SD3-60 AIRCRAFT MAINTENANCE MANUAL - DESCRIPTION & OPERATION (PRE-MOD A8062) (1) Transceiver, Collins type DME40, (Part No.

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1 AMM DME SYSTEM - DESCRIPTION & OPERATION (PRE-MOD A8062) 1. Description A. General Two identical D.M.E. systems are installed, one for each pilot. Frequency selection is made via each respective NAV controller. Refer to , pb1. Each system comprises an indicator, transceiver and antenna. The installed systems measure the slant range distance from the operating aircraft to a selected ground station and displays this measurement, as selected, as a continuous readout in nautical miles. Each system is additionally capable of displaying the aircraft ground speed in knots or another reading of time-to-station, in minutes. The latter two readings are only accurate if the aircraft is flying straight to the selected ground station at such a distance that the slant range and ground range are nearly equal. An audio output for station identification is also provided. Both systems incorporate a 'hold' facility which enables the selected system to remember its last operating frequency, selected on the associated NAV controller, if that selected VOR frequency is changed, thus allowing separate control of the D M E and NAV receivers with a common control unit. This selection is accomplished using a NORM/HOLD switch on the relevant D M E indicator. Indication of 'hold' selection is provided in the middle aperture of the three on the indicator facia. B. Detail (1) Transceiver, Collins type DME40, (Part No ) The No.1 and No.2 transceivers, idented RB3 and 2RB3, are respectively mounted in the No.1 and No.2 radio bays. Refer to , pb1. Each transceiver is tuned by its associated NAV controller using two-out-of-five frequency information to select the required transmit and receive frequencies. The DME frequency is automatically selected for the DME when the associated NAV controller is tuned to the required VOR or ILS localier frequency. Refer to , pb1. An audio output is provided from the receiver, the level of which is controlled by a DME VOL control knob adjacent to the relevant DME indicator on panel 1P. (2) DME Indicator, Collins type 339F-12B, (Part No ) The indicators, No.1 and No. 2, are mounted at their associated pilots positions and are idented 'JK' and 'JM' respectively. The units display distance information in two apertures on the presented facia. The upper aperture will display continuously updated distance to the selected ground station, in nautical miles. The lower aperture displays either the Page 1

2 SD3-60 AIRCRAFT MAINTENANCE MANUAL 2. Operation aircraft ground speed or the time in minutes, required for the aircraft to arrive at the selected ground station; both these readings are continuously updated. NOTE: These latter two readings are only accurate when the slant range of the aircraft to the selected station is almost equal to the ground distance and the aircraft is flying directly towards the ground station. Selection of the display in the lower aperture is controlled by an OFF/MIN/KTS knob to the lower right of the indicator. This switch is the power control for the system. A further knob - DIM - controls the lighting intensity of the indicator. Selection of the 'hold' mode is achieved by selecting the NORM/HOLD knob, on the lower left of the indicator to HOLD. Indication of the 'hold' condition is given in the middle aperture. A TEST button is located on the upper right of the indicator, and when pressed initiates a system self test. A more detailed description of the indicator is provided in the relevant Collins manual. (3) Antenna, Dorne & Margolin type DMNI 70-1 The No.1 and No.2 system antennae, idented RB8 and 2RB8, are respectively located on the underside of the aircraft at Stns and V DC operating power is supplied to the No.1 and No.2 DME systems via C/B Nos. 406 and 436 on distribution panels 5D and 6D respectively. As the DME frequency is selected using the relevant NAV controller it is necessary for the VOR/ ILS/Marker beacon system to be active before correct DME system operation can be obtained. Either DME system is operational with the OFF/MIN/KTS switch on the relevant indicator selected to MIN or KTS and the appropriate NAV controller function switch selected to NAV or DME. Refer to , pb1. The required DME frequency is selected on the NAV controller by selecting the appropriate VOR or ILS localier frequency. The DME system will commence searching until it locks onto a DME reference paired with the tuned NAV frequency. Failure of the DME to lock onto the station is indicative that the selected station may be beyond the reception range of the system. In operation the selected DME transmits pulse pairs from the relevant antenna by line-of-sight to the selected ground station. The ground station, on receiving the interrogation, delays then transmits back a reply pulse pair for most interrogations. This reply frequency is offset from the aircraft frequency by 63 MH, and the time elapsed between the aircraft transmission and the reply is used by the DME system to compute the distance to the ground station. This computed information is finally displayed on the indicator in nautical miles. Page 2

3 With the system locked onto a station, the upper window of the indicator will display continuously updated slant range from the aircraft to the selected ground station. NOTE: The difference between the slant range and the ground distance to the station may be regarded as insignificant if the aircraft is one nautical mile away from the station for every 1,000 feet altitude. With the mode switch selected KTS or MIN, relevant indication of ground speed (knots) or timeto-station (minutes) is provided. Upon approach to an airfield, it may be preferable to select another VOR frequency on the controlling NAV system, to that paired with the DME. This may be achieved by selecting HOLD, on the NORM/HOLD switch on the DME indicator thus enabling the DME to memorise the DME frequency whilst the NAV controller is changed. CAUTION: WITH THE DME IN 'HOLD' MODE, LISTEN TO THE CODED DME AUDIO IDENTIFICATION AND CONFIRM THAT IT CORRESPONDS TO THE REQUIRED BEACON. Verification of the DME frequency can be obtained directly or indirectly; directly by selecting FREQ on the NAV controller function switch which will bring up the DME frequency in the top display of the NAV controller, and indirectly by listening to the DME audio output for the DME station identification code. When the DME indicator NORM/HOLD switch is at NORM the DME frequency can be changed by the NAV controller. To remind the pilot that this is the case when he changes the NAV frequency, the TUNE button on the NAV controller is lit. When HOLD is selected on the DME indicator NORM/HOLD switch this light goes out indicating that the DME system is no longer tied to the NAV controller. 3. Self Test Self-test is initiated by pressing the DME indicator TEST button. This produces a display of 0.0 nmi and 88.8 in the knots/minute display. On release of the TEST button the indicator shows all 8's for the duration of the system memory time, which is 8 to 12 seconds. Page 3

4 AMM DME SYSTEM - MAINTENANCE PRACTICES PRE-MOD A Adjustment/Test A. Bench tests The DME system should be tested in accordance with the procedure in the relevant manufacturers Maintenance Manual. NOTE: An exception to this is the DME audio output, the setting for which is defined in the audio system test procedures. Refer to , pb201. B. Pre-installation tests Check that the units are free from signs of mechanical damage, corrosion or other defects. C. Post-installation tests (1) Function test Test equipment required:- Instrument Flight Research Corporation test set ATC600A or equivalent. (a) Refer to , pb301. Provide electrical power. (b) Switch systems on and allow for warm up. Check that any DME panel lighting provided functions correctly. (c) Operate each self-test facility by holding the indicator TEST pushbutton and check that 0.0 is shown in the top display and 88.8 is shown in the bottom display. (d) Release pushbutton and check that the display reads all 8's for 8-12 seconds, after which normal DME operation is resumed. (e) On each system check the lower window displays dashes when the system is not tuned to a D.M.E. beacon. Page 201

5 SD3-60 AIRCRAFT MAINTENANCE MANUAL (f) Check the No.1 system with a flight line test set throughout its distance and frequency ranges (all channels) to the following accuracy limits:- Distance : ± 0.2 nautical mile or ± 0.4% whichever is the greater. Ground Speed : ± 2 knots or ± 2%, whichever is the greater. Time to station : ± 1 minute or ± 4%, whichever is the greater. NOTE: The above accuracy checks must be carried out at least 3 minutes after the system has 'locked on' to the signal. This permits the system to compute the rate of change of distance to the station. (g) Set the frequency on the NAV 1 controller 0.1 MH lower than test set frequency. Check that the dashes do not appear for 8 to 12 seconds. Do not use frequencies in the 112 MH band for this test. (h) On the NAV 1 controller select the frequency for a local DME station or a test set with audio output and check that satisfactory audio signals are obtained in the following units and that the DME volume control operates satisfactorily:- 1 1st Pilot's headset 2 1st Pilot's loudspeaker 3 2nd Pilot's headset 4 2nd Pilot's loudspeaker (i) (j) (k) (l) Operate NORM/HOLD switch on the DME indicator and check that annunciator on the DME indicator is lit when HOLD is selected and that the TUNE button on the NAV 1 controller lights when NORM is selected. Select NORM on the DME indicator and obtain DME operation using a test set. Change frequency on NAV 1 controller and confirm that DME range is lost. Return NAV 1 controller to test set frequency and confirm DME range reestablished. (m) Select HOLD on the DME indicator and check that DME range is maintained when NAV 1 controller is operated to different frequencies. (n) Repeat procedures (e) to (m) for the No.2 DME and NAV2 controller. Page 202

6 (2) DME VSWR tests Test equipment required:- Approved VSWR test equipment and instruction manual. (a) Obtain access to the No.1 DME antenna, idented RB8, and disconnect the antenna feeder from the antenna. (b) Connect the test equipment to the antenna. (c) Using the relevant procedure laid down in the test equipment instruction manual, check that the VSWR does not exceed 1.5 for the following frequencies: MH MH MH (d) Disconnect the test equipment and reconnect the antenna feeder to the antenna. (e) Disconnect the antenna feeder from the No.1 DME transceiver, idented RB3 and located in the No.1 radio bay, and connect it to the test equipment. (f) Ensure that the VSWR for the antenna feeder with the antenna connected does not exceed 1.4 for the frequencies in (c) (g) Disconnect the antenna feeder from the test equipment and reconnect it to the DME transceiver. (h) Repeat procedures (a) to (g) for the No.2 DME system, reading:- No.2 DME antenna, idented 2RB8, and No.2 DME transceiver, idented 2RB3 and located in the No.2 radio bay. Page 203