AirbandAirband or Aircraft band is the name for a group of frequencies in the VHF radio spectrumallocated to radio communication in civil aviation, sometimes also referred to as VHF, orphonetically as "Victor". Different sections of the band are used for radionavigational aids andair traffic control.In most countries a license to operate airband equipment is required and the operator is tested oncompetency in procedures, language and the use of the phonetic alphabet.Spectrum usageAntenna array at Amsterdam Airport SchipholThe VHF airband uses the frequencies between 108 and 137 MHz. The lowest 10 MHz of theband, from 108–117.95 MHz, is split into 200 narrow-band channels of 50 kHz.Channel spacingChannel spacing for voice communication on the airband was originally 200 kHzuntil 1947,providing 70 channels from 118 to 132 MHz. Some radios of that time provided receive-onlycoverage below 118 MHz for a total of 90 channels. From 1947–1958 the spacing became100 kHz; from 1954 split once again to 50 kHz and the upper limit extended to 135.95 MHz (360channels), and then to 25 kHz in 1972 to provide 720 usable channels. On 1 January 1990 thefrequencies between 136.000 and 136.975 MHz were added, resulting in 760 channels.
Increasing air traffic congestion has led to further subdivision into narrow-band 8.33 kHzchannels in the ICAO European region; all aircraft flying above 19,500 feet are required to havecommunication equipment for this channel spacing.Outside of Europe, 8.33 kHzchannels are permitted in many countries but not widely used as of 2012.The emergency communication channel 121.5 MHz is the only channel that retains 100 kHzbandwidth.GPS offers an inexpensive and reliable supplement to existing navigation techniques for aircraft.Civil aircraft typically fly from one ground beacon, or waypoint, to another. With GPS, anaircrafts computers can be programmed to fly a direct route to a destination. The savings in fueland time can be significant.GPS can simplify and improve the method of guiding planes to a safe landing, especially in poorweather. With advanced GPS systems, airplanes can be guided to touchdown even when visibilityis poor. For the private pilot, inexpensive GPS systems provide position information in apractical, simple, and useful form.GPS Navigation in the AirPilots on long distance flights withoutGPS rely on navigational beacons locatedacross the country. Using GPS, aircraftcan fly the most direct routes betweenairports.
GPS in the CockpitPilots often rely on GPS to navigate totheir destinations. A GPS receiver in thecockpit provides the pilot with accurateposition data and helps him or her keepthe airplane on course.Flight instrumentsFlight instruments are the instruments in the cockpit of an aircraft that provide the pilot withinformation about the flight situation of that aircraft, such as altitude, speed and direction. The flightinstruments are of particular use in conditions of poor visibility, such as in clouds, when suchinformation is not available from visual reference outside the aircraft.Flight instrumentsMost regulated aircraft have these flight instruments:AltimeterThe altimeter shows the aircrafts altitude above sea-level by measuring the difference betweenthe pressure in a stack of aneroid capsules inside the altimeter and the atmospheric pressureobtained through the static system. It is adjustable for local barometric pressure which must beset correctly to obtain accurate altitude readings. As the aircraft ascends, the capsules expand andthe static pressure drops, causing the altimeter to indicate a higher altitude. The opposite effectoccurs when descending.Attitude indicatorThe attitude indicator (also known as an artificial horizon) shows the aircrafts attitude relative tothe horizon. From this the pilot can tell whether the wings are level and if the aircraft nose ispointing above or below the horizon. This is a primary instrument for instrument flight and is
also useful in conditions of poor visibility. Pilots are trained to use other instruments incombination should this instrument or its power fail.Schempp-Hirth Janus-C glider Instrument panel equipped for "cloud flying". The turn and bank indicatoris top center. The heading indicator is replaced by a GPS-driven computer with wind and glide data,driving two electronic variometer displays to the right.Airspeed indicatorThe airspeed indicator shows the aircrafts speed (usually in knots ) relative to the surroundingair. It works by measuring the ram-air pressure in the aircrafts pitot tube. The indicated airspeedmust be corrected for air density (which varies with altitude, temperature and humidity) in orderto obtain the true airspeed, and for wind conditions in order to obtain the speed over the ground.Magnetic compassThe compass shows the aircrafts heading relative to magnetic north. While reliable in steadylevel flight it can give confusing indications when turning, climbing, descending, or accelerating
due to the inclination of the Earths magnetic field. For this reason, the heading indicator is alsoused for aircraft operation. For purposes of navigation it may be necessary to correct thedirection indicated (which points to a magnetic pole) in order to obtain direction of true north orsouth (which points to the Earths axis of rotation).Heading indicatorThe heading indicator (also known as the directional gyro, or DG; sometimes also called thegyrocompass, though usually not in aviation applications) displays the aircrafts heading withrespect to magnetic north. Principle of operation is a spinning gyroscope, and is therefore subjectto drift errors (called precession) which must be periodically corrected by calibrating theinstrument to the magnetic compass. In many advanced aircraft (including almost all jet aircraft),the heading indicator is replaced by a Horizontal Situation Indicator (HSI) which provides thesame heading information, but also assists with navigation.Vertical speed indicatorThe VSI (also sometimes called a variometer, or rate of climb indicator) senses changing airpressure, and displays that information to the pilot as a rate of climb or descent in feet perminute, meters per second or knots.Additional panel instruments that may not be found in smaller aircraftCourse deviation indicatorThe CDI is an avionics instrument used in aircraft navigation to determine an aircrafts lateralposition in relation to a track, which can be provided by a VOR or an Instrument LandingSystem.This instrument can also be integrated with the heading indicator in a horizontal situationindicator.Radio Magnetic Indicator
An RMI is generally coupled to an automatic direction finder (ADF), which provides bearing fora tuned Non-directional beacon (NDB). While simple ADF displays may have only one needle, atypical RMI has two, coupled to different ADF receivers, allowing for position fixing using oneinstrument.Basic Sixaltimeter (feet)airspeed indicator (knots)turn and bank indicator (turn direction and coordination)vertical speed indicator (feet per minute)artificial horizon (attitude indication)directional gyro / heading indicator (degrees)Aircraft flight control systemA conventional fixed-wing aircraft flight control system consists of flight control surfaces, the respectivecockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraftsdirection in flight. Aircraft engine controls are also considered as flight controls as they change speed.Cockpit controlsPrimary controlsGenerally, the primary cockpit flight controls are arranged as follows:a control yoke (also known as a control column), centre stick or side-stick (the latter two alsocolloquially known as a control or joystick), governs the aircrafts roll and pitch by moving theailerons (or activating wing warping on some very early aircraft designs) when turned ordeflected left and right, and moves the elevators when moved backwards or forwardsrudder pedals, or the earlier, pre-1919 "rudder bar", to control yaw, which move the rudder; leftfoot forward will move the rudder left for instance.throttle controls to control engine speed or thrust for powered aircraft.Secondary controlsIn addition to the primary flight controls for roll, pitch, and yaw, there are often secondarycontrols available to give the pilot finer control over flight or to ease the workload. The mostcommonly available control is a wheel or other device to control elevator trim, so that the pilotdoes not have to maintain constant backward or forward pressure to hold a specific pitch attitude.
Flight control systemsMechanicalde Havilland Tiger Moth elevator and rudder cablesMechanical or manually operated flight control systems are the most basic method of controllingan aircraft. They were used in early aircraft and are currently used in small aircraft where theaerodynamic forces are not excessive.Hydro-mechanicalThe complexity and weight of mechanical flight control systems increase considerably with thesize and performance of the aircraft. Hydraulically powered control surfaces help to overcomethese limitations.A hydro-mechanical flight control system has two parts:The mechanical circuit, which links the cockpit controls with the hydraulic circuits. Likethe mechanical flight control system, it consists of rods, cables, pulleys, and sometimeschains.The hydraulic circuit, which has hydraulic pumps, reservoirs, filters, pipes, valves andactuators. The actuators are powered by the hydraulic pressure generated by the pumps inthe hydraulic circuit. The actuators convert hydraulic pressure into control surfacemovements. The electro-hydraulic servo valves control the movement of the actuators.Fly-by-wire control systemsMain article: Fly-by-wireA fly-by-wire (FBW) system replaces manual flight control of an aircraft with an electronicinterface. The movements of flight controls are converted to electronic signals transmitted bywires (hence the fly-by-wire term), and flight control computers determine how to move theactuators at each control surface to provide the expected response. Commands from the
computers are also input without the pilots knowledge to stabilize the aircraft and perform othertasks. Electronics for aircraft flight control systems are part of the field known as avionics.Fly-by-optics, also known as fly-by-light, is a further development using fiber optic cables.AutopilotAn autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle withoutassistance from a human being. An autopilot can refer specifically to aircraft, self-steering gearfor boats, or auto guidance of space craft and missiles.Fly-by-wireFly-by-wire (FBW) is a system that replaces the conventional manual flight controls of anaircraft with an electronic interface. The movements of flight controls are converted to electronicsignals transmitted by wires (hence the fly-by-wire term), and flight control computers determinehow to move the actuators at each control surface to provide the ordered response. The fly-by-wire system also allows automatic signals sent by the aircrafts computers to perform functionswithout the pilots input, as in systems that automatically help stabilize the aircraft.