ALTIMETER1. Barometric Altimeter

QNH QFE QNE

2. Radar altimeter

RADIORADAR

Invented In 1924 by Lloyd ESPENSCHIED

In 1938, in cooperation with Bell Labs, United Air Lines used it as a terrain avoidance device

RADAR ALTIMETER

Provides distance between plane and ground below it

RADIO ALTIMETER

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Measures altitude above the terrain

LRRA

RA

DH Annunciator

Decision Height Bug

Failure Warning Flag

Altitude Pointer

TEST Push Button

DH SET Knob

COMPONENTS

Accuracy: ± (3%+5’) in landing attitudeFrequency: 4200-4400MHz It uses SHF band

Antenna has a lobe of about 80°

It can detect height correctly up to bank angles of about 40°

For landing as pitch and roll do not normally exceed 20°

Radar Altimeter Antenna

METHODS USE IN RADAR ALTIMETRY

• Radiation consists of a series of discrete pulses• By transmitting radio waves downward• Interpreting the time it takes for the waves to reflect

back

• Sends out a continuous transmission wave• Distance = size of shift in signal's frequency• The greater the shift the further the distance

travelled• Ground proximity warning

1.PULSE MODULATED RADAR

2.FMCW

OPERATION

• It is a CW radar system • Separate transmit and receive antennas• Single antenna is not reliable

Principle Of Radar Altimeter

• Frequency modulated continuous wave

• It uses the principle of RADAR

• Speed, distance and time are related

• S=VT• Radio waves are transmitted towards the ground and

the time it takes them to be reflected back and return to the aircraft is timed

Military Applications1 To fly quite low over

the land and the seaTo avoid radar detection To avoid targeting by anti-aircraft guns

To avoid surface-to-air missiles

Terrain-following radar, which allows fighter bombers to fly at extremely low altitudesIn modern fighter aircrafts, forward terrain looking radars are also used F/A-18 Super Hornet warplanes flown by the Americans and by the Australians

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For approach and landing

In low-visibility conditions

In automatic landings

Allowing the autopilot to know when to begin the flare maneuver Radar Altimeters give data to the auto throttle

Give readings up to 2,500 feet (AGL)

Almost all airliners are equipped with radar altimeters

Concorde and the British Aircraft Corporation BAC 1-11

ATR 42 and BAE Jetstream series)

1Civil Application

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