(g)  
An output from the flag alarm circuit is also provided to the pointer stow circuit. An alarm condition activates this circuit causing the height indicator altitude pointer to freeze in position for approximately 1 second and then to be driven up behind the pointer mask.

 (h)  
When the airplane is at an altitude of over 2500 feet or for any condition when received signal strength is inadequate for normal system operation, an input is provided to the flag alarm circuit to de-energize the warn relay. This results in immediate deactivation of all altitude trip circuits, activation of the pointer stow circuit, and illumination of the receiver-transmitter WARN indicator.

 (i)  
The receiver-transmitter lights marked WARN (yellow) and FLAG (red) are controlled directly by the warn relay and flag alarm functions, respectively. The WARN lamp will light when there is a loss of signal and both the WARN and FLAG lamps will light if a malfunction occurs in the LRRA system. The four neon lights marked SENS, XMTR, COMP, and IND are controlled by the integrity gates. Power is applied to the neon lights only when the PRESS TO MONITOR button is pressed. Pressing this button will cause one or more of the neon lamps to light identifying the area in which a fault has occured.

 B. Control
 (1)  Turn on Procedure
 (a)  
Provide electrical power (Ref 24-22-00).

 (b)  
Provide equipment cooling air (Ref 21-58-00).

 (c)  
Close the ALTM LOW R1 and ALTM LOW R2 circuit breakers on the electronic circuit breaker panel.

 (d)  
The height indicator altitude pointer should indicate between -3 and -11 feet with the warning flag out of view.

 EFFECTIVITY

 SN 301-350  CONFIG 3  01 Page 10  Apr 25/8834-33-00
 LOW RANGE RADIO ALTIMETER SYSTEM - DESCRIPTION/OPERATION
________________________________________________________
 1.  General
_______
 A.  The low range radio altimeter (LRRA) system supplies vertical position information for use by the pilots during approach and landing phases of flight operation. The LRRA system provides an accurate measurement of absolute altitude (height above terrain) from 2500 feet to touchdown. Flag alarm, dc altitude, and vertical terrain clearance (altitude trip) outputs are available for use by other systems.
 B.  On LH 001-003, IB 405, two complete systems are installed in the airplane. Each system consists of a receiver-transmitter, height indicator, decision height (DH) light and rising runway display on an attitude director indicator (ADI), transmit antenna, and receive antenna. Location of components is shown on Fig. 1.
 C.  On LH 004-099, three systems are installed in the airplane. Systems 1 and 2 consist of a receiver-transmitter, height indicator, DH light and rising runway display on an attitude director indicator, transmit antenna, and receive antenna. System 3 consists of a receiver-transmitter, LRRA-3 failure annunciator, transmit antenna, and receive antenna. Location of components is shown on Fig. 1.
 2.  Receiver-Transmitters
_____________________
 A.  The receiver-transmitters are located side by side in center equipment center E9. A test connector with protective cover, three failure annunciators, and a control to reset the failure annunciators are located on the front panel. The failure annunciators identify a failure in the receiver-transmitter, height indicator, and antenna/coaxial cables. Two locking lugs secure the unit to its mount. A handle for carrying the unit is provided on the front panel.
 3.  Antennas
________
 A.  The antennas are linearly polarized horns. Two identical antennas are used in each system, one for transmitting and one for receiving. The antennas are flush-mounted on the lower fuselage of the airplane. The transmit and receive antennas are located at body station 913 and 933, respectively. System 1 antennas are to the left of the fuselage centerline. System 2 antennas are on the fuselage centerline. On airplanes with three LRRA systems, the system 3 antennas are to the right of the fuselage centerline. Coaxial cables connect the antennas to the receiver- transmitters (Fig. 1).
 4.  Height Indicators
_________________
 A.  On LH airplanes, a height indicator (HI) is located on each pilot's flight instrument panel. The height indicator provides a visual display of airplane terrain clearance. The operating controls and indicators consist of DH control knob, DH index, test pushbutton switch, dial, altitude pointer, pointer mask, and warning flag. The circular dial is graduated from -20 to 2500 feet. The graduation is linear from -20 to 500 feet and logarithmic from 500 to 2500 feet.
 EFFECTIVITY
　
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本文鏈接地址：747飛機維護手冊AMM CHAPTER 34 - NAVIGATION 第34章導航2(68)