RA system - component location – 1

RADIO ALTIMETER SYSTEM – INTRODUCTION

General

The radio altimeter (RA) system measures the vertical distance from the airplane to the ground. The radio altitude shows in the flight compartment on the display units (DU). The radio altitude is computed with the receiver transmitter unit by comparing the transmitted signal to the received signal. The R/T unit transmits a radio signal then receives the reflected RF signal back from the ground to determine the altitude of the aircraft. The R/T sends computed altitude data out on two ARINC 429 data buses to user systems on the aircraft.

The flight crew and other airplane systems use the altitude data during low altitude flight, approach, and landing.

The system has a range of -12 to 2500 feet.

An adjustable radio minimums alert operates with the radio altitude system and is independently selectable from 0 to 999 feet on the captains and first officers EFIS control panels. The radio minimums altitude selection is compared and processed in the display electronics units (DEUs) with the existing radio altitude value output from the radio altitude R/T. When the airplane descends to the selected radio minimums altitude a flashing radio minimums alert is displayed on the applicable DU.

Abbreviations and Acronyms

· ADI - attitude direction indication

· AID - aircraft installed delay

· altm - altimeter

· ant - antenna

· approx - approximately

· ARINC - Aeronautical Radio, Inc.

· BITE - built-in test equipment

· CAPT - captain

· CDS - common display system

· conn - connector

· CP - control panel

· CW - continuous wave

· DEU - display electronics unit

· DH - decision height

· DME - distance measuring equipment

· DU - display unit

· EFIS - electronic flight instrument system

· F - frequency

· FCC - flight control computer

· FDAU - flight data acquisition unit

· FM - frequency modulation

· F/O - first officer

· freq - frequency

· fwd - forward

· gnd - ground

· GPWC - ground proximity warning computer

· ILS - instrument landing system

· LCD - liquid crystal display

· LED - light emitting diode

· LRU - line replaceable unit

· maint - maintenance

· MDA - minimum descent altitude

· mins - minimums

· PFD - primary flight display

· P/N - part number

· RA - radio altimeter

· RA - radio altitude

· rec - receiver

· RF - radio frequency

· rst - reset

· R/T - receiver transmitter

· S/W - software

· sys - system

· T - time

· TCAS - traffic alert and collision avoidance system

· VCO - voltage controlled oscillator

· WXR - weather radar

· xmit - transmit

RA SYSTEM - GENERAL DESCRIPTION

General

The radio altimeter system has two receiver/transmitters (R/ Ts). Each R/T has a transmit and a receive antenna. The radio altimeter R/T makes a frequency modulated continuous wave RF signal that is sent to the ground and reflected back to the airplane. The time that it takes for the signal to travel from the transmit circuit of the R/T to the receive circuit of the R/T is changed into absolute altitude. The number one system altitude shows on the captain display and the number two system shows on the first officer display.

The altitude data and signal validity is sent on two ARINC 429 data buses.

ARINC 429 data bus 1 sends data to these components:

· Flight control computers (FCC)

· Autothrottle computer.

ARINC 429 data bus 2 sends data to these components:

· Ground proximity warning computer (GPWC)

· Traffic alert and collision avoidance system (TCAS) computer

· Flight data acquisition unit (FDAU)

· Weather Radar (WXR)

· Common display system (CDS) display electronic units (DEU).

The receiver/transmitters get discrete inputs from the proximity switch electronics unit (PSEU) used to count flight legs for fault recording.

RA SYSTEM - COMPONENT LOCATION – 1

General

The RA receiver/transmitters are on the E3 rack in the electronic equipment (EE) compartment.

The RA antennas are on the bottom of the fuselage.

Дата добавления: 2015-11-14