Explica§£o ILS

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ILS

Text of Explica§£o ILS

ILSILS ou Instrument Landing System um sistema de aproximao por instrumentos, que d uma orientao precisa ao avio que esteja pousando em determinada pista. Ele consiste em dois sistemas distintos, um deles mostra a orientao lateral do avio em relao a pista, e o outro mostra o ngulo de descida, ou orientao vertical. Sistema baseado na transmisso de sinais de rdio que so recebidos, processados e apresentados nos instrumentos de bordo do avio. A aproximao ILS (Instrument Landing System) tambm chamada de Aproximao de Preciso (Precision Approach), por contar com as informaes do Localizador em VHF (Very High Frequency) e do Glide Slope em UHF (Ultra High Frequency), fornecendo informaes para o alinhamento com o eixo da pista e com a trajetria correta de planeio para o pouso.

LocalizadorA antena do Localizador est situada a 1.000 ft aps a cabeceira oposta a qual estamos executando a aproximao, emitindo sinal de rdio modulado em 90 Hz e 150 Hz, separados exatamente no alinhamento da pista, com um alcance aproximado de 25 NM e at 10 para cada lado deste eixo. Tem como finalidade fornecer a direo da pista. Ao selecionarmos a freqncia do Localizador, todo o sistema de Rdio entra junto automaticamente.

Glide SlopeA antena do Glide Slope est localizada entre 750 e 1.250 ft da cabeceira da pista, e tem a finalidade de fornecer o ngulo de planeio correto durante uma aproximao. Este ngulo ideal est entre 2 e 4 e varia conforme o relevo do setor de aproximao.

MarcadoresAlgumas instalaes possuem os Marcadores junto com o ILS. Quando o avio recebe a transmisso de um marcador, um sinal visual mostrado ao piloto e outro sonoro reproduzido, operado numa freqncia de 75 MHz, cuja finalidade fornecer informaes de distancia em relao a cabeceira da pista. Marcador Externo Fica localizado a aproximadamente 7200 m (3.9 NM) da pista. Seu mdulo so duas barras por segundo com uma frequencia de 400Hz e seu indicador azul. Marcador Mdio Fica localizado a aproximadamente 1050 m da pista. Seu mdulo so barras e pontos alternados com uam frequencia de 1300Hz. Tem o propsito de avisar o piloto que o contato visual com a pista iminente.

Marcador Interno Fica localizado a aproximadamente 300 m da pista. Tem o propsito de avisar o piloto, quando em condies de baixa visibilidade, da chegada iminente a pista. Seu mdulo 6 pontos por segundo na frequencia de 3000Hz.

Categorias

Categoria I - Uma aproximao por instrumento de preciso e pouso com uma altura de deciso no menor que 60 m (200 ps) e visibilidade no menor que 800m ou contato visual com a pista no menor que 550 m. Categoria II - Uma aproximao por instrumento de preciso e pouso com uma altura de deciso menor que 60 m (200 ps) mas no menor que 30 m (100 ps), e contato visual coma pista no menor que 350 m. Categoria III possui sub-divises o Categoria III A - Uma aproximao por instrumento de preciso e pouso com uma altura de deciso menor que 30 m (100 ps), ou nenhuma altura de deciso e contato visual com a pista no menor que 200 m. o Categoria III B - Uma aproximao por instrumento de preciso e pouso com uma altura de deciso menor que 15 m (50 ps), ou nenhuma altura de deciso e contato visual com a pista menor que 200 m mas no menor que 50 m. o Categoria III C - Uma aproximao por instrumento de preciso e pouso sem altura de deciso e sem restries de visual da pista.

Uma aproximao Categoria I pode ser efetuada manualmente; nas categorias II e III requerido o uso do Piloto Automtico sendo que, para operar na Categoria III, ele tem que ter capacidade de efetuar o pouso automtico. recomendado, entretanto, que o pouso automtico seja usado tambm na Categoria II.

Instrument landing system

The Localizer station for runway 27R at Hanover/Langenhagen International Airport in Hanover, Germany. The Instrument landing system (ILS) is a ground-based instrument approach system which provides precise guidance to an aircraft approaching a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during Instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow. Instrument Approach Procedure charts (or "approach plates") are published for each ILS, providing pilots with the needed information to fly an ILS approach during Instrument flight rules (IFR) operations, including the radio frequencies used by the ILS components or navaids and the minimum visibility requirements prescribed for the specific ILS.

Principle of operationAn ILS consists of two independent sub-systems, one providing lateral guidance (Localizer), the other vertical guidance (Glideslope or Glide Path) to aircraft approaching a runway. Aircraft guidance is provided by the ILS receivers in the aircraft by performing a modulation depth comparison. The ILS has also been referred to as a Modulation Depth Comparison Navigational Aid or MDCNA.

The emission patterns of the localizer and glideslope signals. Note that the glideslope beams are partly formed by the reflection of the glideslope aerial in the ground plane. A localizer (LOC, or LLZ in Europe) antenna array is normally located beyond the departure end of the runway and generally consists of several pairs of directional antennas. Two signals are transmitted on a carrier frequency between 108.10 MHz and 111.975 MHz. One is modulated at 90 Hz, the other at 150 Hz and these are transmitted from separate but co-located antennas. Each antenna transmits a fairly narrow beam, one slightly to the left of the runway centerline, the other to the right. The localizer receiver on the aircraft measures the Difference in the Depth of Modulation (DDM) of the 90 Hz and 150 Hz signals. For the localizer, the depth of modulation for each of the modulating frequencies is 20 percent. The difference between the two signals varies depending on the position of the approaching aircraft from the centerline. If there is a predominance of either 90Hz or 150Hz modulation, the aircraft is off the centerline. In the cockpit, the needle on the Horizontal Situation Indicator, or HSI (The Instrument part of the ILS), will show that the aircraft needs to fly left or right to correct the positional error to fly down the center of the runway. If the DDM is zero the receiver aerial and therefore, the aircraft, is on the centerline of the localizer coinciding with the physical runway centerline. A glideslope or Glidepath (GP) antenna array is sited to one side of the runway touchdown zone. The GP signal is transmitted on a carrier frequency between 329.15 and 335 MHz using a technique similar to that of the localizer. The centerline of the glideslope signal is arranged to define a glideslope of approximately 3 above horizontal (ground level). Localizer and glideslope carrier frequencies are paired so that only one selection is required to tune both receivers.

These signals are displayed on an instrument in the cockpit. The pilot controls the aircraft so that the indications on the instrument remain centered on the display. This ensures the aircraft is following the ILS centreline. Some aircraft possess the ability to route signals into the autopilot, which allows the approach to be flown automatically by the autopilot.

Localizer

Localizer array and approach lighting at Whiteman Air Force Base, Johnson County, Missouri. In addition to the previously mentioned navigational signals, the localizer provides for ILS facility identification by periodically transmitting a 1020 Hz morse code identification signal. For example, the ILS for runway 04R at John F. Kennedy International Airport transmits IJFK to identify itself to users whereas runway 04L is known as IHIQ. This lets users know the facility is operating normally and that they are tuned to the correct ILS. The glideslope transmits no identification signal and therefore airborne ILS equipment relies on the localizer for identification. Modern localizer antennas are highly directional. However, usage of older, less directional antennas allows a runway to have a non-precision approach called a localizer back course. This lets aircraft land using the signal transmitted from the back of the localizer array. This signal is reverse sensing so a pilot may have to fly opposite the needle indication (depending on the equipment installed in the aircraft). Highly directional antennas do not provide a sufficient signal to support a backcourse. In the United States, backcourse approaches are commonly associated with Category I systems at smaller airports that do not have an ILS on both ends of the primary runway.

Marker beacons

The NDB station co-located with Middle Marker of Beijing Capital International Airport ILS RWY36L Main article: Marker beacon On most installations marker beacons operating at a carrier frequency of 75 MHz are provided. When the transmission from a marker beacon is received it activates an indicator

on the pilot's instrument panel and the modulating tone of the beacon is audible to the pilot. The correct height the aircraft should be at when the signal is received in an aircraft is promulgated.

Outer markerThe outer marker should be located 7.2 km (3.9 NM) from the threshold except that, where this distance is not practicable, the outer marker may be located between 6.5 and 11.1 km (3.5 and 6 NM) from the threshold. The modulation is repeated Morse-style dashes of a 400 Hz tone. The cockpit indicator is a blue lamp that flashes in unison with the received audio code. The purpose of this beacon is to provide height, distance and equipment functioning checks to aircraft on intermediate and final approach. In the United States, an NDB is often combined with the outer marker beacon in the ILS approach (called a Locator Outer Marker, or LOM); in Canada, low-powered NDBs have replaced marker beacons entirely.