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Landing

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.^[1] 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.^[2] In nautical terms, a landing involves a vessel reaching shore or a dock to disembark passengers or cargo.^[1] 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.^[3] 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.^[1] 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.^[2] 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.^[4] 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.^[2] 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 buildings, for accessibility and fire safety egress.^[3]^[5]^[6] They often integrate with handrails and may form part of larger mezzanine 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.^[7] 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 F equals mass m times acceleration a (F = ma), with deceleration representing negative acceleration that slows the vehicle while producing forces felt by the structure and occupants.^[8] 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 gravity, aerodynamic drag, friction, and thrust (when reversed). Gravity acts downward, influencing the normal force on ground contact and thus amplifying friction, while drag opposes motion through air resistance, converting kinetic energy into heat via fluid friction.^[9] Ground friction, generated between tires or skids and the surface, provides the dominant deceleration on runways or terrain, dissipating energy as thermal and deformation losses.^[10] Reverse thrust from engines or propellers can supplement these by directing propulsion backward, further reducing forward momentum. Collectively, these forces work to absorb the vehicle's kinetic energy, given by the formula KE = \frac{1}{2} m v^2, where m is mass and v is velocity; as velocity decreases through work done by drag, friction, or thrust, this energy is transformed into non-mechanical forms, enabling a controlled stop.^[11] The effectiveness of friction in ground-based deceleration depends on the coefficient of friction \mu, which varies significantly by surface type and conditions. On dry concrete runways, \mu typically ranges from 0.6 to 0.8 for aircraft tires, providing strong braking grip, whereas wet surfaces reduce this to 0.2–0.4 due to hydroplaning risks and reduced contact area.^[12] 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 Wright brothers 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.^[13] In modern applications, these principles apply briefly to aircraft wheel brakes for friction-based slowing or spacecraft thrusters for thrust-reversal in vacuum landings.

Safety Protocols

Safety protocols for landing prioritize minimizing risks through standardized international guidelines from the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA), which apply universally across aviation operations. ICAO procedures, outlined in Doc. 8168 (PANS-OPS), mandate go-around decisions if an approach fails to stabilize by 1,000 feet above ground level in instrument meteorological conditions or 500 feet in visual meteorological conditions, emphasizing parameters like speed deviations exceeding 10 knots or excessive descent rates.^[14] 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 air traffic control authorized to direct go-arounds if an aircraft's position endangers safety per Doc. 4444 (PANS-ATM).^[2] For emergency landings, ICAO and FAA define forced landings as immediate descents necessitated by engine failure or other critical issues, requiring pilots to select energy-absorbing terrain, configure flaps for minimum sink speed, and aim for touchdown at the lowest controllable airspeed while avoiding sink rates over 500 feet per minute.^[15] 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.^[2] Flare timing is critical, initiated at 10-20 feet above the runway 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 runway unless directed otherwise by air traffic control, to avert excursions.^[2] These checklists, 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.^[16] 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 Advisory Circular 120-103A establishing fatigue limits through duty time restrictions—such as no more than 8 hours of flight time per duty period—and biomathematical modeling to avoid operations during the circadian low window (0200-0600 local time), which can impair descent performance.^[17] Crew resource management (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 training via line-oriented flight simulations focusing on landing scenarios.^[18] 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 phraseology in air traffic control—such as mandatory use of "takeoff" or "land" clearances without ambiguity—to prevent similar incidents.^[19] This shift, along with reinforced CRM principles, has since reduced communication-related errors in approach and landing phases.

Aircraft Landings

Fixed-Wing Procedures

Fixed-wing aircraft landings involve a structured sequence of phases emphasizing precision, speed control, and alignment with the runway to ensure safe deceleration on the ground. The process begins with the final approach, where the aircraft 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 touchdown 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 (V_SO), allowing adjustments for wind gusts while avoiding excessive speed that could lead to floating beyond the target zone.^[2] Touchdown zone aiming follows, targeting the first third of the runway 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 aircraft is too high or low below 500 feet above ground level, a go-around is mandated to prevent unstabilized contact. The flare maneuver initiates at 10 to 20 feet above the runway, involving a gradual increase in angle of attack through back-elevator pressure to transition from descent to a level attitude, reducing vertical speed for a gentle main gear touchdown at or just above stall 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.^[2] Speed management is critical throughout, with the reference landing speed (V_REF) serving as the baseline for final approach, calculated as 1.3 times V_SO at the aircraft's landing weight to provide a safety margin against stall. For example, commercial jets often target V_REF plus additives for gusts, maintaining it until 50 feet above the threshold before allowing a slight reduction during flare. Autobrake systems, common on larger aircraft, 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.^[20]^[21] 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 V_SO) 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.^[22] Instrumentation like the Instrument Landing System (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 runway visual range (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 autopilot for touchdown in fog or heavy rain. These categories require aircraft equipage with fail-passive or fail-operational systems and crew training for autoland capability.^[23] A notable case is the Concorde supersonic transport, whose ogival delta-wing design necessitated unique adaptations for subsonic landing, including a high angle of attack (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 maximum landing weight.^[24]^[25]

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.^[26] 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.^[26] In emergency scenarios, autorotation serves as a critical power-off landing technique, enabling the helicopter to descend safely using autorotative airflow through the main rotor blades after engine failure. The procedure begins with an immediate entry phase, where the collective is lowered to disengage the engine clutch and maintain rotor RPM in the optimal range, followed by a steady descent phase at a manufacturer-recommended airspeed (typically 50–60 knots for minimum rate of descent).^[27] As the helicopter nears the ground, the flare phase involves applying aft cyclic to decelerate forward speed and reduce the descent rate, converting kinetic energy into rotor momentum while keeping RPM controlled.^[27] The final rundown phase occurs at 3–15 feet above ground level, where forward cyclic levels the attitude, and collective is raised to cushion the touchdown using stored rotor energy, ensuring a level contact to minimize bouncing or rollover risk.^[27] 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.^[26] 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.^[26] 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.^[26] Tail rotor authority is essential for directional control during these maneuvers, but limits arise from factors like low airspeed, high power demands, and crosswinds, potentially leading to dynamic rollover. Dynamic rollover occurs when lateral rolling moments—amplified by main rotor thrust exceeding the helicopter's weight—pivot the aircraft about one skid, reaching a critical bank angle (typically 5–8 degrees) beyond which recovery is impossible.^[27] Prevention emphasizes smooth cyclic inputs to neutralize drift, avoiding abrupt collective changes that could overload the tail rotor, and immediate reduction of collective if bank exceeds limits to halt the roll.^[27] In counterclockwise rotor systems, right skid-low conditions or left crosswinds heighten risk, necessitating pre-landing reconnaissance of surface conditions.^[28] Modern advancements in rotary-wing landing include fly-by-wire systems, which enhance precision through automated control laws, particularly in the Eurocopter EC135 modified as the ACT/FHS research rotorcraft by the German Aerospace Center (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.^[29] 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.^[29]

Influencing Factors

Several external factors influence the success and safety of aircraft landings, necessitating procedural adjustments by pilots and air traffic controllers. Among weather elements, crosswinds pose a significant challenge by exerting lateral forces that can cause directional control issues during touchdown and rollout. For light general aviation aircraft, the maximum demonstrated crosswind component is typically limited to 15-25 knots, though operational limits may extend to 30 knots depending on the aircraft's pilot operating handbook (POH) and pilot experience; exceeding these can lead to runway excursions.^[2] Visibility reductions from fog, precipitation, or haze impair pilots' ability to acquire visual references for alignment and flare, often requiring instrument approaches with minimum runway visual range (RVR) thresholds, such as 550 meters for Category I precision approaches under ICAO standards.^[30] Turbulence, 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 go-around if deviations exceed tolerances like ±10 knots in speed.^[31] 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.^[32] 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.^[33]^[34] 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.^[7] 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.^[35] Air traffic and airport infrastructure further modulate landing operations through spacing and capacity constraints. ICAO standards mandate wake turbulence separation minima, such as 4-6 nautical miles or 2-3 minutes for successive landings behind heavy aircraft, to prevent hazardous vortex encounters.^[36] Parallel runway operations, enabled by infrastructure like segregated taxiways and minimum 4,300-foot spacing between centerlines, allow simultaneous independent approaches, boosting airport throughput by up to 50% at major hubs while requiring advanced surveillance for collision avoidance.^[37]

Parachute Landings

Deployment and Descent

The parachute's historical development traces back to 1797, when André-Jacques Garnerin conducted the first successful frameless parachute descent from a hydrogen balloon at approximately 3,200 feet over Paris, using a silk canopy with a vented umbrella-like design to stabilize the fall.^[38] This marked the inception of controlled aerial descent, evolving through military applications in the early 20th century 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.^[39] 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 gliding; and ribbon designs, consisting of fabric strips forming a porous, high-drag structure often employed in high-speed recovery systems.^[40]^[41] Deployment sequences initiate the process, either via a pilot chute—manually thrown by the jumper to extract the main canopy—or a static line, a cord attached to the aircraft that automatically pulls out the pilot chute upon exit, commonly used in training jumps to ensure timely opening.^[42] 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.^[43] This controlled expansion transitions the jumper from freefall deceleration—governed by terminal velocity around 120 mph—to a stabilized descent, with the pilot chute first creating initial drag before the main canopy fully inflates.^[44] 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.^[45] 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.^[46] 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.^[47] Under a fully inflated canopy, descent rates stabilize at 15-20 feet per second, enabling a controlled glide ratio of about 3:1 (forward distance to vertical drop), which supports safe navigation to the landing area while minimizing ground speed upon touchdown.^[48]

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.^[47]^[48] 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 neck; hands are held low and together near the body to avoid flailing or injury 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.^[49] Central to this management is the Parachute Landing Fall (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 torso. 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, thigh, small of the back, and the opposite shoulder. This method converts the downward momentum 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.^[49]^[50] Obstacle avoidance plays a critical role in preparing for a controlled impact, relying on accurate spotting during descent to select a clear landing zone free of hazards such as power lines, trees, or uneven terrain. 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 parachute 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.^[51]^[52] 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.^[53] 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 leg and chest straps adjusted to distribute suspension forces evenly and prevent shifting during flare or roll, ensuring stable body alignment on touchdown. 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 general aviation norms.^[54]^[55]^[56]

Spacecraft Landings

Atmospheric Reentry

Atmospheric reentry for spacecraft landings begins with the vehicle entering a planet's atmosphere at hypersonic velocities, typically 7 to 8 km/s for returns from low Earth orbit.^[57] This high-speed entry generates intense aerodynamic heating due to atmospheric compression and friction, leading to the formation of a plasma sheath around the vehicle as air molecules ionize at temperatures exceeding 10,000 K.^[58] 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.^[59] 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 Avcoat 5026-39 ablative heat shield, composed of epoxy-novalac resin reinforced with silica fibers, withstood peak surface temperatures of approximately 2,760°C (5,000°F) during lunar returns.^[60]^[61] 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 spacecraft from orbital velocities to subsonic speeds primarily through atmospheric drag, with peak g-forces ranging from 4 to 8 g experienced by the crew.^[62] In Apollo missions, maximum decelerations reached about 6.5 to 7 g, occurring around 100 km altitude as dynamic pressure builds.^[63] 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 velocity or position.^[59] A seminal event in human atmospheric reentry was Yuri Gagarin's Vostok 1 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.^[64] 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 planetary surface, 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 regolith or Mars' rocky plains. Unlike high-speed atmospheric reentry, which subjects structures to extreme thermal loads from friction, the surface interface prioritizes controlled deceleration to velocities typically under 2 m/s to prevent structural damage or tipping.^[66] Landing gear designs are engineered to absorb kinetic energy and provide stability upon touchdown. For the Apollo lunar modules, four crushable leg assemblies featured primary and secondary struts filled with aluminum honeycomb cartridges that deformed to dissipate impact forces, allowing the vehicle to settle on uneven surfaces with slopes up to 12 degrees.^[67] 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.^[68] These passive systems complement active propulsion by handling residual velocities after primary deceleration. Retro-propulsion plays a key role in achieving precise, low-speed touchdowns, using throttleable engines to perform maneuvers like the hoverslam, where thrust nullifies downward velocity just above the surface. The SpaceX Falcon 9 booster exemplifies this with its Merlin engines and grid fins for aerodynamic steering during descent, culminating in a touchdown velocity of approximately 1-2 m/s on landing pads or drone ships.^[69] 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 LIDAR for 3D mapping and radar altimeters for real-time hazard detection, allowing autonomous avoidance of boulders or craters during the terminal descent phase, as demonstrated in Perseverance's 2021 landing.^[70]^[66] 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.^[71] The Perseverance rover's 2021 Mars landing 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 Artemis program incorporates propulsive landings with human landing systems targeting precision within 50 meters, leveraging integrated LIDAR and Doppler radar for safe operations near the lunar south pole in the 2020s.^[72]

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Dynamic Rollover
Tail rotor thrust and wind drag on the fuselage contribute to roll moment. In helicopters that are equipped with main rotor systems that turn clockwise (when ...Missing: prevention | Show results with:prevention<|separator|>
[28]
Results of the Pilot Assistance System “Assisted Low-Level Flight ...
Aug 7, 2025 · [1] [2] [3]. The ACT/FHS is based on a Eurocopter EC135, a light, twin-engine helicopter with a bearingless main rotor and a fenestron. ...Missing: settling | Show results with:settling
[29]
Low-Visibility Procedures (LVP) | SKYbrary Aviation Safety
As visibility deteriorates, the potential for runway incursions by aircraft, vehicles or personnel increases. The risk of inadvertent runway incursion by ...
[30]
[PDF] Evaluating the Effect of Turbulence on Aircraft During Landing and ...
Vertical wind shear causes variations of the horizontal component of the wind which can affect the aircraft speed on approach to landing or on take-off.
[31]
Runway Surface Friction | SKYbrary Aviation Safety
Runway surface friction affects braking after landing. Less friction means less braking. It's measured by the coefficient of friction, and is related to ...
[32]
Surface Metrology Techniques to Improve Runway Materials - AZoM
Mar 17, 2021 · The conclusion was that the wet runway's friction coefficients, compared to the dry runway, decreased by 0.36 and 0.38 in partial hydroplaning ...
[33]
The Science of Aircraft Hydroplaning - Pilot Institute
Jun 16, 2023 · It's one of the most common risk factors for runway excursions and can cause anything from a mild scare for a pilot to a deadly crash.
[34]
How Does CG Affect Aircraft Performance? - Boldmethod
The relationship between aircraft performance and CG location is simple: by moving the CG forward and aft, you change the amount of tail down force and lift ...
[35]
There's An Airplane On The Runway. Can I Land? - Boldmethod
Sep 23, 2025 · 1) 3,000 Feet of Separation: Category I aircraft landing behind Category I or II. 2) 4,500 Feet of Separation: Category II aircraft landing ...
[36]
Parallel Runway Operation | SKYbrary Aviation Safety
The main objective of implementing simultaneous operations on parallel or near-parallel runways is to increase runway capacity and aerodrome flexibility.
[37]
Navigating the Impact of Climate Change on Aviation
Feb 3, 2025 · Wind shear has increased by 15% at cruising altitudes since satellites started observing it in 1979. Experts predict additional increases of 17% ...
[38]
1797 - The modern world's first parachute jump - FAI.org
Oct 22, 2017 · Two-hundred and twenty years ago today, on 22 October 1797, pioneering balloonist André-Jacques Garnerin became the modern world's first successful parachutist.
[39]
A Brief History of the Parachute - Popular Mechanics
Feb 29, 2012 · The military is currently undergoing a complete conversion from circular to square canopies. The new T-11 chutes have been shown to decrease ...``the Flying Man'' · Garnerin's Parachute · The Packed Chute, The...
[40]
Parachute | Aeronautical Safety Device | Britannica
The sport parachute has evolved over the years from the traditional round parachute to the square (actually rectangular) ram-air airfoils commonly seen today.
[41]
[PDF] DEVELOPMENT AND TESTING OF A DROGUE PARACHUTE ...
All but one parachute design had a conical ribbon gore pattern, with the one remaining design using a conical ring-slot canopy pattern. All of the parachute ...
[42]
A skydiver's equipment is made up of three main parachute system ...
Deployment - The pilot chute is attached to the rest of the parachute by a length of fabric webbing or tape, called a bridle. Midway along the bridle is a pin ...
[43]
[PDF] Parachute Recovery Systems Design Manual - DTIC
Dec 20, 2024 · ... Landing Analysis .............................................. ... 6-101. 6.8.2 Relationship of Deceleration ... Energy Absorption Diagram ...
[44]
[PDF] 19670022936.pdf - NASA Technical Reports Server
The parachute was deployed unreefed and the test objectives were to observe the dynamics of parachute deployment and inflation and to measure opening shock ...
[45]
Building Better Canopy Control with Four Basic Tools
May 17, 2024 · Steer the parachute; Change airspeed/glide/rate of descent; Flare for a soft and safe landing. Jumpers are experienced and comfortable with ...Missing: ram- slip round
[46]
The Proper Way To Steer A Parachute - Skydive Paraclete XP
May 26, 2020 · Round parachutes could only be “steered” by pivoting around the center point of the canopy. If you were the canopy pilot in control of a round ...Missing: slip | Show results with:slip
[47]
Chapter 5 - United States Parachute Association
Jumpers should open no lower than 3,000 feet AGL to provide ample time to prepare for water entry, especially when the landing area is a small body of water and ...
[48]
How Fast Do You Fall When Skydiving
Tandem canopies are designed to be docile and will have a vertical descent rate of about 15mph – give or take a little for the weight of the two jumpers. So if ...Missing: 15-20 s
[49]
Category A (Arch) - United States Parachute Association
Parachute Landing Fall (PLF). Performing a PLF can help you reduce the risk of injury during landing by distributing the impact across five points of your body.
[50]
Glossary - United States Parachute Association
PARACHUTE LANDING FALL (PLF) A method developed by the U.S. military to minimize the chance of injury from a hard landing under parachute. The jumper ...
[51]
United States Parachute Association > Experienced Skydivers > SIM > Chapter 4
### USPA Recommendations Summary (Chapter 4)
[52]
How Safe is Skydiving? - United States Parachute Association
Injuries. 5.6% of members reported that they experienced an injury that required medical treatment in 2024, the most common being ankle injuries from landings.
[53]
2-1: Basic Safety Requirements - United States Parachute Association
All students must jump with one USPA AFF rating holder, exit safely, maintain stability, and deploy at the planned altitude without assistance prior to ...
[54]
Safety Check | Harness-and-Container Fit
Aug 1, 2018 · A properly sized and adjusted harness-and-container is essential to your safety both in freefall and under canopy.Missing: helmet impact protection
[55]
Creating a Better Brain Bucket—Skydiving Helmets Step Toward ...
Jul 1, 2019 · The standard for impact is different across a bunch of different sports. Generally, the helmet must be stress tested under different ...Missing: harness | Show results with:harness
[56]
Re-Entry Aircraft
The aircraft is said to be hypersonic. Typical low earth orbit re-entry speeds are near 17,500 mph and the Mach number M is nearly twenty five, M < 25.Missing: km/ | Show results with:km/
[57]
[PDF] REENTRY PLASMA EFFECTS
Radio transmission between the ground and a space vehicle is, in general, degraded or inter- rupted by the plasma sheath that forms about the vehicle as it ...
[58]
[PDF] Spacecraft Design Considerations for Piloted Reentry and Landing
Jan 14, 2004 · The maximum deceleration during direct entry is dependent upon the vehicle's path angle, initial velocity, and atmospheric characteristics.
[59]
[PDF] THERMAL PROTECTION SUBSYSTEM
The Apollo thermal protection subsystem protected the command module during lunar-return entry, designed for the first manned spacecraft to enter earth's ...Missing: peak | Show results with:peak
[60]
5,000°F - NASA
Oct 12, 2018 · It's a material that will shed heat as you reenter the atmosphere. The temperature goes up, you get up to the surface temperature of about 5000 ...Missing: peak | Show results with:peak
[61]
Apollo 11 Flight Journal - Day 9, part 2: Entry and Splashdown - NASA
Mar 7, 2021 · At 194 hours, 16 minutes; Apollo 11 is 7,512 nautical miles [13,912 km] from Earth, velocity 20,304 feet per second [6,189 m/s]. 194:16:36 ...
[62]
Re-entry and Splashdown - Apollo 8 - NASA
May 4, 2024 · But as it hits the first breaking point at 180,000 feet, the max g force will be felt by the crew, of 6.8 g's. A second g spike of 4.2 will be ...
[63]
ESA - The flight of Vostok 1 - European Space Agency
As Gagarin continues his descent, he experiences about 8g during reentry but remains conscious. Vostok 1 is still 7 km from the ground when the hatch of the ...
[64]
April 1961 - First Human Entered Space - NASA
Nov 3, 2023 · His vehicle, Vostok 1 circled Earth at a speed of 27,400 kilometers per hour with the flight lasting 108 minutes. Vostok's reentry was ...
[65]
Impact Story: Terrain Relative Navigation - NASA
Sep 30, 2022 · Terrain Relative Navigation (TRN), a technology developed by NASA, facilitates increased landing accuracy and helps spacecraft avoid surface hazards.Missing: radar | Show results with:radar
[66]
[PDF] apollo lunar module landing gear
In evaluating the lunar module touchdown performance, strut stroking and toppling stability are the prime factors and are governed primarily by touchdown ...
[67]
Mars Pathfinder - NASA Science
Nov 6, 2024 · The computer inflated these large air bags about 330 feet (100 meters) above the surface of Mars. Upon landing, the airbag-encased Pathfinder ...
[68]
Falcon 9 - SpaceX
Falcon 9 is a reusable, two-stage rocket designed and manufactured by SpaceX for the reliable and safe transport of people and payloads into Earth orbit and ...
[69]
[PDF] Mars Entry, Descent, and Landing Instrumentation 2 Trajectory ...
The reconstructed velocity magnitude at touchdown is 0.828 m/s. The vehicle body Euler angles relative to the North-East-Down frame along with the total ...<|control11|><|separator|>
[70]
[PDF] An Analysis and Historical Review of the Apollo Program Lunar ...
The final touchdown velocity envelope—i.e., the Doghouse—is shown in Figure 5 with the noted boundaries for landing gear energy absorption and landing stability ...
[71]
NASA Advances Precision Landing Technology with Field Test at ...
Apr 29, 2025 · NASA's official lunar landing requirement is to be able to land within 50 meters (164 feet) of the targeted site and developing precision tools ...