SD3-60 AIRCRAFT MAINTENANCE MANUAL

Transcription

1 AMM RADAR ALTIMETER SYSTEM - DESCRIPTION & OPERATION 1. Description A. General Refer to Figure 1. The Honeywell radar altimeter system is installed to indicate heights between 0 and 2500 ft above terrain and to send an ARINC coded altitude signal and a decision height warning to: - the ground proximity warning system. Refer to , pb1. - both flight director systems. Refer to , pb1. B. Detail 2. Operation (1) Receiver/Transmitter, Honeywell (Part number HG7502AC02). The receiver/transmitter is mounted under the floor between Stns. 351 and 376 (pre Mod 8216), or behind the rear wall of the locker at Row 9(A) between Stns. 351 and 376 (post Mod 8216), and is idented SD2. The unit generates rf pulses and measures the time taken for these pulses to travel from the transmitting antenna to the terrain and back to the receiving antenna. It then produces a signal proportional to this time. (2) Indicator, Honeywell (Part number JG1072AC09) The indicator is mounted on 1P panel and is idented 'GM'. The indicator reads 0 to 2500 ft. and has a control knob on the indicator face which serves as a PUSH TO TEST button. The control knob also sets the decision height warning index, which is a white marker, to any desired altitude up to 2500 ft. On loss of track through failure or altitude more than 2500 ft. above terrain, the altitude pointer disappears behind a NO TRACK mask. The instrument also has a power failure flag. Integral lighting is controlled by a GENERAL dimmer control on panel 1P. Refer to , pb1. (3) Antenna, Honeywell (Part number LG81-L1) The antennae are flush mounted on the underside of the aircraft at Stn 364 and are idented 1SD5 and 2SD5. The transmit antenna is 3" to the right of the aircraft centre line, mounted with its connector on the aft side, facing outboard. The receive antenna is 33" to the left of the aircraft centre line, mounted with its connector on the aft side, facing inboard. Power is supplied to the radar altimeter via C/B No. 409 on distribution panel 5D. The system provides a measurement of aircraft height above terrain, based on the interval required for a radar pulse to travel from the transmitter antenna to the terrain, and back to the receiving antenna. Page 1 Apr 03/15

2 SD3-60 AIRCRAFT MAINTENANCE MANUAL For heights up to 2500 ft. the system transmits 7000 pulses per second for constant update of the height information. This information also updates a memory which serves as the height output for periods of up to 0.2 seconds during signal fades. After this period or if the aircraft is above 2500 ft for longer than 1.2 seconds the indicator pointer goes behind the NO TRACK mask. The system continues to send out the radar pulses in search of a target and while there is no return the system self tests every five seconds. While in this automatic self test mode the pointer is inhibited from moving to the self test height as in the manual self test mode. The radar altimeter system is also connected to the ground proximity warning system and both flight director systems. The radar altimeter provides a failure warning output which, when the radar altimeter fails, brings the RAD ALT flags on the flight director ADI's into view and makes the ground proximity warning system inoperative, lighting the GPWS INOP warning indicator. The radar altimeter also provides an encoded height output in standard ARINC format which is used to drive a pointer against a ero to 200 ft. scale on each flight director ADI and as a relative height input to the ground proximity warning system. A third output from the radar altimeter is the decision height output. When the aircraft descends through the height set by the decision height warning index, the DH light on the flight director ADI lights and the ground proximity warning system gives out the aural warning 'MINIMUMS - MINIMUMS' once. The fourth output is a self test inhibit which prevents the ground proximity warning system from reacting to the 1000 ft. test height during a radar altimeter self test. 3. Self Test When the PUSH TO TEST knob is depressed, a simulated 1000 ft. height is introduced into the system. Satisfactory operation is indicated by the correct altitude of 1000 ± 100 ft. appearing on the indicator Page 2

3 Radar Altimeter System - Location Figure 1 Page 3

4 AMM RADAR ALTIMETER SYSTEM - MAINTENANCE PRACTICES 1. Adjustment/Test A. Bench tests The radar altimeter system should be tested in accordance with the procedure in the relevant manufacturers Maintenance Manual. B. Pre-installation tests Check that the units are free from signs of mechanical damage, corrosion, or other defects. C. Post-installation tests CAUTION: THE AIRCRAFT MUST NOT BE INSIDE A METAL HANGAR AS THE ENERGY RADIATED BY THE SYSTEM CAN CAUSE MULTIPATH REFLECTION SIGNALS WHICH COULD CAUSE ERRONEOUS OR ERRATIC SIGNALS. (1) With power off, check that the indicator power flag and the RAD ALT flag on each flight director ADI are in view. (2) Apply electrical power. Refer to , pb301. (3) After approximately 30 seconds check that:- (a) The indicator power flag is clear. (b) The RAD ALT flag on each flight director ADI is clear. The indicator pointer is approximately ero. NOTE: 1. The indicator pointer may fluctuate momentarily between the NO TRACK and OFF positions during warm-up. 2. If, after flag clear, the indicator does not read exactly ero adjust the transceiver as follows:- (i) Rotate the adjustment hole cover at the lower rear of the unit. (ii) With a suitable screwdriver rotate the ero adjustment until the indicator reads ero. (iii) Replace the cover. (4) Set the decision height warning index on the indicator at 200 ft. by rotating the control knob. (5) Check that the indicator still reads ero and that the DH lights on the flight director ADI's are illuminated. Page 201

5 SD3-60 AIRCRAFT MAINTENANCE MANUAL (6) Press and hold the PUSH TO TEST knob on the indicator and check that:- (a) The indicator reads 1000 ± 100 ft. (b) Both flight director ADI indicators are past full scale. Both flight director ADI DH lights are out. (7) Release the PUSH TO TEST knob and check that:- (a) The indicator pointer returns quickly and smoothly to ero. (b) Both flight director ADI indicators are at ero. Both flight director ADI DH lights are illuminated. Page 202