SD3-60 AIRCRAFT MAINTENANCE MANUAL SYSTEM - DESCRIPTION & OPERATION (POST MOD A8062)

Transcription

1 AMM GYRO COMPASS SYSTEM - DESCRIPTION & OPERATION (POST MOD A8062) 1. General A. The Gyro compass system is a dual installation which provides heading data for: - one flight director system. Refer to , pb1. - one VOR/ILS/MKR system. Refer to , pb1. - the EHSI system. Refer to , pb1. 2. Description A. One identical gyro compass system is installed for each pilot. Each installation comprises the following: 3. Operation - DGS - 65 Directional gyro and electronics unit - RCP - 65 Remote compensator unit - FDU - 70 Flux detector - HPU - 74 HSI Processor Unit. The HPU-74 unit receives heading information in digital format from the DGS-65 for EHSI display. The HPU-74 forms part of the EHSI-74 system. Refer to , pb1. The DGS-65, RCP-65 and FDU-70 are described. Refer to , pb1. Refer to Figure 1. A. No.1 and No.2 gyro compass systems are supplied with 28V dc via C/B Nos 48 and 198 on 1D and 2D distribution panels respectively. An initial run up period of five minutes is recommended before system operation. No heading information will be shown on the associated EHSI or RMI until these units themselves are provided with power and the gyro compass systems provided with 26V ac reference signals. These signals are supplied via C/B Nos 305 and 356 on distribution panels 1D and 2D respectively. Once the DGS-65 has run up to speed and all relevant circuit breakers are closed, indication of systems operation is given with the HEADING flags on the associated EHSI and RMI going out of view. Page 1 Jun 30/01

2 SD3-60 AIRCRAFT MAINTENANCE MANUAL MCS-65 GYRO COMPASS SYSTEM BLOCK DIAGRAM (Typical System) Figure 1 Page 2 Jun 30/01

3 The FDU-70 senses the horiontal component of the Earth's magnetic field and provides two signals proportional to the sine and cosine of the magnetic heading angle. These signals are generated by two coils orientated 90 degrees to each other in the horiontal plane. Each set of coils consist of sensing windings and excitation windings, the excitation windings being driven by a 400 H Triangular wave form provided by the DGS-65. The resultant proportional feedback signals generated by a change of aircraft heading are sensed by the DGS-65. These signals are converted from analog to digital format and compared with data from the directional gyro and the compensation unit, thus the corrected magnetic heading data is computed. The resultant heading data is provided in serial and parallel digital format, the serial data being made available to the HPU-74. The parallel digital heading data is converted to two independent analog outputs, X-Y-Z synchro format with Z at ground. These outputs supply: - the associated RMI. Refer to , pb1. - the FDR. Refer to , pb1. with heading information. The data passed to the HPU-74 is processed and used to supply the EHSI with display information. The aircraft heading is read from the displayed compass card (in white) against the triangular yellow lubber line. Also displayed are the letters "DG" (directional gyro) in yellow to the left of the lubber line. If a failure of the compass system occurs the lubber line will be replaced by a white box with the letters HDG in red. The letters will flash for ten seconds, then become steady, DG mode aunnunciation will also be removed. NOTE: Further information regarding EHSI display is provided. Refer to , pb1. Page 3 Jun 30/01

4 AMM GYRO COMPASS SYSTEM - MAINTENANCE PRACTICES (POST MOD A8062) 1. General Compasses should be check-calibrated as detailed in para. 2, whenever:- (1) the accuracy of the compass is suspect. (2) there is any modification, repair, or major replacement involving magnetic material. (3) a change of freight load is likely to affect the compass reading. (4) a compass has been subjected to shock, e.g. after a heavy landing. (5) the aircraft has passed through a severe electrical storm. (6) a significant change is made to the electrical or radio installation. (7) A check should always be made on each heading to ensure that neither the interference from each individual item of electrical equipment and its associated wiring, nor the interference from the most adverse combination of the possible electrical load has been increased. (8) the sphere of operation of the aircraft is changed to one of different magnetic latitude. (9) the aircraft has been in long term storage. 2. Adjustment/Test A. Bench Tests The gyro magnetic compass system is to be bench tested in accordance with the procedures in the relevant manufacturers manual. B. Pre-Installation Checks Check that the units are free from signs of mechanical damage, corrosion or other defects. C. Post-Installation Tests System Test (1) Refer to , pb301. Provide electrical power to the aircraft. (2) Apply ac and dc power to the gyro compass system and associated RMI and EHSI systems. (3) Confirm that the HEADING flags go out of view within two minutes and the system fast slaves to the correct heading. Page 201

5 SD3-60 AIRCRAFT MAINTENANCE MANUAL (4) Remove the mounting screws securing the DGS-65 to the aircraft. Turn the DGS-65 clockwise, viewed from the top. Check that the compass card rotates counterclockwise (heading increases). (5) Repeat para (4) for a counter-clockwise rotation of the gyro. (6) Replace the DGS-65 attaching screws. ow the system to slow slave and confirm the indicated headings are approximately the same as indicated by the standby compass. (7) Repeat paras (2) to (6) for the No. 2 gyro compass system. NOTE: The gyro compass system must be realigned if the following tests are performed. (8) Remove the screws securing the flux detector unit to the aircraft and turn the unit approximately 30 degrees clockwise when viewed from the top. Confirm that the heading indication increases at a rate of approximately 2.5 degrees per minute. Repeat the operation turning the unit counterclockwise. (9) Replace the screws attaching the flux detector to the aircraft. (10) Repeat para (8) and (9) for the No. 2 gyro compass system. (11) Complete compass swing as detailed in para B. D. Compass Swing NOTE: (1) When replacing identical gyro units or re-installing the same unit there is no need to perform a compass swing. (2) When replacing a gyro unit type -001 with type -002 or vice versa, there is no need to perform a compass swing. (3) In the event of a replacing or re-installing a flux detector or a compensating unit, the compass swing must be performed. (4) Compass swings must be carried out on an approved compass base. Equipment required: - a precision calibration compass, ± 0.25 degree accuracy with a sighting facility. - a digital voltmeter of 1 mv accuracy, up to ± 15 volts range. - jewellers screwdrivers. - compass graph sheet. Refer to Figure 202. NOTE: Compass swings must be performed on an approved compass base. (1) Preparation (a) Ensure that the weather is suitable (adequate light for aircraft positioning and manoeuvring, less than 15 knots windspeed). Page 202

6 (b) Ensure that all equipment, cover panels and hardware normally carried in the aircraft are in their normal positions. NOTE: Ensure all wing tip bolts are secure. (c) Remove all non-flight equipment from the aircraft. (d) Fix adhesive tape of contrasting colour to the centre of the front of the fin and on the centre line above the flight compartment, to facilitate sighting. (e) Lock the flying controls using flight compartment locks; not external locks. (f) Remove all magnetic items from the clothing of personnel involved with the compass system alignment. (g) Obtain permission from Air Traffic Control and tow the aircraft to the approved compass base. (h) Refer to , pb301. Connect power to the aircraft observing any local operating restrictions. NOTE: It is not necessary for the engines to be run during the compass swing but they may be run if preferred. (i) Refer to , pb301. Switch on power and all electrical and avionic services which are in normal operation during flight. Ensure gyro compass system and the flight guidance system have power supplied to them. NOTE: ow at least a ten minute warm up period. (j) (k) (l) On the No.1 and No.2 EHSI controller, press the HSI button on the DISPLAY selection. Ensure that the HEADING flags on the No.1 and No.2 EHSI and RMI are clear. Set the aircraft on a heading of 000 ± 2 degrees. (m) Locate No.1 and No.2 compass compensators, RCP-65, in the left hand and right hand equipment compartments and remove the front covers. (The front of the compensators must be accessible during the compass swing). (n) Press and hold the set-up mode microswitch. NOTE: The set-up mode microswitch may be held in position using a locally manufactured plastic strip approximately 0.4 inches wide, held in place with the cover screws. Ensure the strip does not impede access to the test socket or compensation controls. Page 203

7 SD3-60 AIRCRAFT MAINTENANCE MANUAL RCP-65 Compensation Control and Test Figure 201 Page 204

8 (o) Refer to Figure 201. Connect the voltmeter to the test point as follows; adjust the relevant compensation controls to obtain readings of 0 ± 5mv in each case. 1 Sine compensation signal, TP1 (+) and signal ground point TP5 (-). 2 Cosine compensation signal, TP2 (+) and TP5 (-). 3 Index compensation signal, TP6 (+) and TP5 (-). NOTE: voltages at test points are dc. (2) Perform compass swing as follows: (a) Obtain and note the actual aircraft heading by sighting the datum compass on the tape fixed to the fuselage and fin. (b) Check that the RMI readings agree with the associated EHSI readings ± 1. Note both EHSI readings. Calculate the deviation (Dev = datum compass reading - gyro compass reading). NOTE: If a tractor is used to position the aircraft during the compass swing it may be necessary to remove the tractor from the aircraft before recording any heading data. This can be confirmed by observing the EHSI heading with the tractor attached and again with the tractor removed to a distance of at least 30m (100 ft). Check that after 5 minutes the changes in compass readings do not exceed 0.5 degrees. If a greater change is noted, the tractor must be removed from the aircraft before heading data is recorded. (c) Position the aircraft at 90 ± 2 degrees, allow time for the compasses to stabilie. Note datum compass reading and the EHSI reading. Calculate the deviation. (d) Position the aircraft at 180 ± 2 degrees, allow time for the compass to stabilie. Note datum compass reading and the EHSI reading. Calculate the deviation. (e) Obtain coefficient C for each compass. C = (deviation on S - Deviation on N) 2 (f) Refer to Figure 201. Connect the voltmeter between TP1 (+) and TP5(-) and adjust the sine compensation control (center) of both units to correct for coefficient C. NOTE: (1) This adjustment is achieved by making the compass read its present figure plus the coefficient. (2) The voltmeter is used to guide adjustment, 1 volt equals approximately 2. (3) Turning the compensation control clockwise increases the voltage thus increasing the compass reading. Page 205

9 SD3-60 AIRCRAFT MAINTENANCE MANUAL (g) Position the aircraft at 270 ± 2 degrees, allow time for the compass to stabilie. Note the datum compass reading and the EHSI reading. Calculate the deviation. (h) Obtain coefficient B for each compass B = (deviation on W - Deviation on E) 2 (i) (j) Refer to Figure 201. Connect the voltmeter between TP2 (+) and TP5 (-) and adjust the cosine compensation control (right) of both units to correct for coefficient B. Refer to NOTE (1), (2) and (3). Using the readings obtained on the four cardinal points before adjustment, obtain the index error using the following formula: (Deviation Deviation Deviation Deviation 270) 4 = index deviation = coefficient A Page 206

10 Compass graph sheet - example Figure 202 Page 207

11 SD3-60 AIRCRAFT MAINTENANCE MANUAL (k) (l) Refer to Figure 201. Connect the voltmeter between TP6 (+) and TP5 (-) and adjust the index compensation control (left) of both units to correct for coefficient A. Refer to NOTE (1), (2) and (3). Remove the plastic strip or tape from the set-up mode microswitch and replace the compensation unit covers. (m) Check swing the aircraft every 90 degrees starting at 000 degrees. Make further corrections for coefficients A, B and C as necessary. Repeat until corrections give no further benefit and the four readings are accurate to 1 degree. (n) Check swing the aircraft every 45 degrees. Check that resultant final error does not exceed 2 degrees. (o) Plot final deviations on a result graph and produce deviation cards for each gyro compass. (3) Completion (a) Set AVIONICS MASTER switch to OFF, set ELECTRICAL MASTER switch to OFF. (b) Refer to , pb301. Disconnect power supply. (c) Remove adhesive tape from fin and fuselage. (d) Obtain permission from ATC and tow the aircraft back to the hangar. Page 208