The principles of air navigation are the same for all aircraft, big or small. SMALL, Small Machine Algol Like Language is a programming language developed by Dr Air navigation involves successfully piloting an aircraft from place to place without getting lost, breaking the laws applying to aircraft, or endangering the safety of those on board or on the ground.

Air navigation differs from the navigation of surface craft in several ways:

Aircraft travel at relatively high speeds, leaving less time to calculate their position en route. Aircraft normally cannot stop in mid-air to ascertain their position at leisure. Aircraft are safety-limited by the amount of fuel they can carry; a surface vehicle can usually get lost, run out of fuel, then simply await rescue. There is no in-flight rescue for most aircraft. And collisions with obstructions are usually fatal. Therefore, constant awareness of position is critical for aircraft pilots.

The techniques used for navigation in the air will depend on whether the aircraft is flying under the visual flight rules (VFR) or the instrument flight rules (IFR). Navigation is the process of reading and controlling the movement of a craft or vehicle from one place to another In the latter case, the pilot will navigate exclusively using instruments and radio navigation aids such as beacons, or as directed under radar control by air traffic control. Most aircraft are equipped with a standard set of flight instruments which give the pilot information about the aircraft's attitude airspeed and altitude Radio navigational aids, much like Hearing aids, are small devices that allow other technological devices to receive Signals which help with navigation Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Air traffic control ( ATC) is a service provided by ground-based controllers who direct Aircraft on the ground and in the air In the VFR case, a pilot will largely navigate using dead reckoning combined with visual observations (known as pilotage), with reference to appropriate maps. Dead reckoning ( DR) is the process of estimating one's current position based upon a previously determined position or fix, and advancing that position based upon Pilotage is the use of fixed visual references on the ground or sea by means of sight or radar to guide oneself to a destination sometimes with the help of a Map or Nautical This may be supplemented using radio navigation aids.

Route planning

The first step in navigation is deciding where one wishes to go. A private pilot planning a flight under VFR will usually use an aeronautical chart of the area which is published specifically for the use of pilots. An aeronautical chart is a Map designed to assist in Navigation of Aircraft, much as Nautical charts do for watercraft or a roadmap This map will depict controlled airspace, radio navigation aids and airfields prominently, as well as hazards to flying such as mountains, tall radio masts, etc. Controlled airspace is an aviation term used to describe Airspace in which traffic levels are such that it has been determined that Air traffic control (ATC must An aerodrome is an area on land or water (including any buildings installations and equipment used for the arrival and departure of aircraft It also includes sufficient ground detail - towns, roads, wooded areas - to aid visual navigation. In the UK, the CAA publishes a series of maps covering the whole of the UK at various scales, updated annually. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located The information is also updated in the notices to airmen, or NOTAMs. NOTAM or NoTAM is the quasi- Acronym for a "Notice To Airmen"

The pilot will choose a route, taking care to avoid controlled airspace that is not permitted for the flight, restricted areas, danger areas and so on. Controlled airspace is an aviation term used to describe Airspace in which traffic levels are such that it has been determined that Air traffic control (ATC must The chosen route is plotted on the map, and the lines drawn are called the track. The aim of all subsequent navigation is to follow the chosen track as accurately as possible. Occasionally, the pilot may elect on one leg to follow a clearly visible feature on the ground such as a railway track, river, highway, or coast.

Adjustment of an aircraft's heading to compensate for wind flow perpendicular to the ground track

When an aircraft is in flight, it is moving relative to the body of air it is flying in, therefore maintaining an accurate ground track is not as easy as it might appear, unless there is no wind at all — a very rare occurrence. Therefore the pilot must adjust heading to compensate for the wind, in order to follow the ground track. The wind triangle is a graphical representation of the relationship between Aircraft motion and Wind. Initially the pilot will calculate headings to fly for each leg of the trip prior to departure, using the forecast wind directions and speeds supplied by the meteorological authorities for the purpose. These figures are generally accurate and updated several times per day, but the unpredictable nature of the weather means that the pilot must be prepared to make further adjustments in flight. A general aviation (GA) pilot will often make use of either the E6B flight computer - a type of slide rule - or a purpose designed electronic navigational computer to calculate initial headings. StudentE6BFlightComputerjpg|thumb|An E6B flight computer commonly used by student pilots The slide rule, also known as a slipstick, is a mechanical Analog computer.

The primary instrument of navigation is the magnetic compass. A compass, magnetic compass or mariner's compass is a navigational instrument for determining direction relative to the earth's Magnetic poles It consists The needle or card aligns itself to magnetic north, which does not coincide with true north, so the pilot must also allow for this, called the magnetic variation (or declination). The magnetic declination (also known as grid magnetic angle in military circles at any point on the Earth is the angle between the local magnetic field -- the direction noted by the Chinese Polymath Shen Kuo in the 11th century and possibly the egyptians over 6 millenia ago The magnetic declination (also known as grid magnetic angle in military circles at any point on the Earth is the angle between the local magnetic field -- the direction The variation that applies locally is also shown on the flight map. Once the pilot has calculated the actual headings required, the next step is to calculate the flight times for each leg. This is necessary to perform accurate dead reckoning. Dead reckoning ( DR) is the process of estimating one's current position based upon a previously determined position or fix, and advancing that position based upon The pilot also needs to take into account the slower initial airspeed during climb to calculate the time to top of climb. It is also helpful to calculate the top of descent, or the point at which the pilot would plan to commence the descent for landing.

The flight time will depend on both the desired cruising speed of the aircraft, and the wind - a tailwind will shorten flight times, a headwind will increase them. The E6B has scales to help pilots compute these easily. StudentE6BFlightComputerjpg|thumb|An E6B flight computer commonly used by student pilots

The point of no return is the point on a flight at which a plane has just enough fuel, plus any mandatory reserve, to return to the airfield from which it departed. The point of no return is the point beyond which someone or some group of people must continue on their current course of action either because turning back is physically impossible Beyond this point that option is closed, and the plane must proceed to some other destination.

Alternatively, with respect to a large region without airfields, e. g. an ocean, it can mean the point before which it is closer to turn around and after which it is closer to continue.

Additional calculations depending on the aircraft and the terrain may include single engine flight characteristics in the event of a loss of one of a twin's engines in flight.

The final stage is to note over which areas the route will go, and to make a note of all of the things to be done - which ATC units to contact, the appropriate frequencies, visual reporting points, and so on. It is also important to note which pressure setting regions will be entered, so that the pilot can ask for the QNH (air pressure) of those regions. QNH is a Q code. It is a pressure setting used by pilots, Air traffic control (ATC and Low frequency Weather beacons to refer to Finally, the pilot should have in mind some alternative plans in case the route cannot be flown for some reason - unexpected weather conditions being the most common. At times the pilot may be required to file a flight plan for an alternate destination and to carry adequate fuel for this. The more work a pilot can do on the ground prior to departure, the easier it will be in the air.

IFR planning

In many respects this is similar to VFR flight planning except that the task is generally made simpler by the use of special charts that show IFR routes from beacon to beacon with the lowest safe altitude (LSALT), bearings (in both directions) and distance marked for each route. Flight planning is the process of producing a Flight plan to describe a proposed Aircraft flight The lowest safe altitude (LSALT is a term used in Aviation and in particular in Air navigation. IFR pilots may fly on other routes but they then have to do all of these calculations themselves with the LSALT calculation being the most difficult. The pilot then needs to look at the weather and minimum specifications for landing at the destination airport and the alternate requirements. The pilot must also comply with all the rules including their legal ability to use a particular instrument approach depending on how recently they last performed one.

In flight

Once in flight, the pilot must take pains to stick to plan, otherwise getting lost is all too easy. This is especially true if flying over featureless terrain. This means that the pilot must stick to the calculated headings, heights and speeds as accurately as possible. The visual pilot must regularly compare the ground with the map, (pilotage) to ensure that the track is being followed although adjustments are generally calculated and planned. Pilotage is the use of fixed visual references on the ground or sea by means of sight or radar to guide oneself to a destination sometimes with the help of a Map or Nautical Usually, the pilot will fly for some time as planned to a point where features on the ground are easily recognised. If the wind is different from that expected, the pilot must adjust heading accordingly, but this is not done by guesswork, but by mental calculation - often using the 1 in 60 rule. The 1 in 60 rule is used in Air navigation, and states that if a pilot has travelled sixty miles then an error in track of one mile is approximately a 1° error For example a two degree error at the halfway stage can be corrected by adjusting heading by four degrees the other way to arrive in position at the end of the leg. This is also a point to reassess the estimated time for the leg. A good pilot will become adept at applying a variety of techniques to stay on track.

While the compass is the primary instrument used to determine one's heading, pilots will usually refer instead to the direction indicator (DI), a gyroscopically driven device which is much more stable than a compass. The heading indicator (Directional Gyro or DG) is an instrument used in an Aircraft to inform the pilot of his heading A gyroscope is a device for measuring or maintaining orientation, based on the principles of Angular momentum. The compass reading will be used to correct for any drift (precession) of the DI periodically. Precession refers to a change in the direction of the axis of a rotating object The compass itself will only show a steady reading when the aircraft has been in straight and level flight long enough to allow it to settle.

Should the pilot be unable to complete a leg - for example bad weather arises, or the visibility falls below the minima permitted by the pilot's license, the pilot must divert to another route. Since this is an unplanned leg, the pilot must be able to mentally calculate suitable headings to give the desired new track. Using the E6B in flight is usually impractical, so mental techniques to give rough and ready results are used. StudentE6BFlightComputerjpg|thumb|An E6B flight computer commonly used by student pilots The wind is usually allowed for by assuming that sine A = A, for angles less than 60° (when expressed in terms of a fraction of 60° - e. g. 30° is 1/2 of 60°, and sine 30° = 0. 5), which is adequately accurate. A method for computing this mentally is the clock code. The clock code is a method of mentally computing the Sine of an angle between zero and sixty degrees. However the pilot must be extra vigilant when flying diversions to maintain awareness of position.

Some diversions can be temporary - for example to skirt around a local storm cloud. In such cases, the pilot can turn 60 degrees away his desired heading for a given period of time. Once clear of the storm, he can then turn back in the opposite direction 120 degrees, and fly this heading for the same length of time. This is a 'wind-star' maneuver and, with no winds aloft, will place him back on his original track with his trip tme increased by the length of one diversion leg.

Navigation Aids

Main article: Radio navigation

Good pilots use all means available to help navigate. Radio navigation or radionavigation is the application of Radio frequencies to determining a position on the Earth. Many GA aircraft are fitted with a variety of radio navigation aids, such as Automatic direction finder (ADF), VHF omnidirectional range (VOR) and Global Positioning System (GPS). A radio direction finder ( RDF) is a device for finding the direction to a Radio source This article is about the radio navigation aid see VOR for other uses Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth

ADF uses non-directional beacons (NDBs) on the ground to drive a display which shows the direction of the beacon from the aircraft. A Non-directional beacon ( NDB) is a Radio transmitter at a known location used as an aviation or marine Navigational aid The pilot may use this bearing to draw a line on the map to show the bearing from the beacon. By using a second beacon, two lines may be drawn to locate the aircraft at the intersection of the lines. This is called a cross-cut. Alternatively, if the track takes the flight directly overhead a beacon, the pilot can use the ADF instrument to maintain heading relative to the beacon, though "following the needle" is bad practice, especially in the presence of a strong cross wind - the pilot's actual track will spiral in towards the beacon, not what was intended. NDBs also can give erroneous readings because they use very long wavelengths, which are easily bent and reflected by ground features and the atmosphere. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. NDBs continue to be used as a common form of navigation in some countries with relatively few navigational aids.

VOR is a more sophisticated system, and is still the primary air navigation system established for aircraft flying under IFR in those countries with many navigational aids. This article is about the radio navigation aid see VOR for other uses In this system, a beacon emits a specially modulated signal which consists of two sine waves which are out of phase. The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0 The phase difference corresponds to the actual bearing relative to true north that the receiver is from the station. The upshot is that the receiver can determine with certainty the exact bearing from the station. Again, a cross-cut is used to pinpoint the location. Many VOR stations also have additional equipment called DME (distance measuring equipment) which will allow a suitable receiver to determine the exact distance from the station. Distance Measuring Equipment (DME is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals Together with the bearing, this allows an exact position to be determined from a single beacon alone. For convenience, some VOR stations also transmit local weather information which the pilot can listen in to, perhaps generated by an Automated Surface Observing System. Automated airport weather stations are automated sensor suites which are designed to serve Aviation and meteorological observing needs for safe and efficient

Prior to the advent of GPS, Celestial Navigation was also used by trained navigators on military bombers and transport aircraft in the event of all electronic navigational aids being turned off in time of war. Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth Celestial navigation, also known as astronavigation, is a Position fixing technique that was devised to help sailors cross the featureless oceans without having to Originally navigators used an astrodome and regular sextant but the more streamlined periscopic sextant was used from the 1940s to the 1990s. This article is about the sextant as used for Navigation. For the astronomer's sextant, see Sextant (astronomical.

Finally, an aircraft may be supervised from the ground using radar. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships ATC can then feed back information to the pilot to help establish position, or can actually tell the pilot the position of the aircraft, depending on the level of ATC service the pilot is receiving. Air traffic control ( ATC) is a service provided by ground-based controllers who direct Aircraft on the ground and in the air

The use of GPS navigation in aircraft is becoming increasingly common. GPS provides very precise aircraft position, altitude, heading and ground speed information. GPS makes navigation precision once reserved to large RNAV-equipped aircraft available to the GA (general aviation) pilot. Area Navigation (RNAV is a method of Air navigation that allows an aircraft to choose any course within a network of navigation beacons rather than navigating directly to and General aviation (abbr GA) is one of two categories of Civil aviation. Recently, more and more airports include GPS instrument approaches. GPS approaches consist of either overlays to existing non-precision approaches or stand-alone GPS non-precision approaches.

See also

• ADS-B
• Aeronautical chart
• Air safety
• RAIM
• Great-circle distance
• ETOPS/LROPS
• Flight instruments
• Flight management system
• Flight planning
• Instrument Landing System
• Air traffic obstacle
• Radio navigation
• SIGI
• Spherical trig
• transatlantic flight
• Wind triangle

External links

• Fly Away - Air Navigation tutorials