IASSF: A Simulation For F/A-18 Avionics Software Testing. Paul Harbison; Clayton Newland BAE SYSTEMS, Building 169 WilliamTown RAAF BASE Paul.Harbison@baesystems.com.au Clayton.Newland@baesystems.com.au Abstract. The Integrated Avionics Systems Support Facility (IASSF) provides a simulated environment to test F/A-18 avionics, avionics software and system behaviour on the ground without the initial need for real F/A-18 flight testing. The Royal Australian Air Force (RAAF) has commissioned IASSF to allow mission critical Operational Flight Programs (OFPs) in the F/A-18 to be written, modified and tested. IASSF uses an automated and distributed architecture that has been developed to integrate the F/A-18 avionics with each other in a laboratory environment to allow the testing of the avionics software and hardware. Software models have been written to simulate avionics that cannot be stimulated correctly on the ground. IASSF contains a simulated tactical environment that allows simulated enemy aircraft to be targeted via Radar or FLIR, and simulated missiles to be launched. Intercommunications between the avionics and software models can be recorded and replayed to allow the automation of complex tests. The simulation parameters can be forced to values out of normal range to allow boundary testing of software. BAE SYSTEMS has delivered the IASSF to the commonwealth and is currently in a support phase for both maintenance and development. 1 INTRODUCTION In 1985, the Royal Australian Air Force (RAAF) purchased 75 F/A-18 Hornet fighter jets from McDonnell Douglas. The RAAF identified a need for an indigenous capability to modify the F/A-18 software and hardware. Changes made to the F/A-18 configuration require extensive testing before being released for flight. An integrated ground based testing laboratory was identified as the most cost effective way of providing this capability. This significantly reduces the need for expensive flight testing, and provides a platform for safely testing modifications. The IASSF laboratory aims to provide a facsimile of a real F/A-18 aircraft within a laboratory. The major avionics, mission computers and interconnections of the F/A-18 are replicated in the laboratory. IASSF uses simulation for testing of avionics and avionics software. The simulation is integrated so that all facets of the avionics can be tested together, providing the same stimulation as the real F/A-18 in flight. IASSF is a world class facility, offering US and non-us companies access to test F/A-18 avionics in an integrated laboratory. There is no similar integrated testing capability in the US. The US Navy tests all their changes on individual test stations before integration testing on the real F/A-18. The IASSF contract was awarded in 1992 to Easams. Ultimately, Easams was bought by GEC Marconi which then merged with British Aerospace to form BAE SYSTEMS. The BAE SYSTEMS headquarters is located in Adelaide, however Williamtown RAAF Base in New South Wales now has a significant work force to primarily support the Military Air Support division s Hawk Lead In Fighter and F/A-18 support programs. IASSF is one part of the F/A-18 support program, and consists of two sections. One section provides F/A-18 Operation Flight Program (OFP) support and the other section provides upgrades to IASSF. 1.1 OFP Section IASSF s OFP section modifies and tests the OFP software and delivers the changes to the RAAF. The first OFP modifications have been delivered and flown on the F/A-18 fleet during 2003. 1.2 IASSF Upgrade Section IASSFs Hornet Upgrade section performs upgrades to the IASSF as part of the Hornet Upgrade program, nicknamed HUG. HUG involves the upgrading of F/A- 18 avionics including new radars, new mission computers, new pilot displays and Electronic warfare systems. The HUG program is continuing over many years. 2 APPLICATION OF IASSF The OFP section is the long term user of IASSF and utilises IASSF s OFP generation capability as well using IASSF for integration testing. The OFP section uses IASSF to perform the three main tasks:
2.1 Modification and Testing of OFPs. OFP change requirements are prioritised by the RAAF before being implemented and integration tested by the OFP section. Software changes made to the OFPs may include incorporation of new missiles and weapons, improvements to existing pilot interfaces, and enhancing OFP behaviour. The Mission Computer (MC) and the Stores Management Processor (SMP) are the two target avionics OFPs that are currently undergoing software development. The SMP and MC OFP source code, compiler and processes have been obtained from the US Navy and McDonnell Douglas and duplicated in IASSF. Due to the vintage of the F/A- 18, the MC OFP is written in CMS-2M, ULTRA16 processor machine language, whilst the SMP OFP is written in 8086 machine code. The MC is main controller for all F/A-18 subsystems. If the MC fails, very few of the avionics are effective. Therefore there are two redundant MCs to provide failsafe capability. To effectively test the MC OFP, IASSF must provide simulated data to all MC inputs. The simulation of these avionics is the most complex task that IASSF performs. Testing of the MC OFP is complicated by the need to ensure that there are no negative impacts to the multitude of MC interfaces. The SMP is responsible for weapon management. SMP OFP changes require a full simulation of missile/bomb release and jettison for complete integration testing. Weapons are inherently expensive items to fire, whereas a simulation can be run repeatably at much reduced cost. Due to the explosive nature of some weapon release mechanisms as well the risk posed by having live explosives in a laboratory, the wing pylons, rack/launchers, weapons and all explosive devices are simulated by a system called SMP Real Time System (SMaRTS). This simulation allows the SMP to be stimulated as if real weapons are being fired to provide testing as close a possible to real flight. displays. The ALR-2002 was stimulated by actual Radio Frequency (RF) from IASSF s EW test station. The test station took data from the tactical environment simulation which provided latitude and longitude data for emitter locations. RF was generated that was representative of radiation that would have been received by the aircraft s antennas. The ALR-2002 then analysed the RF to predict the properties of the RF emitters. The emitter properties were then sent to the MC and pilot displays. This end to end testing, provided by IASSF, allowed the determination of the ALR-2002 compatibility with the F/A-18. 2.3 Analysis and investigation of existing problems found on the F/A-18. IASSF can be used to characterise issues experienced by the RAAF pilots and maintenance crews. These issues can be reproduced and analysed in the IASSF laboratory and corrective actions deduced. External organisations like the Defence Science and Technology Organisation (DSTO) have also used IASSF to provide and gather data for the F/A-18. 3 AVIONICS STIMULATION BY SIMULATION IASSF uses simulation for testing OFP software and avionics hardware, rather than the traditional use of simulation for human training. The IASSF laboratory is Integrated with all major F/A-18 avionics connected together. The IASSF aircraft can simulate a full F/A-18 mission including: taxi, accelerate, take off, fly, locate EW emitters, locate air and ground targets using the Radar and FLIR models, lock up targets and simulate missile and weapon launches. Although IASSF does not have a real cockpit, nearly all the real avionics displays and switches, available to a F/A-18 pilot, are installed. IASSF provides the OFP section with the capability to perform repeatable and deterministic testing of OFP changes. After integration testing at IASSF, new OFPs may then be released to the RAAF s Aircraft Research and Development Unit (ARDU) for flight test. Following successful completion of flight testing the IASSF OFP section releases the OFP to the RAAF. 2.2 Integration testing of new hardware New avionics that are being considered for use with the F/A-18 can be connected to IASSF and tested. Several new missiles and weapons, Electronic Warfare (EW) avionics and new FLIR avionics have been tested with IASSF. These new avionics have been integration tested with the existing F/A-18 avionics and OFPs, to ascertain their compatibility with the existing F/A-18 configuration. For example, when the BAE SYSTEMS ALR-2002 Electronic Warfare avionics was tested with IASSF it communicated to the MC and provided data for the pilot Figure 1 IASSF Operator Console Figure 1 above shows the IASSF Operator console, stick and throttle, avionics displays and out of window visualisation. IASSF houses approximately twenty F/A-18 avionics. The avionics power, analogue I/O, digital I/O, cooling air, and MIL-STD-1553 interfaces are controlled by VME VxWorks computers.
To test the MC and associated OFP, IASSF must stimulate the MC with the same inputs as it would receive in a real aircraft. IASSF achieves this by the stimulating the MC inputs directly using both simulated avionics and stimulation of real avionics connected to the MC. IASSF employs a data driven distributed architecture and a real time simulation to provide deterministic behaviour. To achieve this IASSF integrates 5 primary functions which are: 3.1 Simulation IASSF simulates F/A-18 airframe dynamics using a Commercial Off the Shelf (COTS) flight simulator called FLSIM. This provides the flight simulation and airframe data to the software models that then provide the information to the MCs. FLSIM provides modelling of the flight surfaces and takes input from the stick and throttle and supplies flight information such as roll, pitch and yaw. It provides a visual out of window display to allow the operator to fly. 3.1.2 Real Time The IASSF simulation is performed in a real time deterministic environment. The iteration rate of IASSF is governed by the Mission Computer. All software models and I/O processing need to run at the Mission Computer s iteration rate. A real time operating system called VxWorks is used to guarantee that all software completes running within the iteration rate time frame. The processing is distributed amongst 14 CPUs located in various VME racks. Synchronized timestamps are provided by IRIG-B, and reflective memory is used to provide shared memory between the nodes and real time event synchronisation. Asynchronous events that occur on both the avionics MIL-STD-1553 bus and physical wires are handled via interrupt routines on VME and processed as needed. 3.2 Stimulation A COTS tactical simulator called STAGE provides computer generated forces and operating environment simulation. STAGE provides wind, magnetic variation, air and ground based target data, EW emitters, VOR/ILS and TACAN navigation aids data to various avionics software models. 3.3 Instrumentation Other special attached devices provide simulations, such as SMaRTS which simulates weapons/stores, and EW RF which simulates RF emitters. 3.1.1 Software models Various avionics subsystems are simulated due to the difficulty in using the real avionics. The operator can choose to use real avionics or the equivalent software models. Software models are used for two reasons. One, some real avionics cannot be stimulated as they would be in the aircraft. For example the Inertial Navigation System (INS) uses gyros to detect changes in acceleration. It would be quite difficult to simulate the acceleration changes in the laboratory, so a software model was written that provides the same interfaces as the real avionics. Some of the other models that are provided as well as the real avionics are the Flight Control Computers (FCC), Radar System and Forward Looking Infra-Red (FLIR) Pod. The second reason is to allow the operator to override values and introduce errors in the MIL-STD-1553 data. Part of system testing software requires that the OFP to be tested is stimulated outside of normal bounds. It is difficult to override MIL-STD-1553 data values from real avionics, so software models have been written in place of real avionics. IASSF uses the simulated data to stimulate the real F/A- 18 avionics boxes in order to reproduce conditions experienced during real F/A-18 aircraft operations. IASSF allows the operator to override input parameters to the avionics for both digital and analogue I/O interfaces. IASSF provides facilities for monitoring interconnections between avionics equipment (MIL- STD-1553 MUX and other digital data busses, analogue and digital I/O). Internal CPU execution and state of selected avionics systems can be monitored and recorded by various mechanisms. This monitoring can be controlled interactively during test runs, or recorded for later analysis using IASSF s post test analysis capabilities. 3.4 Analysis IASSF provides a computer aided tool-set to support Post-Test Analysis requirements. The tool-set fuses data from all instrumentation sources (MIL-STD-1553, digital I/O, analogue data, etc) into a single coherent data-set. 3.5 Replay IASSF provides mechanisms by which previously recorded operator or system actions can be re-injected into the system to replay a test run. For example: the operator may interactively fly the system and record stick and throttle position, which are replayed during a later test run. Tasks may be controlled from predefined scripts, which provide a further deterministic and repeatable control mechanism. 4 IASSF PHYSICAL ARCHITECTURE The IASSF software and hardware design has shown itself to be a robust and scalable architecture that has
allowed HUG changes to the laboratory with minor changes to the core systems. New avionics and software have been integrated into IASSF with little or no architectural changes. The architectural design is not aircraft specific and could be applied to other avionics platforms where a laboratory environment is required to verify and validate the software and hardware of such an avionics platform. Figure 2 below details the interconnection between the Mission Computers and some of the other avionics. Figure 3 IASSF Block Diagram The Shared Memory Ring which encapsulates the physical reflective memory ring and implements the publisher/subscriber model to allow the different computing platforms to share data. The Shared Memory Ring also provides the real time event that schedules all real time processing. Figure 2 MC and Avionics Block Diagram IASSF employs four different computing platforms. PCs are used for normal office applications, VME VxWorks for real time applications, SGI for COTS flight simulation and tactical environment, and HP- UNIX for user interface. The VME, SGI and HP-UNIX computing platforms within the laboratory are connected via a shared memory ring and Ethernet. Figure 3 below shows a block diagram of the IASSF laboratory detailing how the physical components interface together with the real avionics and mission computers. The IASSF design provides an architecture where processing tasks and functionality are distributed amongst the various computing platforms to best utilise the computing capabilities of each platform. Each platform performs different tasks that are synchronised with the simulation real time event cycle. The key design components to the IASSF physical architecture are: The Physical IO System which interfaces to the avionics physical wires in real time. A publisher/subscriber model is used where avionics input wires are stimulated using values read from the shared memory ring (subscribed), and avionics output wires are written to the shared memory ring (published). The Command Distribution System which enables the various entities within the system to be commanded in non real time, to perform particular functions or tasks. (Eg Turn on a particular piece of avionics required for a test). The system uses Ethernet to communicate to the various computing platforms that contain the entities. The Avionics Bus Interface System which interfaces to the avionics MIL-STD-1553 bus that is used by the MC to communicate to the various avionics. The system provides the capability to perform bus monitoring/recording and, remote terminal and bus controller emulations. 5 FUTURE The F/A-18 is proposed to fly until 2012 when it is anticipated it will be replaced by the Joint Strike Fighter (JSF). Investigation is continuing to determine if an IASSF type laboratory will provide Australian specific software upgrades for the JSF. IASSF is being used to support integration of the Advanced Short Range Air to Air Missile (ASRAAM) to the F/A-18. Integration testing of the ASRAAM will be achieved by using IASSF. New Electronic Warfare (EW) avionics are being chosen as part of the HUG. IASSF may play a pivotal role in the integration of the new EW avionics into the F/A-18. IASSF will continue to be upgraded in the near future with new HUG avionics, including Helmet Mounted Cueing System, colour cockpit displays, and data link capability, in line with the F/A-18 fleet.
6 CONCLUSION IASSF has provided the Royal Australian Air Force the capability of making in country modifications to the software and hardware on the F/A-18. IASSF allows software development and integration testing to be conducted within the laboratory, reducing the need for expensive flight trials. The architectural components used in IASSF are very flexible and could be utilised on any future avionics system. IASSF provides a world-class simulator for avionics software testing, defect investigation, and integration of new avionics. REFERENCES 1. Traynor, Grant. (2001) Technical Performance Parameters of the IASSF Architectural System. BAE SYSTEMS.