GARMIN ANNUNCIATION CONTROL UNIT MD41-444
(for simulator purposes only)
Postponed (LT) my plans to build this CU
picture of real MD41-444
The MD41-( ) is a self -contained GPS Annunciation and Control unit. It combines all the necessary functions required for switching HSI/CDI data inputs between a conventional VOR receiver and the Garmin GPS approach-certified GPS receivers. In addition, the MD41-( ) contains several GPS status annunciations used to indicate modes selected by the front panel switches and various inputs from the GPS receiver.
A special ILS override feature has been incorporated to cause the MD41-( ) to automatically switch to the NAV mode when the VOR receiver is tuned to an ILS frequency. Other features include dual, 16,000 hour lamps used for all annunciations, internally lighted selection switches, automatic photocell dimming, and built-in annunciation self test. A external annunciation dimming adjustment is provided for balancing low level light conditions.
1. NAV or GPS
2. HOLD or AUTO
3. MSG and/or WPT
may be flashing depending on the status of the GPS receiver.
Press the lamp test
button, all annunciations should light. Continue pressing the lamp test button
and cover the photocell window located on the left side of the front panel. All
annunciations should dim. Annunciation brightness at the minimum dimming level
may be adjusted by rotation of the dimmer control located on the right side of
the MD41-( ) case. CW rotation lowers the dimming level.
Select NAV using the
NAV/GPS button. The presentation on the HSI/CDI will now be information from the
VOR receiver. Using a VOR test generator or equivalent VOR signal, verify that
the presentation and operation of the HSI/CDI is correct. This will include
course resolver, left-right meter, to-from meter and NAV warn flag. Now select
GPS on the MD41-( ) and tune the VOR receiver to an ILS frequency. The MD41-( )
will be forced to NAV mode and ILS information will be displayed on the HSI/CDI.
NOTE, this feature will not work if “ILS
Energize” (J1 pin 14) was not connected at the time of installation. Next,
verify that HOLD and AUTO annunciations will cycle alternately when pressing the
GPS/SEQ button two times. Press the GPS/APR button and the ARM annunciation will
illuminate. ARM can be cancelled by pressing the GPS/APR button a second time, or
by ACTV input from the GPS receiver. GPS/APR test will not work without a valid
GPS signal. Please refer to Section 4 of the Garmin GPS 155XL, GNC 300 and GNC
300XL installation manual for the remaining system tests. No periodic
maintenance or calibration is necessary for continued airworthiness of the
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