AMM 17.0.0.0GYRO COMPASS SYSTEM - DESCRIPTION & OPERATION (PRE-MOD A8062) 1. Description A. General Two Collins MCS-65 Gyro Magnetic Compass systems are installed in the aircraft, one for each pilot. Each system provides heading data, with respect to magnetic north for: - one Flight Director system. Refer to 34-23-00, pb1. - one VOR/ILS/Marker Beacon system. Refer to 34-31-00, pb1. Each installation is comprised of the following three units:- - DGS-65 - Directional gyro and electronics unit. - RCP-65 - Remote compensator unit. - FDU-70 - Flux detector. B. Detail (1) Directional gyro and electronics unit. (Part number 622-6136-001). The DGS-65 consists of two distinct parts, the directional gyro and the compass electronics. The gyro is air erected and has an optical incremental pick off which has an angular resolution of 0.125 degrees. This incremental angle data is used in conjunction with the sine and cosine inputs from the flux detector to generate a heading value. The gyro is microprocessor controlled and the heading data thus generated is transmitted both in digital form and standard ARINC. synchro form. There are three outputs; one digital and two synchro. The digital output is used when an autopilot is fitted for calculating such things as yaw rate. The two synchro outputs are used to drive the associated Flight Director system horiontal situation indicator (HSI-70) and VOR/ILS/Marker Beacon system radio magnetic indicator (RMI-36), both located on panel 1P. The 1st and 2nd pilots DGS-65, idented 1FC2 and 2FC2, are respectively located in numbers 3 and 4 radio bays. A more detailed description is provided in the relevant Collins publication. (2) Remote compensator unit (Part Number 622-6174-001). The RCP-65 is used primarily for swinging the compass system. It incorporates six test points and three potentiometers. The units, No.1 and No.2, and idented 1FC3 and 2FC3 are respectively located left and right at frame station 68 below pilots floor. A more detailed description is provided in the relevant Collins publication. Page 1 Jun 30/01
SD3-60 AIRCRAFT MAINTENANCE MANUAL 2. Operation (3) Flux detector (Part number 622-5812-001) The FDU-70 consists of two sets of coils, orientated at 90 degrees to one another, known as the sine and cosine coils. These are designed to sense the horiontal component of the earths magnetic field. The units are aligned with the aircraft horiontal axis (± 1.0 degrees), with the mounting surface perpendicular to the yaw axis (± 5.0 degrees). The units, No.1 and No.2, and idented 1FC4 and 2FC4 are respectively located in the left and right wing tips. Refer to Figure 1. The No.1 and No.2 Gyro Compass systems are respectively supplied with a 28V D.C. operating power via C/B Nos. 48 and 198 on 1D and 2D distribution panels. An initial warm-up period of five minutes is required. No heading information will be shown on the associated HSI-70 and RMI 36 until these units are themselves provided with power, and the Gyro Compass systems are provided with 26 V. A.C. reference signals. The required signals are respectively supplied to the No.1 and No.2 systems via C/B Nos. 305 and 356 on 1D and 2D distribution panels. The 28V D.C. operating power is respectively supplied to the No.1 HSI-70 and the No.1 RMI-36 via C/B Nos. 57 and 404 on 1D and 5D distribution panels. The 26V A.C. reference signals are supplied via C/B Nos. 305 and 356 on distribution panels 1D and 2D to the No.1 HSI-70 and the No.1 RMI-36 respectively. The 28V D.C. operating power is respectively supplied to the No.2 HSI-70 and the No.2 RMI-36 via C/B Nos. 179 and 434 on 2D and 6D distribution panels. The 26V A.C. reference signals are supplied via C/B Nos. 305 and 356 on distribution panels 1D and 2D to the No.2 RMI-36 and the No.2 HSI-70 respectively. Once the gyro in the DGS-65 has run up to speed and all relevant circuit breakers are closed, indication that the system is operable is given by the HEADING flags on the associated HSI-70 and RMI-36 units going out of view. The DGS-65 provides two 400 H triangular waveform signals to excite the FDU-70 sine and cosine coils. These coils then sense the horiontal component of the earths magnetic field and send the sine and cosine components of this back to the DGS-65. The signals are then amplified and directed to the DGS-65 microcomputer and to the RCP-65. The voltage level of the sine and cosine signals can be measured at the RCP-65 when swinging the compass system to calculate the compensation voltages which are then set up on the three potentiometers in the RCP-65. These compensation voltages are used by the DGS-65 microcomputer to bias the sensed sine and cosine voltages from the FDU-70. The resultant is then put into synchro format and outputed to the HSI-70 and RMI-36. The system normally fast slows on start-up to the correct heading and then goes into a slow slave mode of operation, the slow slave speed being 2.5 degrees/minute. Faster movement of the displays is obtained from the gyro input to the DGS-65 microcomputer which allows each display to follow the aircraft in any yawing manoeuvre. Page 2 Jun 30/01
MCS-65 System Block Diagram (Typical System) Figure 1 Page 3 Jun 30/01
AMM 18.0.0.0GYRO COMPASS SYSTEM - MAINTENANCE PRACTICES (PRE 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 Compass System should be tested in accordance with the procedure in the relevant manufacturers manual (Collins). B. Pre-installation tests Check that the units are free from signs of mechanical damage, corrosion or other defects. C. Post-installation tests (1) Ensure that the following units are operational and that the appropriate circuit breakers are made: - Horiontal Situation Indicators. Refer to 34-23-10, pb1. - Radio Magnetic Indicators. Refer to 34-31-10, pb1. (2) Ensure that all electrical and avionic switches are in the neutral or OFF position. (3) Refer to 12-09-03, pb301.connect an external power supply to the aircraft. Page 201
SD3-60 AIRCRAFT MAINTENANCE MANUAL (4) Select ELECTRICAL MASTER switch to EXTERNAL POWER. (5) Ensure C/B Nos. 48 and 198, on panels 1D and 2D respectively, are closed. (6) Select AVIONICS MASTER switch to ON and check: (a) HDG flags on RMIs and HSIs are out of view within one minute. (b) RMIs and HSIs fast slave until synchronised (indicated by cards going to north and then rotating quickly to sensed heading). (7) Gain access to the No.1 DGS-65 and remove the four mounting bolts. Turn the DGS-65 clockwise, viewed from the top, and check that the heading on No.1 HSI and No.2 RMI moves towards increasing numbers, following the DGS-65 movement. (8) Repeat para (7) for a counterclockwise movement of the DGS-65. (9) Replace the DGS-65 mounting bolts. ow the system to slow slave and confirm that the indicated headings are approximately the same as indicated by the standby compass. Refer to 34-22-00, pb1. (10) Repeat para (7) to (9) for the No.2 DGS-65 checking the heading on No.2 HSI and No.1 RMI. (11) Refit access panels. NOTE: The compass swing must be carried out if the following tests are performed. (12) Gain access to No.1 FDU-70 and remove the three securing screws. Turn the FDU-70 approximately 30 clockwise when viewed from the top and confirm that the heading indication on No.1 HSI and No.2 RMI increases at a rate of approximately 2.5 per minute. Repeat the operation turning the No.1 FDU-70 counterclockwise. (13) Secure the No.1 FDU-70 to its mounting with the three non-magnetic screws and washers. (14) Repeat paras (12) and (13) for the No.2 FDU-70 checking the heading on the No.2 HSI and No.1 RMI. (15) Refit access panels. 3. 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. Page 202
(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. A. Equipment and Materials required (1) A precision calibration compass, accuracy ± 0.25. (2) Adhesive tape of two contrasting colours, width 1 inch. (3) Deviation cards. (4) Compass graph sheets. (5) Digital voltmeter which reads ±15 volts and accuracy of 1mV, and one second response time. (6) Short, non-magnetic screwdriver for compass correction adjustments. B. Conventional compass swing. (1) Ensure that the light is adequate and wind speed is below 15 knots. (2) Fix adhesive tape of contrasting colour to the centre of the front of the fin and on the centre line above flight compartment to facilitate sighting. Accuracy +0.25 inch. ENSURE ALL WING TIP BOLTS ARE SECURE (3) Remove all equipment not carried in flight from the aircraft and ensure that all equipment normally carried is in its correct position. (4) Lock the flying controls using the flight compartment lock level - not external locks. (5) Obtain permission from Air Traffic Control and tow the aircraft to the compass base. (6) Set aircraft on heading 000 ±2 with tractor attached. (7) Switch on power and all electrical services which could cause compass errors in cruising flight, observing any ground operation restrictions. ALLOW TEN MINUTE WARM UP. (8) Check that heading flags on HSI's and RMI's are clear and that slaving indicators eventually oscillate about the centre mark. (9) Remove covers from compass compensators. Hold the internal microswitch buttons pressed. This may be effected with plastic strips approximately 0.4" wide held in place with two of the cover screws. The strips must not impede access to the test socket or compensation controls. Page 203
SD3-60 AIRCRAFT MAINTENANCE MANUAL (10) Connect the voltmeter to the socket holes as follows and adjust relevant compensation controls for a reading of 0 ±5 mv in each case:- (a) Hole 5 (-); Hole 6 (+); Index compensation control (trimmer nearest case). (b) Hole 5 (-); Hole 1 (+): Sin compensation control (centre trimmer). (c) Hole 5 (-); Hole 2 (+): Cosine compensation control (trimmer nearest socket). NOTE: 1. By keeping a record of correction voltages of fully adjusted compasses it should be possible to set in approximately correct values at this stage. 2. A diagram showing the compass compensator layout is given. Refer to, Figure 1. (11) Obtain and note the actual aircraft heading by sighting the datum compass on the tape fixed to fuselage and fin. (12) Check that the RMI card readings conform ±1 to associated HSI readings. Note both HSI readings. (13) Remove the tractor at least 50 yards from the aircraft. Check that (after 5 minutes) the changes in compass readings do not exceed 0.5. Re-attach the tractor to the aircraft. (14) Position the aircraft at 90 ± 2. ow time for the compasses to stabilise. Note datum compass reading and both HSI readings. (15) Position the aircraft at 180 ± 2. ow time for the compasses to stabilise. Note datum compass reading and both HSI readings. (16) Obtain coefficients C for each compass. = (Deviation on N - Deviation on S) 2 (17) Connect the voltmeter to holes 1 and 5 of each corrector in turn. Adjust the sin compensation control (centre) in each to correct for coefficient C. This is effected by making the compass read its present figure minus coeffieient C. NOTE: The voltmeter is used to guide adjustment where 1 volt approximately equals 1.5 degrees change in compass heading. After adjustment allow each compass to stabilise. (18) Position the aircraft at 270 ± 2. ow time for the compasses to stabilise. Note datum compass reading and both HSI readings. (19) Obtain coefficient B for each compass. = (Deviation on E - Deviation on W) 2 Page 204
(20) Connect the voltmeter to holes 2 and 5 of each corrector in turn. Adjust the cosine compensation control (nearest socket) in each to correct for co-effiecient B. This is effected by making the compass read its present figure minus coefficient B. NOTE: 1 Volt approximately equals 1.5 degress change in compass reading. (21) Using readings obtained on the four cardinal points before adjustment, obtain the index error for each compass from the formula:- (Deviation 000 + Deviation 090 + Deviation 180 + Deviation 270) 4 = Index deviation = Coeffecient A (22) Connect the voltmeter to holes 5 (negative) and 6 of each corrector in turn. Adjust the index compensation control (nearest case) to correct for coefficient A. NOTE: 1 volt approximately equals 2 degress change in compass reading. (23) Replace the compensator lids and check swing the gyro compasses every 90 starting at 0. (24) Make further corrections for coefficients A,B, & C as necessary. Repeat until no further corrections give any benefit and the four readings are accurate to 1. (25) Check swing the compass every 45. Check that no resulting final error exceeds 2. (26) Plot final deviations on a results graph and produce deviation cards for each gyro compass. Page 205
SD3-60 AIRCRAFT MAINTENANCE MANUAL Test Socket and Compensation Control Layout Figure 1 Page 206
C. Electrical compass swing (1) Ensure that the light is adequate and wind speed is below 15 knots. (2) Fix adhesive tape of contrasting colour to the centre of the front of the fin and on the centre line above flight compartment to facilitate sighting. Accuracy + 0.25 inch. ENSURE ALL WING TIP BOLTS ARE SECURE (3) Remove all equipment not carried in flight from the aircraft and ensure that all equipment normally carried is in its correct position. (4) Lock the aircraft flying controls using the flight compartment lock lever - not external locks. (5) Obtain permission from Air Traffic Control and tow the aircraft to the compass base. (6) Set aircraft on heading 000 ± 2 with tractor attached. (7) Switch on power and all electrical services which could cause compass errors in cruising. ALLOW TEN MINUTE WARM UP. (8) Check that heading flags on HSI's and RMI's are clear and that slaving indicators eventually oscillate about the centre mark. (9) Obtain and note the actual aircraft heading by sighting the datum compass on the tape fixed to fuselage and fin. (10) Check that the RMI card readings conform ± 1 to associated HSI readings. Note both readings. (11) Remove the tractor at least 30 yards from the aircraft. Check that (after 5 minutes) the changes in compass readings do not exceed 0.5. Re-attach the tractor to the aircraft. (12) Position the aircraft at 90 ± 2. ow time for the compasses to stabilise Note datum compass reading and both HSI readings to an accuracy of 0.5. (13) Position the aircraft at 180 ± 2. ow time for the compasses to stabilise. Note datum compass reading and both HSI readings. (14) Position the aircraft at 270 ± 2. ow time for the compasses to stabilise. Note datum compass reading and both HSI readings. (15) Remove covers from compass compensators. Page 207
SD3-60 AIRCRAFT MAINTENANCE MANUAL (16) Connect the voltmeter to the socket holes as follows and record the voltage read. Refer to, Figure 1. (a) Hole 5 (-); hole 1 (+): Sin compensation voltage. (b) Hole 5 (-); hole 2 (+): Cosine compensation voltage (c) Hole 5 (-); hole 6 (+): Index compensation voltage. (17) Repeat the calculations as laid out in procedures (18) to (26) for each compass system swing. (18) Calculate the error on each cardinal heading. (19) Add the four errors calculated in procedure (17) together and divide by 4. (This average error is the index error in degrees). (20) Multiply the value obtained in procedure (18) by 0.53. (This is the index error in volts). (21) Subtract the value obtained in procedure (18) from each of the four errors calculated in paragarph (17). (This removes the index error from the calculation). NOTE: The four values obtained in procedure (20) will be labelled as follows:- E N = Resultant north error E E = Resultant east error E S = Resultant south error E W = Resultant west error (22) Using the following equations calculate four more values:- (a) Sin bias N = (1.65 x E N ) 57.3 (b) Sin bias S = (1.65 x (-E S )) 57.3 (c) Cosine bias E = (1.65 x (-E E )) 57.3 (d) Cosine bias W = (1.65 x E W ) 57.3 (23) Using the values obtained in procedure (21) calculated the following values:- (a) Sin error = 11 (Sin bias N + Sin bias S ) (b) Cosine error = 11 (Cosine bias E + Cosine bias W ) (24) Add the two values obtained in procedures (16a) and (22a). (25) Add the two values obtained in procedures (16b) and (22b). (26) Add the two values obtained in procedure (16c) and (19). Page 208
(27) Connect the voltmeter to the compass compensator socket holes and adjust the voltage as follows:- (a) Hole 5 (-); hole 1 (+). Adjust sin compensation control to the value obtained in procedure (24). (b) Hole 5 (-); hole 2 (+). Adjust cosine compensation control to the value obtained in procedure (25). (c) Hole 5 (-); hole 6 (+). Adjust index compensation control to the value obtained in procedure (26). (28) Replace the compensator lids. (29) Check swing the compasses every 45. Check that no resulting final error exceeds 2. (30) Plot final deviations on a results graph and produce deviation cards for each gyro compass. Page 209