 100 and 50 km. The deceleration profile transitions the from orbital velocities to subsonic speeds primarily through atmospheric drag, with peak g-forces ranging from 4 to 8 g experienced by the . In Apollo missions, maximum decelerations reached about 6.5 to 7 g, occurring around 100 km altitude as builds. Guidance systems, including reaction control thrusters, ensure alignment within the entry corridor by making pre-entry adjustments to the flight path angle and orientation, correcting for dispersions in or position. A seminal event in human atmospheric reentry was Yuri Gagarin's mission on April 12, 1961, marking the first crewed orbital flight and its precursor to controlled landings. During reentry at approximately 7.8 km/s, the spherical capsule encountered plasma sheath formation and peak g-forces of about 8 g, with Gagarin remaining conscious throughout the deceleration. This mission demonstrated the feasibility of human tolerance to reentry environments, influencing subsequent designs for safer trajectories and protection systems.

Surface Interface

The surface interface in spacecraft landings refers to the critical phase of final contact between the vehicle and the , where stabilization and energy dissipation ensure mission success. This process involves specialized hardware and autonomous systems to manage low-velocity impacts on diverse terrains, such as the Moon's or Mars' rocky plains. Unlike high-speed atmospheric reentry, which subjects structures to extreme thermal loads from , the surface interface prioritizes controlled deceleration to velocities typically under 2 m/s to prevent structural damage or tipping. Landing gear designs are engineered to absorb and provide stability upon touchdown. For the Apollo lunar modules, four crushable leg assemblies featured primary and secondary struts filled with aluminum cartridges that deformed to dissipate impact forces, allowing the vehicle to settle on uneven surfaces with slopes up to 12 degrees. In contrast, Mars rovers like Pathfinder, Spirit, and Opportunity employed inflatable airbags surrounding the lander, which bounced across the surface multiple times before deflating, enabling soft deployment in thin atmospheres where parachutes alone are insufficient. These passive systems complement active by handling residual velocities after primary deceleration. Retro-propulsion plays a key role in achieving precise, low-speed , using throttleable engines to perform maneuvers like the hoverslam, where thrust nullifies downward just above the surface. The booster exemplifies this with its engines and grid fins for aerodynamic steering during descent, culminating in a of approximately 1-2 m/s on landing pads or drone ships. Similarly, throttleable descent engines on Mars landers, such as those in the Perseverance rover's sky crane system, enable powered suspension for final positioning. Terrain-relative navigation enhances these capabilities by integrating for 3D mapping and altimeters for real-time detection, allowing autonomous avoidance of boulders or craters during the terminal descent phase, as demonstrated in Perseverance's 2021 landing. Distinctions between soft and hard landings underscore the evolution of surface interface technologies. Soft landings, like Apollo 11's 1969 touchdown at 0.55 m/s vertical velocity in the Sea of Tranquility, relied on pilot-controlled propulsion and crushable gear to achieve stability without significant rebound. The Perseverance rover's 2021 Mars further advanced this to 0.83 m/s using sky crane retro-propulsion and camera-based terrain-relative navigation for hazard avoidance. Hard landings, by comparison, involve higher-impact crashes for uncrewed probes, but modern missions prioritize soft techniques to protect scientific instruments and enable reuse. Looking ahead, NASA's incorporates propulsive landings with human landing systems targeting precision within 50 meters, leveraging integrated and for safe operations near the in the 2020s.

References

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  3. https://theconstructor.org/building/landings-in-staircase/20954/
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  5. https://codes.iccsafe.org/content/IRC2021P3/chapter-3-building-planning#IRC2021P3_Pt03_Ch03_SecR311.7.6
  6. https://codes.iccsafe.org/content/IBC2018P6/chapter-10-means-of-egress#IBC2018P6_Ch10_Sec1011.6
  7. https://www.faa.gov/sites/faa.gov/files/07_phak_ch5_0.pdf
  8. https://www.nasa.gov/wp-content/uploads/2014/10/563410main_ftnl_instructor_manual.pdf
  9. https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/four-forces-on-an-airplane/
  10. https://www.cnatra.navy.mil/training/assets/media/aerodynamics/aero-trainee-guide.pdf
  11. https://openoregon.pressbooks.pub/bodyphysics2ed/chapter/drag-force/
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