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Seventies F-111D was the first digital F -111 variant, as well as being the first ever digital tactical fighter, fitted with a Rockwell Mk.II avionic suite and Norden cockpit display set. The F -111D cockpit included a "glass" ADI, combined moving map/TFR display, dual HUDs and a digital radar display which included frame freeze capability. Unique among USAF variants, the F -111D was designed with an intended air-air role, and was to have initially carried both AIM-7G and AIM-9J MMs. In service, the aircraft was tasked with strike duties, as was its sibling variants. (USAF)
Technology Explained – F-111 AUP Update Pt 2
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New Tusks For The Pig
The F-111 Avionics Upgrade Programme Pt I
The General Dynamics F-111, affectionately termed the “Pig”, is one of the RAAF’s most important assets. These aircraft are Australia’s strategic deterrent, and are tasked with long range land and maritime strike roles. In the event of hostilities, these aircraft would carry the fight to the enemy, destroying targets deep in hostile airspace and threatening hostile shipping to a substantial radii. While the F-111’s superlative combat radius and high aerodynamic performance are key aspects of its ability to perform its demanding roles, its avionics suite is no less important. The aircraft’s offensive avionics, comprised of sensors and navigation equipment, are critical to the aircraft’s ability to locate, identify and successfully attack its targets. The defensive avionics, on the other hand, determine whether the aircraft will survive its incursion into contested airspace, to fly and fight another day. When it was first deployed in the late sixties, the F-111 carried the most complex and technically sophisticated avionics systems ever fitted to a tactical aircraft. This complexity translated into substantial support costs, moreso since the system was largely built with analogue electronics which as a technology are somewhat temperamental. As time progressed, the maintenance of this equipment became increasingly expensive, and by the late 1980s the pressure to upgrade the RAAF’s aircraft became substantial, particularly as the USAF was expected to convert all of its remaining analogue models to contemporary digital equipment. Cost and operational readiness pressures forced the USAF to upgrade, and some indication of the scale of the support problem can be gained from published US figures (1981) which indicated that the SAC FB-111A had an aggregate aircraft MTBF of 2.2 hrs (still somewhat better than the USN A-6 with an MTBF below one hour). The digital refit of the USAF fleet would have made many analogue spares effectively unobtainable. In seeking approval for an upgrade to the F-111 avionics, the RAAF was largely constrained to retaining existing capabilities, the opportunity to substantially enhance the aircraft’s capabilities was unfortunately not to be exploited. The upgrade programme is thus focused on replacing sixties avionics technology with contemporary equipment of broadly similar capabilities, with the objective of greatly increasing reliability and reducing maintenance costs in the latter period of the aircraft’s life cycle. Incidental gains have been made, in that contemporary navigation equipment is substantially more accurate, and a digital weapon system can be easily adapted to accommodate new munition types. Aircrew workload is also reduced, as 1990s avionics provide for a greater degree of automation. Given the technological complexity required to support the various sensors, munitions, flight profiles and delivery modes inherent in the platform, an avionics upgrade of this scope is not a technically trivial exercise, as some would have us believe. Every major weapon system integration programme in the last several decades has been a protracted affair, this is simply the nature of the process. Where dozens of avionic black boxes need to be functionally melded by hundreds of thousands of lines of computer software, in order to create the illusion of a single weapon system, there are simply no easy shortcuts. To believe otherwise is to defy engineering intuition as well as historical experience. In 1990, the RAAF contracted Rockwell Electronics (Australasia) to upgrade the F-111C and RF-111C avionic systems, replacing the Mk.II analogue weapon system with contemporary digital equipment (NB: the RAAF’s four F-111A airframes have already been retrofitted with the “big” wing and FB-111A undercarriage, thus effectively converting them to F-111C airframes). Choice of prime contractor was substantially influenced by Rockwell’s then very recent experience with the F-111D/F Pacer Strike programme. Rockwell’s first involvement with the F-111 was in the late 1960s, when they developed the offensive avionic systems for TAC’s F-111D and SAC’s FB-111A aircraft, followed by work on TAC’s F-111F. The F-111D’s Mk.II avionics system was a particularly important technological milestone, as it was the first ever wholly digital airborne weapon system fitted to a tactical aircraft. The nucleus of the Mk.II avionics system was a digital computer, with most weapon system functional integration performed by software. The F-111D’s primary sensor, the largely digital AN/APQ-130 attack radar, was also designed by Rockwell. Rockwell as associate contractors thus created the Mk.II weapon system for the F-111D, and later the Mk.IIB weapon systems for the FB-111A and the F-111F. The latter system was blooded during the 1986 El Dorado Canyon mission to Tripoli, and most of the aircraft used in the Gulf would have still carried this equipment. It was therefore no surprise to the technical community that Rockwell subsequently won the 1989 USAF Pacer Strike contract to upgrade the USAF’s F-111D/F fleet with a new build offensive avionic suite, replacing the Mk.IIAIB systems. The Pacer Strike upgrade replaced the AJN-16 digital bomb nav, the AYK-6 computer and a miscellany of cockpit displays with a pair of 64 kWord Singer-Kearfott AN/AYK-18 Mil-Std-1750A digital computers, the AN/ASN-41(LN-39/H423) Standard Inertial Navigation Unit (SINU), cockpit MultiFunction Displays (MFD) and an Integrated Communication Navigation Identification System (ICNIS), all tied together by Mil-Std-1553B databusses. Initially Pacer Strike covered 79 D models and 84 F models, but this was subsequently cut to 58 F models, after the collapse of the USSR and the onset of subsequent force reductions.
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