A
DH LIGHT

SWITCH
RISING RUNWAY
MASK POINTER FLAG

DH CONTROL KNOB,DH INDEX
ON/OFF SWITCH AND RESET SWITCH (ON-OFF CAPABILITY
REMOVED FROM AF
TEST
FREIGHTERS
BUTTON
ATTITUDE DIRECTOR INDICATOR 155 AND ON)
B HEIGHT INDICATOR
B
Low Range Radio Altimeter System Component Location
Figure 1 (Sheet 1)

EFFECTIVITY

CONFIG 2
AF ALL; MD ALL
7XA Page 2
GN ALL; VM ALL
34-33-00
Apr 25/88

AFT CENTER EQUIPMENT CENTER

DH LIGHT
TEST
DH CONTROL KNOB
BUTTON DH INDEX
ATTITUDE DIRECTOR INDICATOR AND RESET SW
B HEIGHT INDICATOR
B
Low Range Radio Altimeter System Component Location
Figure 1 (Sheet 2)

EFFECTIVITY

CONFIG 2
SN 351-399
799 Page 3
34-33-00
Apr 25/88

AFT CENTER EQUIPMENT CENTER

POINTER ALTITUDE
MASK POINTER

RISINGDH INDEX DH INDEXSWITCHRUNWAY
CONTROL KNOB AND RESET SW
Low Range Radio Altimeter System Component Location Figure 1 (Sheet 3)
EFFECTIVITYAT ALL

CONFIG 2 799 Page 4
34-33-00
Apr 25/88

LRRA System Block Diagram
Figure 2 (Sheet 1)

EFFECTIVITY CONFIG 2 AF,MD,GN,AT,VM ALL
799 Page 5
34-33-00
Sep 25/94

LRRA System Block Diagram
Figure 2 (Sheet 2)

EFFECTIVITY CONFIG 2 SN 351-399

799 Page 6
34-33-00
 Apr 25/88
 T34472
 C.  On SN 351-399, the No. 2 system transmitting antenna is located on the lower fuselage centerline between the No. 1 and No. 3 transmitting antennas at body station 913. The No. 2 receiving antenna is located between the No. 1 and No. 3 receiving antennas at body station 933. Coaxial cables connect the antennas to the receiver-transmitters.
 4.  Height Indicators
_________________
 A.  A height indicator 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 a DH control knob, DH index, test pushbutton switch, dial, altitude pointer, pointer mask, warning flag, and off flag. The circular dial is graduated from
 XA -20 to 2500 feet. The graduation is linear from -20 to 500 feet and XA logarithmic from 500 to 2500 feet.
 B.  The warning flag appears and covers the dial in the vicinity of the 100-foot indication when a malfunction occurs in the system. The off flag appears and covers the warning flag when the system is turned off. The altitude pointer is driven underneath the pointer mask at altitudes above 2500 feet and when a malfunction occurs in the system. The DH control knob adjusts the position of the DH index (cursor) on the altitude scale thereby selecting the altitude at which the DH light operates. On some systems, the DH control knob is also the system on/off control (Ref Fig. 1).
 C.  The DH control knob is used to adjust the position of the DH cursor (index) to any altitude shown on the dial. The DH cursor setting designates the altitude at which the DH light at the associated ADT will come on during airplane descent or go off during airplane ascent.
 D.  On AF 155, 156, 158-160, 162-182, 185-199, SN 351-399, an audio warning is provided to the interphone system at altitudes from approximately 50 feet above DH down to DH.
 5.  ADI Displays
____________
 A.  A DH light is located on each pilot's ADI. The operation of the DH light is controlled by the height indicator located on the same instrument panel. The DH light has a press-to-test feature to check for DH light burnout.
 B.  The rising runway symbol displays both radio altitude and localizer deviation. Radio altitude is presented by the distance between the top edge of the runway symbol and the base of the fixed airplane symbol. Localizer deviation is presented by the runway symbol moving left or right across a horizontal scale (Ref 34-31-00).
 6.  Operation
_________
 A.  Functional Description
 (1)  Altitude measurement operation (Fig. 3)
 (a)  The LRRA system provides altitude data when 115-volt ac power is supplied to the receiver-transmitter from the applicable ALTM LOW circuit breaker at the P7 overhead panel. Low voltage power is then supplied to all circuits in the receiver-transmitter and to the height indicator power supply. On some systems, the system is turned on by rotating its DH control knob clockwise in addition to closing the primary power circuit breakers at the P7 panel (Ref Fig. 1).
 EFFECTIVITY
 AF ALL; SN351-399; MD ALL;  CONFIG GN ALL; AT ALL; VM ALL  ATG Page 7  Sep 25/94

34-33-00