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Hangar	A hangar is a large, enclosed structure used for housing, servicing, and maintaining aircraft. Hangars protect aircraft from environmental factors such as wind, rain, and sunlight. They are commonly found at airports, military bases, and private aviation facilities, and they vary in size depending on the type of aircraft they accommodate.
Hard Landing	A hard landing occurs when an aircraft touches down with excessive vertical speed or force. This can result from pilot error, adverse weather conditions, or mechanical issues. Hard landings can cause structural damage to the aircraft, including stress fractures in the landing gear, requiring maintenance checks before the next flight.
Heading	Heading refers to the direction an aircraft's nose is pointing, measured in degrees relative to true north or magnetic north. It is different from the aircraft’s track, which is the actual path over the ground. Pilots use heading indicators and magnetic compasses to maintain and adjust their heading for navigation.
Heading Indicator	A heading indicator is a flight instrument that displays an aircraft’s current heading in degrees. Unlike magnetic compasses, heading indicators are not affected by acceleration or turning errors, making them more reliable for navigation.
Headwind	A headwind is a wind that blows directly opposite to an aircraft’s direction of travel. While headwinds increase fuel consumption and reduce ground speed, they are beneficial during takeoff and landing because they generate additional lift, allowing for shorter runway distances and improved climb performance.
Heat Exchanger	A heat exchanger is a component in an aircraft’s environmental control system that regulates temperature by transferring heat between fluids or air. It helps maintain cabin comfort, engine cooling, and fuel efficiency.
Height Above Ground Level (AGL)	The height of an aircraft measured relative to the ground directly below it, rather than sea level. This measurement is critical for landing approaches, obstacle clearance, and terrain awareness. Pilots use AGL values from radar altimeters or instrument charts to ensure safe altitude levels during low-level flight.
Helicopter	A helicopter is a type of rotary-wing aircraft that uses one or more horizontal rotors to generate lift and thrust. Unlike fixed-wing aircraft, helicopters can hover, take off, and land vertically, making them ideal for search-and-rescue missions, medical evacuations, law enforcement, and military applications.
Helicopter Rotor System	The rotor system of a helicopter consists of blades, a mast, and a hub, providing lift and directional control. Rotor systems can be single, dual, or coaxial, each offering specific advantages in maneuverability and performance.
Helipad	A helipad is a designated landing and takeoff area for helicopters. Helipads can be located on rooftops, ships, hospitals, or dedicated airfields. They are marked with an "H" symbol and may include lighting systems for night operations. Some helipads also have fueling and maintenance facilities.
Heliport	A heliport is a small airport designed specifically for helicopter operations. Unlike helipads, which are singular landing spots, heliports may include multiple landing areas, maintenance facilities, refueling stations, and air traffic control services for managing helicopter traffic.
High-Altitude Operations	High-altitude operations involve flights at altitudes above 25,000 feet, where reduced oxygen levels and air pressure affect both aircraft performance and human physiology. Pilots require supplemental oxygen systems, and aircraft must be pressurized or equipped with oxygen masks to sustain operations safely at high altitudes.
High-Bypass Turbofan Engine	A high-bypass turbofan engine is a type of jet engine that uses a large fan to generate most of its thrust by bypassing air around the engine core. This design increases fuel efficiency, reduces noise, and improves overall performance, making it the preferred engine type for commercial airliners.
High-Density Altitude	High-density altitude refers to conditions where air pressure and temperature reduce aircraft performance, effectively simulating a higher elevation. It decreases engine power, lift, and climb performance, requiring pilots to adjust takeoff distances and power settings accordingly.
High-Drag Configuration	A high-drag configuration refers to aircraft settings that increase aerodynamic resistance, such as deploying landing gear, extending flaps, or using speed brakes. This configuration helps pilots slow down efficiently when descending or preparing for landing.
High-Lift Devices	High-lift devices are aerodynamic surfaces, such as flaps and slats, designed to increase lift at low speeds. These devices improve an aircraft’s takeoff and landing performance by allowing it to generate more lift at lower airspeeds, reducing runway length requirements.
High-Lift Wing	A high-lift wing is an aircraft wing designed with features such as slats, flaps, and curved profiles to maximize lift generation. These wings are commonly found on transport aircraft and military cargo planes to enable operations from short or unpaved runways.
High-Speed Taxiway	A high-speed taxiway is a specially designed taxiway that allows aircraft to exit the runway at high speeds after landing. These taxiways are angled to facilitate smooth and rapid deceleration, improving airport efficiency by reducing runway occupancy times.
Holding Fuel	Holding fuel is extra fuel carried by an aircraft to account for delays, diversions, or holding patterns. Air traffic congestion, weather conditions, or emergency situations may require additional fuel reserves to ensure the aircraft can reach an alternate airport safely.
Holding Pattern	A holding pattern is a racetrack-shaped maneuver used by aircraft when awaiting landing clearance. Aircraft enter a holding pattern when instructed by air traffic control due to congestion, weather delays, or emergency situations. Pilots follow specific altitude and timing guidelines to maintain safe separation from other aircraft.
Horizontal Stabilizer	A horizontal stabilizer is a fixed aerodynamic surface located at the tail of an aircraft. It provides stability by preventing excessive pitching movements. The stabilizer often includes an elevator, which pilots use to control the aircraft’s pitch, adjusting its nose-up or nose-down attitude.
Hot Start	A hot start occurs when an aircraft engine, particularly a turbine engine, experiences excessive internal temperatures during startup. This can result from improper fuel-air mixture settings or engine malfunction. Hot starts can damage engine components and require immediate shutdown and inspection.
Hovering	Hovering is a flight condition in which a helicopter maintains a fixed position above the ground using rotor thrust. Unlike airplanes, helicopters do not need forward motion to generate lift. Precise control of pitch, yaw, and collective inputs is required to maintain a stable hover.
Hub-and-Spoke System	A hub-and-spoke system is a network model used by airlines to connect smaller regional airports to central hub airports. Passengers travel to major hubs before connecting to their final destinations. This system improves efficiency by consolidating flights and maximizing aircraft utilization.
Hybrid-Electric Aircraft	A hybrid-electric aircraft uses a combination of traditional fuel-powered engines and electric propulsion systems. This technology aims to reduce fuel consumption, emissions, and noise while maintaining performance. Hybrid aircraft are in development for commercial and military applications.
Hydraulic Failure	Hydraulic failure occurs when an aircraft’s hydraulic system loses pressure or experiences a mechanical fault. This can affect landing gear, flight controls, and braking systems. Pilots follow emergency checklists to switch to backup systems or perform alternative landing procedures.
Hydraulic System	The hydraulic system in an aircraft uses pressurized fluid to operate critical components such as landing gear, brakes, flaps, and flight controls. Hydraulic systems provide reliable and powerful force transmission, essential for large and high-performance aircraft.
Hydroplaning	Hydroplaning occurs when an aircraft’s tires lose contact with the runway surface due to a layer of water. This reduces braking effectiveness and directional control, increasing the risk of runway overruns. Pilots minimize hydroplaning risks by using proper landing techniques and braking strategies.
Hypersonic Flight	Hypersonic flight refers to aircraft traveling at speeds greater than Mach 5 (five times the speed of sound). Hypersonic technology is being researched for military, space, and commercial applications, enabling ultra-fast travel and high-altitude reconnaissance missions.
Hypoxia	Hypoxia is a medical condition caused by insufficient oxygen reaching the body’s tissues, often occurring at high altitudes. Symptoms include dizziness, confusion, and impaired decision-making. Pilots operating above 12,500 feet must use supplemental oxygen to prevent hypoxia and ensure safe flight operations.