USA   F-111 Aardvark


Republished by with the express permission of Carlo Kopp.  More articles here.

F-111 Upgrade Options

Part 1 Status Quo

by Carlo Kopp
Article published in Australian Aviation, 1998
Copyright   (c) 1998 Carlo Kopp

The RAAF's Strike Recce Group (SRG) comprising 36 F/RF-111C/G bombers is without doubt the ADF's most potent asset, capable of projecting air power against maritime and surface targets to combat radii of 1000 NMI from land bases, without inflight refuelling. In the low threat density and technologically unsophisticated broader regional air environment of the last two decades, the F-111 was until recently unchallenged.

Current ADF planning sees the F-111 as a frontline combat asset in service until 2020, with the SRG winding down and consolidating F-111 operations from about 2015 onward.

Purchased during the sixties and delivered during the mid seventies, the F-111C carried an analogue nav-attack system and for the period a capable defensive package. During the eighties the aircraft were further modified to accommodate the then state of the art podded AVQ-26 Pave Tack thermal imaging laser equipment, for the delivery of laser guided and dumb bombs, form all altitudes. This upgrade also saw the capable Harpoon ASCM integrated on the aircraft.

The original F-111C Pave Tack/Harpoon "classic" avionic system was a unique hybrid and cumbersome to maintain. The RAAF fought long and hard during the late eighties to secure funding for a digital nav attack system, which would be supportable with spares, much cheaper to maintain, much more reliable and capable of later accommodating the new generation of "smart" munitions. The new system was installed under the Avionic Upgrade Program (AUP), and was originally permitted only to improve maintainability - the then DoD bureaucracy vehemently opposed any capability growth on the F-111.

The AUP offensive avionic system is built around a dual redundant pair of AP-102A mission computers, a pair of AN/ASN-41 Ring Laser Gyro Inertial Navigation Systems supplemented by a MAG-R GPS receiver, includes a pair of digital cockpit displays, and a digital Stores Management System (SMS) common to the F/A-18. The core offensive avionic upgrade was supplemented by incremental upgrades to the existing AN/APQ-165 real beam mapping analogue attack radar (ARS) and the vital AN/APQ-128 Terrain Following Radar (TFR), bringing them up to the AN/APQ-169 and AN/APQ-171 configurations respectively. A wholly new Digital Flight Control System was fitted.

An important result of the AUP program is that the new avionic system provides a defacto Mil-Std-1760 "smart" interface to the four swivel pylon weapon stations, enabling the integration of virtually any modern "smart" weapon. The only non-compliance with the Mil-Std-1760 interface lies in the provision of a lower power feed voltage, a feature common in many Mil-Std-1760 implementations and usually accommodated by weapon designers.

At this time much of the AUP production phase upgrade has been completed and it is expected that the last aircraft will be finished within the next 12 months. All indications are that despite some modest delays in the early phase of the AUP program, the upgraded aircraft are delivering superb reliability and accuracy well in excess of the specified requirement. From a technological perspective, the AUP is an outstanding success for the RAAF and one which will significantly improve the aircraft's operational availability, while reducing aircrew workload and improving system accuracy.

The fifteen F-111G aircraft, acquired during the early nineties by the previous government, are to be upgraded with a new generation digital avionic package to bring them to a similar standard to the F-111C, and allow them to deliver guided munitions. The aircraft as delivered have a very accurate older generation digital offensive avionic suite, which is however no longer supported, and cannot integrate guided weapons. Funding has yet to be approved, the configuration of the upgrade, under program AIR 5404 Phase 2 (Precision Weapons Modification), was at the time of writing still in the process of being decided. AIR 5404 was scoped to support only capabilities extant in the F-111C AUP.

The retirement of the F-111 from USAF service has been a mixed blessing. The dismantling of the USAF's support infrastructure means that many facilities, such as that for cold proof testing, have to be recreated in Australia to allow ongoing operation of the aircraft. On the plus side, this means that Australian industry will benefit significantly, and we also now have access to an almost inexhaustible supply of spares parked at the Davis Monthan AFB boneyard. Needless to say the RAAF have been busily buying up whatever components the USAF did have in stock, often at bargain prices. Some components with limited shelf lives, such as pyrotechnics, will have to be custom manufactured to provide ongoing support.

While being the sole operator of the type means that we no longer have the USAF's logistical system to rely upon, it also removes the constraints of having to comply closely with USAF aircraft configurations to chase the arguably illusory cost savings of commonality.

Current Upgrade Programs

One benefit we have seen from the winding down of the USAF fleet is the availability of later built, slightly higher thrust powerplants. The RAAF will be refitting its fleet of aircraft with the TF-30-P-109 engines used previously in the F-111D and EF-111A, for the F-111C this is an almost "drop-in" replacement, for the F-111G this will produce a hybrid engine using the P-109 fitted with the "straight" tailpipe of the FB-111A/F-111G P-107 engine. The P-109 engines will provide a slightly higher level of thrust for improved combat and takeoff performance, and arguably some improvement in reliability since they will not be "driven" as hard as the older engines to meet currently required aircraft performance. The use of a common engine across the C and G models will save money in supporting the type, indeed this was the primary driving argument behind the upgrade.

The biggest upgrade program in the pipeline for the SRG is the Echidna (AIR 5391 and 5394) program, aimed at providing the F-111 (and C-130H/J, S-70, CH-47) with a state of the art and architecturally common defensive suite. The aircraft in service carry the now obsolete and unsupported ALR-62 (V)5 (the (V) 6, 7 variants remain supportable for the time being) Radar Warning And Homing (RHAW) equipment, and a mix of ALQ-94 and ALQ-137 Defensive Electronic CounterMeasures (DECM) systems. Optimised to defeat the SovBloc IADS of the late seventies and early eighties, the ALR-62/ALQ-94/137 package was highly capable in its day, well matched to the Iraqi IADS of 1991, but by contemporary standards it is technologically obsolete and becoming rapidly unsupportable.

The intent of the Echidna program was to exploit if possible the DSTO developed ALR-2002 Radar Warning Receiver, a state of the art digital design providing world class performance and capabilities. The 2002 is to be complemented by a suitable jamming package, and expendables, and the system is to employ an integrated architecture allowing for optimal employment of expendables and jamming. Earlier disclosures indicate that the new system is to be effective against pulse mode, continuous wave, and monopulse threats, and is to include a Missile Approach Warning System (MAWS). Whether the RAAF will opt for a towed decoy has not been stated at this time.

The RAAF has been discrete about the specific configurations bid for Echidna, the program is running a little late primarily as it grew during its early life to accommodate shared configurations for other RAAF types. This has imposed a considerable burden in terms of program complexity in technology, integration and management. While the intent of saving taxpayers dollars through commonality was clearly well intended, in perspective this requirement may introduce considerable delays to IOC, clearly an issue for a front line asset such as the F-111. It is unclear at this time whether the RAAF will opt to continue with the program in its existing form, or alter the main plan to accommodate the F-111 separately from the remaining types. If replacement of the F-111's defensive suite is the first priority, then there would be considerable merit in splitting the F-111 requirement off from the slow movers in the program.

The issue will be in how to implement this without compromising the capability of the end product, since a stop gap podded DECM solution, at the time of writing being decided under the F-111 Interim EW Capability Requirement, will never match the capability of a well integrated internal suite. Well integrated here meaning a system with proper growth provisions, such modularity, and bussing and if applicable, waveguides of appropriate bandwidth.

While a podded solution does offer the flexibility of rapid replacement, it also adds drag, radar signature and ties up hardpoints, as well as typically having inferior angular coverage to a well designed internal suite. Pods typically cover only a nose and tail sector, and cannot effectively cover the critical upper hemisphere forward sector against fighter/AAM attack, unless carried on a wing station instead of munitions. Podded DECM was a Vietnam period "Quick Reaction Capability" measure which has persisted with the generation of aircraft designed in the period predating internal DECM systems.

The obsolescence and marginal tactical utility of the ALR-62/ALQ-94/137 package on the F-111 suggest that priority should be given to meeting the needs of the F-111 at the earliest possible time.

The second major upgrade program for the F-111 is the AIR 5398 guided munitions program, intended to provide the aircraft with a broad suite of modern weapons for use in reactive (ie self defensive) defence suppression (SEAD) and precision standoff attack against area and hardened point targets. The stated purpose of AIR 5398 is therefore to improve aircraft survivability in well defended environments. Until this program is implemented, the primary weapon of the F-111 will remain the trusty Paveway II Laser Guided Bombs (LGB). While these are cheap and effective weapons, they require that the aircraft close to within 3-5 NMI of the aimpoint which can compromise the aircraft's survivability by exposing it to SAM and AAA defences.

The RAAF has already committed to the Israeli designed Rafael AGM-142 Popeye (formerly Raptor) rocket propelled inertial/imaging/datalink guided standoff missile. The AGM-142 is in the initial phases of integration with the aircraft, and we can expect an IOC early in the next century. The AGM-142 outranges almost all area defence SAMs and is a highly accurate and lethal weapon, carrying either a unitary blast fragmentation warhead or a hardened case penetrator. The AGM-142 will be used for attack on heavily defended point targets, for lethal SEAD and as a heavyweight supplement to the Harpoon in maritime operations.

The AIR 5398 program was originally divided into several requirements, to provide an antiradiation missile for self defence, and a family of weapons for attacking other classes of target, using penetration warheads or submunitions. The intent was to exploit the capability of the new digital weapon system to support a wide range of munitions, and increase the aircraft's lethality and survivability. Clearly this was long overdue.

The result of the RAAF's initiation of AIR 5398 was a deluge of bids by US, European and Israeli vendors of guided weapons. In effect, almost everything in marketplace has been offered.

The RAAF has not been very forthcoming with information on the current status of this program, but it is known that it is currently being rethought to minimise the number of weapon types (ie airframes) to be acquired, in turn to minimise the cost overheads of software integration, clearance testing, logistical support and training. Until further disclosures are made, it is unclear exactly what package of weapons will be acquired to the meet the latter phases of the program. This in turn will determine the most likely contenders.

A major issue in the context of AIR 5398 is that of supporting targeting sensors on the F-111. The aircraft is at this time reliant wholly upon its sixties technology analogue low resolution real beam mapping attack radar, which is not adequate to the task of providing good identification of aimpoints prior to the launch of AGM-142s and likely other weapon types to be acquired under this program. This is not an issue for the US or Israelis, since both have high resolution SAR/GMTI radars for this purpose. The primary launch platform for the AGM-142 in IDF service is the upgraded F-4E, fitted with a Norden APG-76 SAR/GMTI radar, which has 3 ft square resolution at 30-40 NMI of standoff range.

Since the mooted Stand Off Imaging program (SOI), intended to fit several F-111s with a weapon bay mounted SAR/GMTI reconnaissance radar, is for all practical purposes dead at this time, the RAAF will not have the reconnaissance and targeting capability which is required to robustly target any of the standoff weapons which will be acquired under AIR 5398.

Targeting anti-radiation missiles or more lethal munitions for self defence (or SEAD) demands range known launch conditions if good standoff ranges and unambiguous targeting are to be achieved, and this suggests that a rangefinding receiver package will be a necessary supplement to the existing Echidna package.

There are further good reasons why both a SAR/GMTI and rangefinding receiver should be introduced on the F-111, and these will be discussed later.

Regional Developments

Clearly the AIR 5391 and AIR 5398 programs address many important capability and supportability shortfalls in the upgraded F-111 and its weapon suite. However, Australia's strategic position and available guided munitions and sensor technology have been evolving dramatically since these requirements were initially drafted. It is therefore a good idea to explore the resulting implications.

In the strategic context, we have seen the commitment by major players in the broader region to acquire large numbers of the Su-27SK and Su-30MK strategic fighters, tankers and AEW&C aircraft, supplemented by the latest Russian air-air missiles and SAMs.

In practical terms, this ratchets up the baseline capability of broader regional air defences. AEW&C/tanker supported Flankers means that round the clock CAP coverage can be provided out to respectable combat radii. The deployment of the Buk M1/SA-11 Gadfly, the S-300PMU-1/SA-10D Grumble, S-300V/VM / SA-12A/B/C Gladiator/Giant and the 9M331 Tor / SA-15 Gauntlet means that all altitude SAM coverage can be provided for high value targets with very modern weapons, all of which are fully mobile or semi-mobile.

The fighter/AEW/tanker capability will not mature for about a decade, since much training, support and doctrinal effort will need to be expended to match current Western competence in this area. However, as this capability matures, an F-111 will require a supporting fighter escort CAP to ensure that it can penetrate unmolested by fighters to weapon launch ranges, in its planned configuration. Penetration speed will also need to be increased, and this will incur a combat radius penalty if not offset by other measures. A better defensive AAM than the AIM-9M will also be necessary since its short range and cumbersome target acquisition are not credible in the face of the R-77 Adder and R-73/74 Archer.

The SAM and supporting radar capability in the broader region will mature much faster and we can expect a respectable capability by about 2005, since these weapons will directly slot into existing air defences and C3 networks, built around established Russian doctrinal and training systems.

We can also expect to see the first generation of Russian designed Low Probability of Intercept (LPI) radars deploying in the next decade, based upon evolved variants of existing Russian phased arrays. The Flanker is a likely first candidate.

This will require a major improvement in the capability of the F-111's defensive avionic package, since the warning system will need to have a defacto ESM capability to provide extended detection range and the ability to detect LPI threat radars. The increased mobility of the newer SAMs deploying regionally also means that strike supporting SEAD operations will have to be more responsive, the "prebriefed" mission profile will most likely be stale by the time the aircraft arrive in the target area. The implication of this is that an Emitter Locating System (ELS) or similar capability will be almost essential.

Weapons and Technology Developments

Without doubt the most important technology to deploy on a large scale in recent years are GPS guided bombs, glidebombs, dispensers, and supporting Synthetic Aperture/Ground Moving Target Indicator (SAR/GMTI) attack radars. The combination of SAR/GMTI and GPS guided bombs will supplant the thermal imager and Laser Guided Bomb in USAF/USN service as the primary sensor/weapon package for strike operations during the coming decade. The recent development of pseudo-differential (ie GAM/GATS) guidance techniques for GPS guided bombs, whereby the bombs are programmed to track the same satellites as the bomber, has improved accuracy to the point where the GPS guided bomb approaches or matches the accuracy of the LGB, with the benefit of multiple autonomous drops in a single pass through a solid overcast. Given that there is no cost penalty in mass produced GPS guided bombs, against LGBs, the LGB has now been outclassed in capability across the board. Moreover, anti-jamming antenna packages for such bombs are now rapidly approaching deployment, essentially nullifying the only reasonable technical argument against their wide scale use.

Wide Area Differential GPS (WADGPS) is now maturing, and will be a viable means of further accuracy improvement over the next decade. Accuracies better than LGBs have been demonstrated.

The US services are now committed to buying over 80,000 GBU-31/32 JDAM GPS guided bomb tailkits, to equip virtually all frontline fighters, including many types without thermal imager/ laser designator capability (

Importantly, GPS guided weapons do not lose accuracy with increasing launch ranges, and thus GPS has become an enabling technology for low cost standoff glide bombs and dispensers, which until now have been expensive due to the demand for highly accurate inertial systems. Aided by GPS, the cheapest RLGs (Ring Laser Gyro) become more than adequate. The US services are committed to the AGM-154 JSOW glide dispenser, and reports from the US indicate that there is growing interest within the USAF bomber community in a winged variant of the GBU-31/32 JDAM (producing in effect a JDAM based equivalent to the Australian Kerkanya proposal).

Weapons such as the JDAM, JSOW and any Kerkanya clones are not a substitute for the AGM-142 and similar powered weapons, since they are much slower, lack "operator-in-the-loop" high precision interactive guidance, and typically will not match the kinetic energy of a missile on impact. Moreover, their range is under most conditions inferior to a powered weapon. However, under many conditions they will be adequate, and costing under $50,000 per round (JDAM at USD 18k), come in at about 5-10% of the cost of a powered munition. Therefore, they are excellent in terms of bang per buck, and since they provide much less exposure of the launch aircraft to opposing defences, compared to laser guided weapons, they enhance survivability by a decent margin. This is especially true of glide weapons like JSOW and Kerkanya (or clones), which offer 40-80 NMI range for high altitude drops, and up to 25 NMI for a low level toss.

Other than weapons, another technology has blossomed very recently in the US. This is the use of adhesive applique laminates instead of paints for surface finishing the aircraft. The US is at this time gearing up for high volume production of such materials. While they offer better durability and cheaper application than camouflage paint, they also have another interesting characteristic. The laminate can be made of multiple layers, incorporating microwave lossy or radar absorbent materials. While a radar absorbent skin applique is not going to turn an F-111 into a B-2, it is a relatively cheap way of cutting radar cross section from major airframe features such as leading edges and nasty little corner reflectors. And every deciBel of RCS removed is one less deciBel for a threat radar to detect.

Another important technology which has proliferated in the last few years are highly capable Helmet Mounted Displays, which combine a helmet embedded night vision capability (miniature single chip thermal imagers or NVG tubes), with computer generated symbology, all projected on the pilot's visor. Such displays can be used to "fuse" radar warning threat data, radar tracks, status information, and flight information into a single display, and provide for cueing of air-air and air-ground guided weapons. In effect, many portions of the traditional "glass cockpit" and HUD can be presented on the helmet visor. This means that the latest sensor fusion and data presentation techniques can be seamlessly integrated into an arbitrary cockpit, without having to go through a costly rearrangement of cockpit displays and instrumentation, a particular issue with the congested F-111 cockpit.

Finally, we are beginning to see the deployment of compact and competitively priced precision direction finding and rangefinding receiver packages as adjuncts for fighter aircraft radar warning packages. These receivers allow the range known targeting of Anti-Radiation Missiles, significantly improving their standoff range and accuracy, as well as providing long range warning of threats hitherto impossible with low sensitivity radar warning receivers. With the trend to use Electronic Support Measures (ESM) class receivers as the baseline warning systems on fighters, the days of the conventional RWR are now numbered, especially with emerging Low Probability of Intercept radars.

The following three parts of this series will explore potential technology upgrades which could follow on the AUP, AIR 5391 and 5398 programs, intended to provide the F-111 with a credible and adaptable combat capability through to 2020, exploiting technology which is now becoming available.

The current F-111C AUP program equips the F-111C with a modern, dual redundant, digital nav attack system, with a pair RLG INS and a GPS receiver. The upgrade includes a digital stores management system, a digital flight control system, a pair of digital cockpit displays, and incremental upgrades to the attack radar and TFR. The AUP package provides the aircraft with a highly reliable, low maintenance and very accurate nav attack system, capable of supporting a wide range of modern smart munitions reliant upon digital weapon station adaptors.

The F-111G aircraft will receive a major upgrade to their weapon system to provide a capability to support smart munitions, similar to that in the F-111C AUP. Under project AIR 5404, the RAAF is at this time deciding upon the configuration of the upgrade. The existing older generation digital weapon system on the F-111G is much less capable than that on the F-111C AUP, limiting the aircraft to the delivery of dumb bombs.

The AGM-142 is a potent weapon for attacking well defended targets, and is employed for this purpose by the USAF and the Israeli AF. However, to perform in this important role, it must be provided with the prelaunch coordinates of the intended target. Without a SAR/GMTI capable attack radar or a rangefinding and direction finding receiver package, this can become a very difficult task. This AGM-142 is being launched by a B-52G of the USAF's 20th Bomb Squadron (USAF).

Without doubt the greatest weakness in the existing F-111C AUP/F-111G avionic suite is the absence of a modern Synthetic Aperture Radar / Ground Moving Target Indicator mode capable attack radar. The AGM-142 SOW and follow-on AIR 5398 standoff munitions will require such a radar for both supporting reconnaissance and effective inflight targeting of these weapons. This imagery was produced by the Norden APG-76 MMRS, which the Israeli Air Force use to target the AGM-142 from their upgraded F-4E Phantoms. The upper three images show Westover AFB at 45.8 NMI (18 metre resolution), at 43.7 NMI (9 metre resolution), at 37.8 NMI (3 metre resolution), the lower images show a tanker anchored in Delaware Bay at ranges of 40.1, 32.3 and 29.6 NMI and resolutions of 3, 1 and 0.3 metres respectively (Norden).

Pic.6 (JDAM - GIF cutaway)

The GPS/inertial guided GBU-31/32 JDAM will supplant the Paveway as the primary guided bomb on US fighter and bomber aircraft. The JDAM is an autonomous weapon which is loaded with the GPS coordinates of the target prior to release, and in its baseline configuration provides similar accuracy and cost to the Paveway, with the benefit of genuine all weather operation, and better range performance. The USAF are to soon deploy an enhanced anti-jamming antenna package, as well as pseudo-differential targeting techniques on synthetic aperture radars. There is growing interest in the USAF bomber community in the deployment of a winged variant of the JDAM, similar in concept to the DSTO Kerkanya demonstrator (Boeing). LOGO


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