THE CORE OF THE INTEGRATED vehicle and mission management system (IVMMS) is made up of two commercial systems processors (SPs), with "militarised" software. The SP's hardware is based on that of the Lockheed Martin C-130J, with 85% software commonality.
The SPs dual-redundant Mil-Std - 1553B data buses - interfacing with the three control and display units (CDUs), a 1553B avionics bus, four high-speed Arinc 429 buses (for commercial equipment such as the electronic flight-instrumentation system - EFIS- and weather radar), and have interfaces for databus-incompatible avionics. They act as mission computers (including conventional FMS functions.)
A "zeroise" switch, when operated for 5s, will clear all databases and pre-sets and plans from the global-positioning system (GPS) and SPs, to ensure post-flight security. Provision of a dual attitude-and-heading-reference system (AHRS), but a single inertial-navigation system (INS), was a budgetary decision. The H-423 INS may be used as a third attitude-source.
In 500h of test flying, an overall accuracy of 0.2-0.5km (0.1-0.3nm) was achieved. The prime navigation sensor is the MAGR 300 GPS. This has a military accuracy of 15m when used with the INS. The navigation-mode hierarchy includes four main INS/GPS levels, with Kalman filtering - and five INS/AHRS configurations with radio navigation and specific filtering. Manual-position updates are possible only in dead-reckoning mode, using raw INS; the only GPS control is reset.
Control of radio communications and navigation radio-aids through the CDUs, uses a similar format to that of the individual integrated radio-management units fitted to many civil aircraft. Dedicated control of VHF1 and VOR 2 is provided, in case of major avionics failure.
There are 40 pre-sets each, for communications, radio-navigation and ADF frequencies - identified by frequency or designator. VORs and tactical air-navigation systems (TACANS) at the same sites can be paired radio-electronically. The TACANs still figure more in military navigation, because of higher performance - and use of mobile TACAN stations.
Through the CDUs, the crew can also disable or reconfigure elements of the avionics system - such as that of attitude-EFIS sources. A message light will show in the case of an automatic reconfiguration.
FMS memory allows a maximum of 200 custom waypoints, 100 flightplans - or 1,299 waypoints with altitude restraints. Up to ten database navaids can be temporarily inhibited for a mission. Up to five mark locations can be entered in flight - their accuracy has been improved with GPS.
The entire world database occupies 1.2 megabytes of data, and multiple data-cartridges can be used to load both this and mission data into the SPs. Ballistic data cover up to 20 parachute types.
The CDUs contain patterns for holds, the computed air-release point (CARP) and search and rescue (SAR).
The holding-pattern default inbound leg time is 1-1.5 min The three SARs are creeping line, sector and expanding square. On acutely angled SAR entry, an initial waypoint is created, to allow for the angle of intercept and turn needed. SAR patterns can be adjusted for spacing and direction of turn. Three CARPs can be defined, and each can be inserted between any two waypoints in the mission plan; the sub-route to the CARP initial point is called up at a leaving waypoint.
Low-altitude drops with the CARP are defined for personnel and/or parachute/ heavy sled-drops: high-altitude drops are made with personnel only. Details entered define the drop zone, heading and the number of runs. The calculation of the release point to achieve the impact point is based on drop type, load definition, high or low release, use of door or ramp, drop speed and chute type
The FDD's bottom two lines inform the pilots as the drop zone is neared. Alerts are given at 20min, 10min and 6min and at slowdown point; at 1min final alert, the aircraft must be stable - or an abort warning will be given - wind out of limits will also result in a warning. The drop countdown is in seconds: 10, 5, 4, 3, 2, 1. GO (plus green light). NOGO and ESC (plus red light) may appear in the drop zone.
The CARP Progress page on the CDU is used for late interventions - a recheck on forward travel and drift in drop. Ground data can be re-computed until final track - up to 1min before the green drop-light; air data is assessed until 30s before drop.
Source: Flight International
