VIGGEN UPGRADES: AJS 37 / JA 37D / SK 37E

Written by: Greg Goebel

Viggens in service have been given a continuous stream of mostly minor upgrades, generally in the form of improved avionics and software upgrades. One of the more important enhancements, performed in the late 1980s, was carriage on the AJ 37 of the US US-designed AGM-65A Maverick ASM, license built in Sweden as the "Rb-75". This generally replaced the less sophisticated Rb-05 ASM. A comparable upgrade, also performed in the late 1980s, provided support for the much improved AIM-9L Sidewinder "all aspect" AAM, built in Sweden as the "Rb-74".

In 1992 the Swedish government approved a program to upgrade a total of 98 AJ 37s, SF 37s, and SH 37s to a multirole "AJS 37" configuration, with "AJS" standing for "Attack / Jakt / Spaning". The rationales for the upgrade were to extend the utility of the existing fleet, as well as provide an aircraft that would familiarize Flygvapnet pilots with multirole operations before they moved on to the SAAB 39 Gripen multirole aircraft, then scheduled for introduction to service later in the decade.

The drivers for the upgrade was the development of new weapons for the Gripen, such as the the DWS 39 gliding submunitions dispenser, and in particular the Rb-15F antiship missile, a vastly improved derivative of the old Rb-04 fitted with a turbojet engine and new seeker. The Rb-15F was developed for the Gripen but was ready for service well in advance of the SAAB 39. As long as the weapon was available, there was absolutely no reason to not make use of it. It was determined that the old AJ 37 could carry the missile if the aircraft was fitted with a new Ericsson processor system and a MIL-STD 1553B digital databus. A little further thought showed that the same fit could be performed on the reconnaissance Viggens, and the result was the AJS 37.

Early press releases on the program gave the impression that the AJS 37 was to be a major upgrade, and that the 48 AJ 37; 25 SF 37; and 25 SH 37 aircraft upgraded would end up with a common configuration. This was reading too much into it, and the announced total of 115 upgrades was also something of an exaggeration. Basically this was a middling sort of avionics and software upgrade that did not change the external appearance of any of the upgraded aircraft in any significant way except to permit them to carry new stores. Changes to the cockpit control layout were modest and certainly did not involve fit of a true glass cockpit. There was no airframe service life extension program (SLEP).

The upgraded AJ 37, SF 37, and SH 37 machines acquired the new designations of "AJS 37", "AJSF 37", and "AJSH 37" respectively. All have the new processor and the MIL-STB 1553B databus; and all support a new mission planning system in which a cartridge storing a mission plan can be plugged into the aircraft, and then yanked out after the mission storing data on the flight that can be reviewed on a mission computer. Beyond that, the capabilities of the three types of machines retain considerable differences:

• The AJS 37 can carry the carry the DWS 39 and the Rb-15F, and it can also carry up to six Sidewinders, instead of the two carried previously. Its radar has also been upgraded to a similar or identical specification to that of the PS-371/A on the SH 37, allowing the AJS 37 to perform radar reconnaissance flights. However, it cannot carry external reconnaissance pods.
• The only really significant improvements in the AJSF 37 over the SF 37 are the mission planning system and the ability to carry six Sidewinders. It still cannot carry offensive stores. Although there was an impression early on that the upgrade would refit the SF 37 with a radar nose, it didn't happen, and it still retains the camera nose with no radar.
• The AJSH 37 has the same armament options as the AJS 37, but it can carry the Red Baron and LOROP pods.

Re-deliveries of upgraded aircraft began in 1993 and were completed in 1996. Dedicated reconnaissance squadrons were phased out and reconnaissance machines incorporated into regular attack squadrons. However, a special reconnaissance squadron of AJSF 37 Viggens was set up late in the decade to provide support for international peacekeeping missions, the Swedes having become a little more assertive in foreign military operations following the end of the Cold War.

As with other Viggens, the JA 37 interceptor Viggens have been continuously upgraded, in particular by being fitted with a datalink system in the mid-1980s. The Flygvapnet had developed the sophisticated STRIC ground-based defense datalink system, and STRIC allowed Viggens to be vectored onto targets without using their own radar, giving them an element of surprise. STRIC also allowed ground controllers to read simple aircraft status, and let pilots trade simple messages through the ground network. Other useful upgrades added multiple-target tracking to the PS-46A radar, and a automatic gunsight for the Oerlikon cannon that allowed it to be used in collision-course, as opposed to simple tail-chase, attacks.

In the late 1990s, a major upgrade program was implemented to convert surviving JA 37s to the "JA 37D" standard. Updates included:

• Carriage of the advanced Hughes AIM-120B Advanced Medium Range AAM (AMRAAM), a substantially improved follow-on to the Sparrow / Skyflash family with greater range -- up to 50 kilometers (31 miles) in optimum conditions -- and a vastly improved seeker system. The AMRAAM is known as the "Rb 99" in Flygvapnet service. The JA 37D can carry four AMRAAMs, not just two as with the earlier Skyflash AAM.
• A new Ericsson SAAB CD207 mission computer, as well as a new stores management computer.
• Radar updates to support AMRAAM and provide other capabilities.
• A new 15 x 20 centimeter (6 x 8 inch) flat-panel color tactical cockpit display, originally implemented for the Gripen.
• Improved countermeasures and counter-countermeasures, including an RWR update, fit of BOY 401 chaff-flare dispensers into the inner wing pylons, and carriage of the U95 jamming pod.
• A TARAS encrypted digital tactical radio system, with advanced networking capabilities allowing the Viggen to interact with the Gripen or a SAAB Erieye airborne warning and control system (AWACS) aircraft.
• A new mission planning system. It is unclear if this is the same system developed for the AJS 37 upgrades.

The JA 37D upgrade program was initiated in 1992, with the conversions beginning in the late 1990s. It is unclear how many JaktViggens were converted.

The Swedes really like to get their money's worth out of their aircraft, and when the Flygvapnet's J 32E Lansen electronic warfare (EW) machines were phased out in 1997, a decision was made to update ten of the fourteen surviving Sk 37s to the "Sk 37E Stoer (Jammer) Viggen" EW configuration. This was actually a fairly substantial upgrade, including:

• A MIL-STD 1553B digital databus and a Global Positioning System (GPS) satellite navigation receiver.
• A new rear cockpit instrument layout for the "electronic warfare officer (EWO)" in the back seat, featuring a flat-panel display system and jammer controls. The back-seater also got his own radio to allow him to communicate independently of the pilot, with a new radio antenna on the spine for the radio. The original back-seat control panel can be restored with a few days' work.
• A G24 radar jammer inherited from the J 32E, fitted in a new nose radome with a "window" that does not attenuate jamming power. The window is marked by a yellow ring on the top of the radome, which provides a recognition feature for the Sk 37E.
• A new Ericsson-SAAB U95 jammer pod.
• Carriage of U22/A defensive jammer pod and a KB chaff-flare dispenser pod, both inherited from phased-out AJS 37 Viggens. The Sk 37E also inherits the RWR from the AJ 37.

Work on the first of the ten "Erik" conversions began in late 1997, with an initial conversion flying in early 1998 and the last conversion performed in 2000. There was some thought to given the Sk 37Es the same two-tone gray color scheme as the JA 37, but though one Erik was painted in this scheme the decision was made that the old splinter camouflage scheme was fine.

The Stoer Viggen's primary mission is EW training, acting as an "electronic aggressor" for Swedish forces in training exercises. It can be fitted with laser reflector pods on the outer wing pylons for scoring purposes. The Sk 37E is capable of being operated as an operational platform, but as a dedicated jammer aircraft tends to be more useful for offense than defense, that aspect of the Erik is downplayed.

In the 21st century, the SAAB 39 rapidly displaced the Viggen from front-line service, but how long it takes for the sun to go down on it completely remains to be seen. About 100 Viggens had been scrapped by 2000, and the type is currently expected to be retired by 2006, but as mentioned the Swedes really like to get their money's worth out of their aircraft, and the Viggen's predecessors had long service lives. The Viggen was an excellent machine when it first flew and it may remain useful, in one role or another, for some time to come.