05/04/16
Overview
The navigation display unit (NDU) system is an integrated navigation computer and display system. It receives navigation data from the inertial reference system (IRS) and from pilot inputs. It gives the position data in relation to waypoints manually set by the pilot. The NDU system shows the navigation data on its alphanumeric displays. The electronic flight-instrument system (EFIS) can also show this data.
The NDU system consists of one Lasertrak navigation display unit. The NDU is a combined navigation and display unit, which interfaces with all three IRUs and three IACs.
The Lasertrak NDU is a backup navigation system with a dual FMS installation. It provides an alternate means of initializing the three IRUs, and a digital display of navigation data from any one of the IRUs.
Note:
When a third FMS is installed, the NDU is removed. The third FMS becomes the third reference system for long-range navigation.
The Lasertrak NDU’s navigation capability handles up to nine waypoints and the systems output can be displayed on EFIS.
The NDU system is not installed in aircraft with three flight management systems. The NDU indicates a failure via a CAS message.
05/04/16
Navigation Display Unit
The NDU is located on the left side panel and contains the following:
- Data entry keyboard
- Special function keyboard
- System select keyboard
- Data select keyboard
- Display
- Fault annunciator
- ON/OFF switch
The NDU weighs 3.8 lbs (1.72 kg) and operates with a +28 VDC power supply. It is installed in the pilot’s side console in the flight compartment. Four fasteners hold the NDU in its position. The NDU has three connectors that connect to the IRUs, IACs, and other avionics systems.
The NDU uses the IRS and pilot input data to supply basic navigation functions. It has an integrated control/display panel that permits the pilot to:
- Initially set the NDU conditions
- Write a flight plan with up to nine waypoints
- Write or change the FROM/TO flight plan leg
- Do a test of the NDU panel lighting and displays
- See the ARINC-429 data from each of the three IRUs
- See the aircraft's position with relation to the waypoints
- Write the position and heading data for up to three inertial sensors
The control/display panel of the NDU has a power switch and an amber FAULT indicator. The power switch sets the NDU to ON or OFF. The FAULT indicator comes on when the built-in test equipment(BITE) finds an internal failure. The NDU also has four keyboards and two alphanumeric displays.
System Operation
The NDU provides the following functions:
- Entry of position and heading for all 3 IRSs
- Entry of position for up to nine waypoints
- Selection of FROM/TO leg
- Display of selected data from each IRS
- Position initialization
- Self-test front panel operation
- Display of flight plan and IRS outputs on the EFIS
The NDU is interfaced to the three IRUs and the three IACs via ARINC 429 data buses. This interface enables the NDU to control the IRUs and provides the link for data from the NDU to the EFIS.
Selection of the NDU as the navigation source on the EFIS is done by pressing the FMS switch on the PFD controller. Pressing the FMS switch toggles the navigation source between FMS 1, FMS 2 and LTRK on the PFD and MFD displays. The NDU operates on 28 VDC, which is provided by IRS 1, 2 or 3.
The NDU is operated by using data entry, special function, system select, and data select keyboards.
Data Entry Keyboard
The data entry keyboard consists of 12 keys that are used to enter, display, modify or transmit initialization, leg change and flight plan data.
The [ENT] key is used to accept entered data that is being displayed on the data display. This key contains a green cue light to indicate when operator action is required.
The [CLR] key is used to remove the entered data and clear the display. This key contains a green cue light to indicate when operator action is required. The NDU enters the error mode from the data entry mode as a result of an incorrect entry. When this happens, the CLR cue light flashes, the ENT cue light turns off, and no data can be entered. If [CLR] is pressed, the NDU exits the error mode, clears the incorrect data from the NDU data display, turns the CLR cue light off, and returns to the display mode.
The [BCK O] key is used to select the number and position of the previous waypoint for display when the WPT cue light is lit.
Special Function Keyboard
The special function keyboard consists of [M T], [BRT DIM] and [TST] keys.
The [M T] key is used to select a magnetic or true north heading reference. The key contains two cue lights, one for M and one for T. The illuminated light indicates the heading reference used by the NDU. Each successive activation of this button will toggle the heading reference.
The [BRT DIM] key is used to control the lighting of the NDU. When the key is first pushed and held, the display intensity increases until the brightest level is reached. When this key is pushed and held a second time, the display intensity decreases until the dimmest level is reached.
The [TST] key is used to start a test of all NDU annunciators, cue lights and displays.
System Select Keyboard
The system select keyboard consists of the [1], [2], and [3] keys that are used to select data for display from IRS No. 1, 2, or 3. Each key contains a green cue light that lights when the data from that IRU has been selected for display.
Data Select Keyboard
The data select keyboard consists of eight keys that are used to select data for display. Each key contains a cue light that when lit, indicates what type of data has been selected for display. When the [WPT], [LEG CHG], [POS], or [HDG STS] key is pressed, the operator can enter new data or modify the data that the NDU is displaying.
The [WPT] key is used to build and display a flight plan consisting of one to nine waypoints. When this key is repeatedly pressed, the NDU displays the successive flight plan waypoints by number and position.
The [LEG CHG] key is used to define or change the current flight plan leg by displaying the FROM and TO waypoint numbers. The current leg must be defined before navigation data can be defined and displayed.
The [XTK DTK] key is used to select and display the crosstrack position in nautical miles and the desired track.
The [DIS TIM] key is used to select and display the distance and time to the TO waypoint based upon present position and current ground speed.
The [TK GS] key is used to select and display the current track and ground speed of the aircraft.
The [POS] key is used to initialize and display the aircrafts present position.
The [WD WS] key is used to select and display the current wind direction and speed.
The [HDG STS] key is used to display the current heading. When the selected IRU is in the align mode, the NDU displays alignment status. When the selected IRU is in the NAV mode, the NDU displays heading.
ON/OFF Switch
The IRSs supply 28 VDC to the navigation display unit. The ON/OFF switch is used to apply and remove power from the unit.
Displays
The NDU contains a data display and a FROM/TO WPT display.
The data display consists of two displays:
- Six-position display on the left and,
- Seven-position display on the right, each having degree, decimal and minute indicators
The FROM/TO WPT display shows the FROM and TO waypoint numbers of the current leg and the number of the waypoint defined by the position being displayed.
Fault Annunciator
The fault annunciator illuminates when the NDU built-in test (BIT) detects an internal problem.
PFD and MFD
The navigation source annunciations on both the PFD and MFD display LTRK when navigation source selected is the navigation display unit system. LTRK annunciation is magenta normally and is amber if pilot and copilot are using the same source.
System Interface
The NDU interfaces with all three IRSs and all three IACs on board the aircraft. The NDU transmits and receives the same type of data on each of its three connectors. Each connector interfaces with one IRS and one IAC. Connector J1 interfaces with IRS 1 and IAC 1, connector J2 interfaces with IRU 2 and IAC 2, and connector J3 interfaces with IRU 3 and IAC 3.
Signal Interface
The NDU receives the following inputs from each IRS:
- ARINC 429 bus (high speed)
- Primary parameters are: Latitude, longitude, heading, ground speed, wind speed/direction The NDU provides the following output to each IRU/IAC pair:
- ARINC 429 bus (low speed)
- Primary outputs are: Set latitude, set longitude, set magnetic heading, desired track, bearing to waypoint, crosstrack
Power Interface
- + 28 VDC operating power from IRSs
- + 5 VDC panel integral lighting power and open ground dimming discrete (provided on connector J1 only)
System Test
Set MSU switches for IRS 1/3/2 from OFF to NAV.
- Push NDU ON switch. Verify that:
- M cue light illuminates
- SYSTEM SELECT 1 cue light illuminates
- POS cue light illuminates
- DATA DISPLAY shows dashes (indicating valid data not available)
- Push BRT/DIM to adjust to desired intensity
Initialization
Enter present position to SYSTEM 1.
- Push SYSTEM SELECT 2 Verify that:
- SYSTEM SELECT 2 cue light illuminates
- DATA DISPLAY shows same latitude and longitude as for system 1
- Push SYSTEM SELECT 3. Verify that:
- SYSTEM SELECT 3 cue light illuminates
- DATA DISPLAY shows same latitude and longitude as for system 1
Test and Monitoring
Push TST switch. Verify that the following occurs sequentially:
- All DATA DISPLAY segments illuminate
- Green cue light cycles through all switches
- Yellow FAULT annunciator illuminates
During the test, all display elements will remain lit. After four seconds the annunciator and cue lights go on sequentially for one second each. At the end of the test, all displays, annunciators and cue lights return to their previous state.
If in normal operation, an IRS failure occurs in the selected IRS, dashes appear on the data display to indicate failure. Another IRU can be selected via the system select buttons. The system select button does not indicate IRS failure. NDU operating power is not affected by loss of an individual IRU, since NDU power is supplied via a diode isolated feed from each powered IRS.
There is no comparison done between the IRS parameters received from each IRS to assess correctness. The NDU processes only the source currently selected via the system select button. A LTRK FAIL advisory CAS message is displayed when the NDU has failed or has been selected off.