Baron 58 Cockpit Simulator

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(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.



Alternate action switch, when pressed, will select VOR or GPS presentation on HSI/CDI.


Momentary switch, when pressed, will control GPS Approach Mode.


Alternate action switch, when pressed, will select between AUTO and HOLD modes.


Momentary switch for testing annunciation lamps.



VOR information presented on the HSI or CDI.


GPS information presented on the HSI or CDI.


GPS is armed for automatic transition to approach mode.


GPS is actively engaged in the approach mode.


This will activate the course selector and also disable the automatic GPS waypoint sequencing.


This will disable the course selector input to the GPS and will enable automatic GPS waypoint sequencing.


GPS message alert, from GPS receiver.


GPS waypoint alert, from GPS receiver



 Turn on the avionics master switch and the MD41-( ) should come on with the following annunciations.

1. NAV or GPS


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 MD41-( ).




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