Wednesday, November 12, 2008

Aviation light signals

From Wikipedia, the free encyclopedia

In the case of a radio failure or aircraft not equipped with a radio, air traffic control may use a signal lamp to direct the aircraft. The signal lamp has a focused bright beam and is capable of emitting three different colors: red, white and green. These colors may be flashed or steady, and have different meanings to aircraft in flight or on the ground. Planes can acknowledge the instruction by wiggling their wings, moving the ailerons if on the ground, or by flashing their landing or navigation lights during hours of darkness.


Aircraft in flight Aircraft on the ground Ground vehicles or personnel
Flashing white N/A Return to starting point Return to starting point
Steady green Cleared to land Cleared for takeoff Cleared to cross/proceed
Flashing green Cleared to approach airport, or return to land Cleared to taxi N/A
Steady red Continue circling, give way to other aircraft Stop Stop
Flashing red Airport unsafe, do not land Immediately taxi clear of runway in use Clear the taxiway/runway
Alternating red and green Exercise extreme caution Exercise extreme caution Exercise extreme caution
Blinking runway lights Vehicles, planes, and pedestrians immediately clear landing area in use

Friday, November 7, 2008

Great-circle distance

From Wikipedia, the free encyclopedia
The great-circle distance is the shortest distance between any two points on the surface of a sphere measured along a path on the surface of the sphere (as opposed to going through the sphere's interior). Because spherical geometry is rather different from ordinary Euclidean geometry, the equations for distance take on a different form. The distance between two points in Euclidean space is the length of a straight line from one point to the other. On the sphere, however, there are no straight lines. In non-Euclidean geometry, straight lines are replaced with Geodesics. Geodesics on the sphere are the great circles (circles on the sphere whose centers are coincident with the center of the sphere).

Between any two points on a sphere which are not directly opposite each other, there is a unique great circle. The two points separate the great circle into two arcs. The length of the shorter arc is the great-circle distance between the points. A great circle endowed with such a distance is the Riemannian circle.

Between two points which are directly opposite each other, called antipodal points, there are infinitely many great circles, but all great circle arcs between antipodal points have the same length, i.e. half the circumference of the circle, or πr, where r is the radius of the sphere.

Because the Earth is approximately spherical (see Earth radius), the equations for great-circle distance are important for finding the shortest distance between points on the surface of the Earth (as the crow flies), and so have important applications in navigation.

The geographical formula

Let \phi_s,\lambda_s;\ \phi_f,\lambda_f\;\! be the geographical latitude and longitude of two points (a base "standpoint" and the destination "forepoint"), respectively, and \Delta\phi,\Delta\lambda\;\! their differences and \Delta\widehat{\sigma}\;\! the (spherical) angular difference/distance, or central angle, which can be constituted from the spherical law of cosines:

{\color{white}\Big|}\Delta\widehat{\sigma}=\arccos\big(\cos\phi_s\cos\phi_f\cos\Delta\lambda+\sin\phi_s\sin\phi_f\big).\;\!

The distance d, i.e. the arc length, for a sphere of radius r and \Delta\widehat{\sigma}\! given in radians, is then:

d = r \Delta\widehat{\sigma}.

This arccosine formula above can have large rounding errors for the common case where the distance is small, however, so it is not normally used. Instead, an equation known historically as the haversine formula was preferred, which is much more accurate for small distances:[1]

{\color{white}\frac{\bigg|}{|}}\Delta\widehat{\sigma} =2\arcsin\left(\sqrt{\sin^2\left(\frac{\Delta\phi}{2}\right)+\cos{\phi_s}\cos{\phi_f}\sin^2\left(\frac{\Delta\lambda}{2}\right)}\right).\;\!

(Historically, the use of this formula was simplified by the availability of tables for the haversine function: hav(θ) = sin2(θ/2).)

Although this formula is accurate for most distances, it too suffers from rounding errors for the special (and somewhat unusual) case of antipodal points (on opposite ends of the sphere). A more complicated formula that is accurate for all distances is the Vincenty formula: [2]

{\color{white}\frac{\bigg|}{|}|}\Delta\widehat{\sigma}=\arctan\left(\frac{\sqrt{\left(\cos\phi_f\sin\Delta\lambda\right)^2+\left(\cos\phi_s\sin\phi_f-\sin\phi_s\cos\phi_f\cos\Delta\lambda\right)^2}}{\sin\phi_s\sin\phi_f+\cos\phi_s\cos\phi_f\cos\Delta\lambda}\right);\;\!

(When programming a computer, one should use the atan2() function rather than the ordinary arctangent function (atan()), in order to simplify handling of the case where the denominator is zero.)

If r is the great-circle radius of the sphere, then the great-circle distance is r\,\Delta\widehat{\sigma}\;\!.

Note: above, accuracy refers to rounding errors only; all formulas themselves are exact (for a sphere).

Radius for spherical Earth

See also: Earth radius

The shape of the Earth closely resembles a flattened spheroid with extreme values for the radius of 6,378.137 km at the equator and 6,356.752 km at the poles. The average radius for a spherical approximation of the figure of the Earth is approximately 6371.01 km (3958.76 statute miles, 3440.07 nautical miles).

A worked example

In order to use this formula for anything practical you will need two sets of coordinates. For example, the latitude and longitude of two airports:

  • Nashville International Airport (BNA) in Nashville, TN, USA: N 36°7.2', W 86°40.2'
  • Los Angeles International Airport (LAX) in Los Angeles, CA, USA: N 33°56.4', W 118°24.0'

First, convert these coordinates to decimal degrees (Sign × (Deg + (Min + Sec / 60) / 60)) and radians (× π / 180) before you can use them effectively in a formula. After conversion, the coordinates become:

  • BNA: \phi_s= 36.12^\circ\approx 0.6304\mbox{ rad};\;\;\lambda_s=-86.67^\circ\approx -1.5127\mbox{ rad};\;\!
  • LAX: \phi_f= 33.94^\circ\approx 0.5924\mbox{ rad};\;\;\lambda_f=-118.40^\circ\approx -2.0665\mbox{ rad};\;\!

Using these values in the angular difference/distance equation:

r\,\Delta\widehat{\sigma}\approx 6371.01\times0.45306 \approx 2886.45\mbox{ km}.\;\!

Thus the distance between LAX and BNA is about 2886 km or 1794 miles (× 0.62137) or 1557 nautical miles (× 0.539553).

See also

References

  1. ^ R.W. Sinnott, "Virtues of the Haversine", Sky and Telescope, vol. 68, no. 2, 1984, p. 159
  2. ^ Vincenty, Thaddeus (1975-04-01). "Direct and Inverse Solutions of Geodesics on the Ellipsoid with Application of Nested Equations" (PDF). Survey Review 23 (176): 88–93. Kingston Road, Tolworth, Surrey: Directorate of Overseas Surveys. Retrieved on 2008-07-21.

External links

Air navigation

From Wikipedia, the free encyclopedia

The principles of air navigation are the same for all aircraft, big or small. 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). 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. In the VFR case, a pilot will largely navigate using dead reckoning combined with visual observations (known as pilotage), with reference to appropriate maps. 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. 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. 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 information is also updated in the notices to airmen, or NOTAMs.

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. 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. 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.

The primary instrument of navigation is the magnetic compass. 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 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. 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.

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. 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.

With regards to the "Point of NO return" or what is sometimes referred to as the ETP(Equal time Point). The aricraft that is flying across the Ocean for example, would be required to calculate ETPs for single engine, depressurization, and a normal ETP. All of which could actually be different points along the route. For example, single engine and depressurization situations the aircraft would be forced to lower operational altitudes, which would effect their fuel burn, cruise speed and ground speed. Each situation therefore would have a different ETP.

Commercial aircraft are not allowed to operate along a route with what is known as a wet foot print. So the ETP calculations serves as a planning stategy, so flight crews always have an out in a emergency event. Allowing a safe return to there chosen alternate.

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. 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. 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. 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. 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 compass reading will be used to correct for any drift (precession) of the DI periodically. 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. 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. 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. Many GA aircraft are fitted with a variety of radio navigation aids, such as Automatic direction finder (ADF), VHF omnidirectional range (VOR) and GNSS.

ADF uses non-directional beacons (NDBs) on the ground to drive a display which shows the direction of the beacon from the aircraft. 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. 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. In this system, a beacon emits a specially modulated signal which consists of two sine waves which are out of phase. 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. 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.

Prior to the advent of GNSS, 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. Originally navigators used an astrodome and regular sextant but the more streamlined periscopic sextant was used from the 1940s to the 1990s.

Finally, an aircraft may be supervised from the ground using surveilance information from e.g. radar or multilateration. 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.

The use of GNSS in aircraft is becoming increasingly common. GNSS provides very precise aircraft position, altitude, heading and ground speed information. GNSS makes navigation precision once reserved to large RNAV-equipped aircraft available to the GA pilot. Recently, more and more airports include GNSS instrument approaches. GNSS approaches consist of either overlays to existing non-precision approaches or stand-alone GNSS non-precision approaches.

See also

External links

Instrument approach

From Wikipedia, the free encyclopedia
Terminal procedures for an ILS approach in the United States. (The disclaimers shown in red in the illustration do not appear on the original approach plate.)

An instrument approach or instrument approach procedure (IAP) is a type of air navigation that allows pilots to land an aircraft in reduced visibility (known as instrument meteorological conditions or IMC), or to reach visual conditions permitting a visual landing.

Approaches are classified as either precision or nonprecision, depending on the accuracy and capabilities of the navigational aids (navaids) used. Precision approaches utilize both lateral (localizer) and vertical (glideslope) information. Nonprecision approaches provide lateral course information only.

The publications depicting instrument approach procedures are called Terminal Procedures, but are commonly referred to by pilots as "approach plates". These documents graphically depict the specific procedure to be followed by a pilot for a particular type of approach to a given runway. They depict prescribed altitudes and headings to be flown, as well as obstacles, terrain, and potentially conflicting airspace. In addition, they also list missed approach procedures and commonly-used radio frequencies.

Basic principles

Instrument approaches are generally designed such that a pilot of an aircraft in instrument meteorological conditions (IMC), by the means of radio, GPS or INS navigation with no assistance from air traffic control, can navigate to the airport, hold in the vicinity of the airport if required, then fly to a position from where he or she can obtain sufficient visual reference of the runway for a safe landing to be made, or execute a missed approach if the visibility is below the minimums required to execute a safe landing. The whole of the approach is defined and published in this way so that aircraft can land if they suffer from radio failure; it also allows instrument approaches to be made procedurally at airports where air traffic control does not use radar or in the case of radar failure.

Instrument approaches generally involve five phases of flight:

  • Arrival: where the pilot navigates to the Initial Approach Fix (IAF: a navaid or reporting point), and where holding can take place.
  • Initial Approach: the phase of flight after the IAF, where the pilot commences the navigation of the aircraft to the Final Approach Fix (FAF), a position aligned with the runway, from where a safe controlled descent back towards the airport can be initiated.
  • Intermediate Approach: an additional phase in more complex approaches that may be required to navigate to the FAF.
  • Final approach: between 4 and 12 nms of straight flight descending at a set rate (usually an angle of between 2.5 and 6 degrees).
  • Missed Approach: an optional phase; should the required visual reference for landing not have been obtained at the end of the final approach, this allows the pilot to climb the aircraft to a safe altitude and navigate to a position to hold for weather improvement or from where another approach can be commenced.

When aircraft are under radar control, air traffic controllers may replace some or all of these phases of the approach with radar vectors (the provision of headings on which the controller expects the pilot to navigate his aircraft) to the final approach, to allow traffic levels to be increased over those of which a fully procedural approach is capable. It is very common for air traffic controllers to vector aircraft to the final approach aid, e.g. the ILS, which is then used for the final approach. In the case of the rarely-used Ground-Controlled Approach (GCA), the instrumentation (normally Precision Approach Radar) is on the ground and monitored by a controller, who then relays precise instructions for adjustment of heading and altitude to the pilot in the approaching aircraft.

Low visibility approaches

Many instrument approaches allow for landing in conditions of low visibility. ICAO classifies ILS approaches as being in one of the following categories:

ILS Categories
Category Decision Height (above threshold) RVR limit
I greater than 200 ft 550m or 1800 ft
II less than 200 ft 350m or 1200 ft
IIIa less than 100 ft 150m - 200m (see below)
IIIb less than 50 ft 75m - 150m (see below)
IIIc No DH No RVR

Cat III mimima depend on Roll Out Control & Redundancy of the Autopilot.

Low visibility approaches are those in categories II and III.

For larger aircraft it is typical that these approaches are under the control of the flight control system with the flight crew providing a supervisory role.

Traditionally smaller aircraft which lacked redundancy in the flight control systems could not fly these approaches. (Imagine a radio getting a glitch at the moment of flare which causes the airplane to "think" that a large correction is required. The result would, most likely, be a sudden turn which at low altitude would be catastrophic.) A Head-Up Display allows the flight crew to fly the aircraft using the guidance cues from the ILS sensors so that if such a large deviation were seen, the pilot would be able to respond in an appropriate and safe manner. This is becoming increasingly popular with "feeder" airlines and most manufactures of regional jets are now offering HUDs as either standard or optional equipment. In addition a HUD can provide a low visibility take off capability.

For both automatic and HUD landing systems, the equipment requires special approval for its design and also for each individual installation. The design takes into consideration all of the additional safety requirements for operating an aircraft in close proximity to the ground and takes into consideration the ability of the flight crew to react to a "system anomaly." Once installed, the equipment also has additional maintenance requirements to ensure that it is fully capable of supporting reduced visibility operations.

In all cases, additional crew training is required for such approaches, and a certain number of low visibility approaches must either be performed or simulated in a set period of time for pilots to stay 'current' in performing them.

For practical reasons Category IIIc approaches are rare, but category IIIb approaches are relatively common at major airports.

There are also air traffic control considerations with low visibility approaches: when using ILS, the integrity of the signal must be protected, which requires that certain areas of the airport close to the installations being free of other aircraft and vehicles. Also there must be bigger gaps between aircraft on final approach to both protect the ILS signal and to cope with slower runway vacation times. In addition, the airport itself has special considerations for low visibility operations including different lighting for approach, runways, and taxiways as well as the location of emergency equipment.

Precision approaches and systems

  • ILS - Instrument Landing System
  • MLS - Microwave Landing System
  • PAR - Precision Approach Radar (Military)
  • GPS (with vertical navigation via WAAS or EGNOS) - Global Positioning System
  • LAAS - Ground Based Augmentation System (GBAS) for Global Satellite Navigation Systems (GNSS)
  • JPALS - Joint Precision Approach and Landing System
  • GCA - Ground-Controlled Approach (mostly military)

Nonprecision approaches and systems

Terminology

Decision Height or Altitude

A decision height (DH) or decision altitude (DA) is a specified height or altitude in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been acquired. This allows the pilot sufficient time to safely re-configure the aircraft to climb and execute the missed approach procedures while avoiding terrain and obstacles.

Minimum Descent Height or Altitude

A minimum descent height (MDH) or minimum descent altitude (MDA) is the equivalent of the DA for non-precision approaches, however there are some significant differences. It is the level below which a pilot making such an approach must not allow his or her aircraft to descend unless the required visual reference to continue the approach has been established. Unlike a DA, a missed approach need not be initiated once the aircraft has descended to the MDH, that decision can be deferred to the missed approach point (MAP). So a pilot flying a non-precision approach may descend to the minimum descent altitude and maintain it until reaching the MAP, then initiate a missed approach if the required visual reference was not obtained. An aircraft must not descend below the MDH until visual reference is obtained, which differs from a DH in that an aircraft may descend below DH without visual reference so long as the missed approach procedure was initiated at or prior to the DH. For example, with a DH of 500ft AMSL, it is legal for a pilot to allow the aircraft to descend to 450ft AMSL if the missed approach procedure was initiated at or prior to 500ft. This would not be legal during a non-precision approach with a MDH of 500ft. This difference is due to the presence of vertical guidance during a precision approach, and thus terrain clearance near DH being less of an issue than near MDH during a non-precision approach.

If a runway has both precision and non-precision approaches defined, the MDA of the non-precision approach is almost always greater than the DA of the precision approach, due to the lack of vertical guidance of the non-precision approach: the actual difference will also depend on the accuracy of the navaid upon which the approach is based, with ADF approaches and SRAs tending to have the highest MDAs.

Straight-in Approach

A straight in instrument approach is one where the final approach is begun without first having executed a procedure turn, not necessarily completed with a straight-in landing or made to straight-in landing minimums.

Circling To Land

A circle to land maneuver is a maneuver used when a runway is not aligned to within 30 degrees of the track of the instrument approach procedure or the final approach requires 400 feet of descent (or more) per nautical mile, and therefore requires some visual maneuvering of the aircraft in the vicinity of the airport after the instrument portion of the approach is completed for the aircraft to become aligned with the runway to land.

It's very common for a circle to land maneuver be executed during a straight-in approach to a different runway, e.g. an ILS approach to one runway, followed by a low-altitude pattern flying, ending in a landing on a different runway. This way, approach procedures to one runway can be used to land on any runway at the airport, as the other runways may lack instrument procedures or their approaches cannot be used for other reasons (traffic considerations, navigation aids being out of service, etc).

Circling to land is considered more difficult and less safe than a straight-in landing, especially under Instrument meteorological conditions.

Instrument Currency

In some countries Instrument Rated Pilots are required to perform a minimum number of instrument approaches in a set period to remain current. Pilots may also have to fly a certain number of low visibility approaches (Cat 2 or Cat 3) to remain current at performing these. When practicing instrument approaches in visual meteorological conditions, a safety pilot is required. This is because the pilot practicing instrument approach must wear a view limiting device, which restricts his field of view to the instrument panel. A safety pilot's basic role is to observe and help to avoid traffic.

Airport Requirements

The requirements for an airport to offer instrument approaches is contained in FAA Order 8200.97 AIRMAN AND AIRCRAFT APPROVAL FOR REDUCED VISIBILITY FLIGHT OPERATIONS, INCLUDING CATEGORY II/III OPERATIONS.

References

Audio and Multimedia Resources

Aeronautical chart

From Wikipedia, the free encyclopedia

An aeronautical chart is a map designed to assist in navigation of aircraft, much as nautical charts do for watercraft, or a roadmap for drivers. Using these charts and other tools pilots are able to determine their position, safe altitude, best route to a destination, navigation aids along the way, alternative landing areas in case of an in-flight emergency, and other useful information such as radio frequencies and airspace boundaries. There are charts for all land masses on Earth, and long-distance charts for trans-oceanic travel.

Specific charts are used for each phase of a flight and may vary from a map of a particular airport facility to an overview of the instrument routes covering an entire continent (e.g., global navigation charts), and many types in between.

Charts for visual flight rules (VFR)

Under "visual flight rules", pilots are expected to see and avoid dangers along the way (obstacles, other aircraft, bad weather, etc), and to use pilotage and other means for navigating. VFR charts include a large amount of information describing the local topography, not the least of which is the elevation. Standardized symbols are used for indication of land and water features such as mountains, shorelines and rivers. Roads, towns and other identifiable features may also be shown, in addition to specific aeronautical details.

Visual flight charts are divided into categories, depending upon their scale, which is proportional to the size of the area covered by one map. The amount of detail is necessarily reduced when larger areas are covered with a map having a compact scale.

  • World aeronautical charts (WACs) have a scale of 1:1,000,000 and cover relatively large areas. Outside of WAC coverage, operational navigation charts (ONC) may be used, having the same scale as WACs.
  • Sectional charts typically cover a few hundred square miles of area (1:500,000).
  • VFR Terminal area charts are created with a scale and coverage appropriate for the general vicinity of a large airport (1:250,000). They may depict preferred VFR flight routes within areas of congested airspace.

Charts for instrument flight rules (IFR)

Instrument flight requires the use of artificial aids to navigation, under the control of an air traffic controller, usually based upon a flight plan. The charts used for IFR flights contain an abundance of information regarding locations (waypoints) "fix" according to measurements from electronic beacons of various types, as well as the routes connecting these waypoints. Only limited topographic information is found on IFR charts.

En-route low and high altitude charts are published with a scale that depends upon the density of navigation information required in the vicinity.

Information from IFR charts is often programmed into an flight management system or autopilot system, which may simplify many of the tasks involved in following (or deviating from) a flight plan.

Terminal procedure publications such as Standard Terminal Arrival plates, Standard Instrument Departure plates, and other documentation provide detailed information for arrival, departure and taxiing at each approved airport having instrument capabilities of some sort.

Sources for charts

Aeronautical charts may be purchased at fixed base operators (FBOs), internet supply sources, or catalogs of aeronautical gear. They may also be viewed online from sources such as Skyvector and the FAA.

See also

Air Defense Identification Zone (ADIZ)

From Wikipedia, the free encyclopedia

An air defense identification zone (ADIZ) is an area of airspace defined by a nation within which "the ready identification, the location, and the control of aircraft are required in the interest of national security"[1]. Typically, an aircraft entering an ADIZ is required to radio its planned course, destination, and any additional details about its trip through the ADIZ to a higher authority, typically an air traffic controller.

An ADIZ may be in airspace over the sovereign land or sea territory of a state, for example over a military installation or over the state's territorial waters, in which case it is simply an internal administrative matter, based on the principal of national sovereignty over airspace.

The United States and certain other nations including Canada, Australia, Japan, and Iceland, however, have established self-declared air defense identification zones extending hundreds of miles over maritime areas beyond their territorial waters, without an explicit basis in international law.

North America

In North America, the United States and Canada are surrounded by an ADIZ, which is jointly administered by the civilian air traffic control authorities and the militaries of both nations, under the auspices of the North American Aerospace Defence Command or NORAD. (The Canadian ADIZ when discussed separately is known as the Canadian Air Defence Identification Zone or CADIZ.)

The joint US/Canadian ADIZ, which is almost exclusively over water, serves as a national defense boundary for aerial incursions. Any aircraft that wishes to fly in or through the boundary must file either a Defense Visual Flight Rules (DVFR) flight plan or an Instrument Flight Rules (IFR) flight plan before crossing the ADIZ. The aircraft must have an operational radar transponder and maintain two-way radio contact while approaching and crossing the North American ADIZ.

In the United States, the FAA handles the requests of international aircraft and Transport Canada handles Canadian requests. Any aircraft flying in these zones without authorization may be identified as a threat and treated as an enemy aircraft, potentially leading to interception by fighter aircraft.

The exact nature of the external ADIZ claim of the United States is unclear.

The U.S. Code of Federal Regulations Title 14 § 99.11(a)[1] states "No person may operate an aircraft into, within, or from a departure point within an ADIZ, unless the person files, activates, and closes a flight plan with the appropriate aeronautical facility, or is otherwise authorized by air traffic control", which appears to claim authority over all aircraft in the external U.S. ADIZ regardless of destination.

However, the U.S. Navy's Commander's Handbook on the Law of Naval Operations[2] states the ADIZ applies only to commercial aircraft intending to enter U.S. sovereign airspace, with a basis in international law of "the right of a nation to establish reasonable conditions of entry into its territory". The manual specifically instructs U.S. military aircraft to ignore the ADIZ of other states when operating in coastal areas:

The United States does not recognize the right of a coastal nation to apply its ADIZ procedures to foreign aircraft not intending to enter national airspace nor does the United States apply its ADIZ procedures to foreign aircraft not intending to enter U.S. airspace. Accordingly, U.S. military aircraft not intending to enter national airspace should not identify themselves or otherwise comply with ADIZ procedures established by other nations, unless the United States has specifically agreed to do so.

Meanwhile in actual practice the U.S. does attempt to apply its external ADIZ to military aircraft which pass through its extended ADIZ without intending to enter U.S. sovereign territory[3]. A U.S. Air Force university dissertation states[4]:

These regulations do not pertain to military aircraft, but to enter US airspace, without inducing the scrambling of fighter interceptors, these rules must be complied with and followed. The US does not claim sovereignty over these zones per se, but does closely monitor and request information of all objects entering the zone.

Washington D.C.

One of the most well-known recent additions to the collection of North American ADIZs is the Washington, DC Air Defense Identification Zone, which was created after the September 11, 2001 attacks by Al-Qaeda. The attacks, which used commercial airliners in large-scale suicide attacks, caused an increase in airborne security measures, including the establishment of the new ADIZ.

References