The Litton LTN-72RL implements a complete Area Navigation System (ANS). On the actual aircraft, the ANS consists of:
For the INS simulator integration I will emulate the INU and attach to the actual CDU and MSU. In a typical installation the CDU would be mounted on the center pedestal or the forward electronics pedestal. The MSU would be mounted on the overhead panel. Each INU on board (most aircraft have two or three INUs) has a corresponding MSU and CDU.
To create a simulation of the LTN-72 my simulation software needs to interact with the CDU in a way that appears natural to the way pilots interact with the LTN-72RL. Talking to the LTN-72RL CDU is actually quite simple. The CDU sends data in the form of keystrokes to the INU and the INU in return sends data on how to paint the screens back to the CDU. See the image below:
The Litton LTN-72 system has quite a large number of screens that need to be painted by the simulation software. Here are the data pages that need to be simulated and integrated in a way that they can interact with the flight simulator:
Below is a short video showing a simple READ and WRITE test from the ARINC interface to the CDU. Data is being read on ARINC 575 label 030 and written with 21 labels starting at label 0200.
- Inertial Navigation Unit (INU)
- Computer Display Unit (CDU)
- Mode Selector Unit (MSU)
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| Litton LTN-72RL CDU and MSU |
For the INS simulator integration I will emulate the INU and attach to the actual CDU and MSU. In a typical installation the CDU would be mounted on the center pedestal or the forward electronics pedestal. The MSU would be mounted on the overhead panel. Each INU on board (most aircraft have two or three INUs) has a corresponding MSU and CDU.
To create a simulation of the LTN-72 my simulation software needs to interact with the CDU in a way that appears natural to the way pilots interact with the LTN-72RL. Talking to the LTN-72RL CDU is actually quite simple. The CDU sends data in the form of keystrokes to the INU and the INU in return sends data on how to paint the screens back to the CDU. See the image below:
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| INS Simulator Topology |
The Litton LTN-72 system has quite a large number of screens that need to be painted by the simulation software. Here are the data pages that need to be simulated and integrated in a way that they can interact with the flight simulator:
- Position (POS) - shows present position in Longitude and Latitude; Bearing and Distance from station; GMT and others
- Course (CRS) - displays the TO and FROM waypoints; the desired track and the cross track
- Track Leg Change (LEG) - permits the entry of FORM and TO waypoints; leg change entry; automatic and manual selection
- Waypoint (WPT) - provides pages for waypoint entry and route entry
- Flight Plan (FPL) - here we will enter waypoints and compute the flight distance
- Direct To (DIR) - enter data to fly direct to
- Instrument Data (DATA) - shows the INU data for heading; track; groundspeed; true airspeed; wind and along track acceleration
- Catalog (CAT) - provides pages displaying a station catalog; airport catalog; waypoint catalog; route catalog; location stations and a way to update catalog data
- Remote Ranging (RMT) - enables remote data from another INU unit, or the cross-filling of data from one INU to the others.
- Status (STS) - Provides information on IMU alignment status, time to NAV mode and other action codes
Below is a short video showing a simple READ and WRITE test from the ARINC interface to the CDU. Data is being read on ARINC 575 label 030 and written with 21 labels starting at label 0200.
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