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GR.4 is the designation for the upgraded GR.1 airframe.  The upgrade is composed of a number of smaller modifications that address a number of issues that have been with the airframe since its inception.   The overall package looks little different from the GR.1 as most of the modifications are internal.

The need for an upgrade to the GR.1 was first thought necessary in 1987/8. The upgrade was to improve the penetration and survivability aspects of the design, but due to defence cuts the upgrade was shelved.

The Gulf War along with other factors again highlighted the need to standardise the configuration of the GR.1 fleet.  The fleet now had many differing standards which led to maintenance and service difficulties.   There were standard airframes, those that had been modified for TIALD, those modified for ALARM and those modified for Sea Eagle amongst others.  Each sub fleet had differing levels of software, Line Replaceable Units(LRUs) and wiring which placed undue strains on the engineers and support logistics units to ensure the rights parts were ordered and fitted to the correct airframe.

Upgrade Program

The GR.4 program will ensure that all airframes modified will be to standard that will cover all the sub fleet needs and introduce the capability and capacity to incorporate any future weapon and defensive systems. The upgrade is to be applied to 142 airframes over the next few years. There is one sub standard within this program which relates to the GR.4A reconnaissance aircraft. The GR.1B designation will become redundant once the GR.4 program has been completed as all GR.4 airframes will become capable of deploying the Sea Eagle missile.

All aircraft are initially delivered to RAF St Athan where preparatory work is undertaken. The airframes are then delivered to British Aerospace at Warton where they are accepted, moved to the production hangar where the rebuild begins.

All major components are removed from the airframe and either stored until they are refitted or sent for overhaul or upgrade. 

The airframes remain at Warton for several months whilst the modifications are incorporated. They then transit to RAF St Athan where they are prepared for Squadron service and dispatched.

Upgrade Process

The stages of conversion are as follows,

1. Airframe and systems are checked to ascertain condition and serviceability, major subsystems removed and stored or sent for rectification and/or modification.
2. The airframe is further stripped in preparation  for modification.
3. All new and modified systems fitted to the airframe.
4. Initial testing of airframe components, while the airframe is still stripped down to allow rectification if necessary.
5. Major subsystems refitted.
6. Initial ground testing.
7. Airframe access panel refitting.
8. Repaint where  necessary, not full airframe.
9. Engine ground runs.
10. Test flight(s).
11. Delivery to St Athan for on ward delivery to front line Squadrons or storage.

The GR.4 upgrade program will be on going for a number of years.  the initial GR.1 to GR.4 program will take until 2002 to complete.  Beyond the initial upgrade there are several further upgrades currently in the wings. The first is projected for March 2000 when an improved software package will be released .  Package 2 is due for release in December 2001 is also a software upgrade.

As with any front line aircraft the fleet will be continually upgraded to enable it to work effectively with other nations Air Forces.

The Upgrade Package

The upgrade consists of a number of individual packages each of which addresses a particular requirement, although all sub packages are thoroughly tested to ensure compatibility with all other systems, hence the need for a number of prototypes.

The prototypes are used to ensure that modifications actually fit within the space available, to ensure the modified components can survive in their proposed location, ie they can survive the environment, the heat, cold, vibration, interference etc. and that there are no compatibility issues.

Weapons System

Two significant changes have been incorporated in the upgrade, these being the introduction of a 1553 data bus which is coupled to a 1760 weapons data bus .  A new weapons control panel has been incorporated which gives the Navigator more control over the stores carried by the aircraft.  A further modification to the system allows the Navigator to perform the weapons pre flight check rather than the ground crew. The system also allows the Navigator to produce live weapons cueing information without the danger of an accidental weapons release.  The GR.4 package also incorporates the necessary wiring and systems to accommodate both existing and new weapons, such as Sea Eagle and Brimstone.  

Video Recording system (VRS)

The GR.1 incorporated a 16mm camera than recorded the radar display, the HUD and the left hand display. The new voice recording system now captures the radar, the HUD, both displays, the FLIR image and all voice and cockpit audio. the new system has some additional capacity built in.  It records onto standard SVHS cassettes.

 Night Vision Goggles (NVG)

Many changes to the cockpit lighting system have been incorporated to ensure the system is fully compatible with night vision goggles.  A new built in test system for the night vision goggle separation system has also been incorporated. 

Forward Looking Infra Red (FLIR)

One of the few noticeable external modifications is the addition of a second fairing under the forward fuselage.  This fairing houses the Forward Looking Infra Red transceiver. The FLIR system basically measures heat radiation and therefore hot objects stand out more than cool objects.  This allows the crew to find targets that may otherwise be camouflaged.

The system can be controlled by either crew member and can be used to provide real time navigation updates.

Flight Planning

The old method of uploading the flight plan into the aircrafts navigation and weapons system has now been replaced. The old system utilised a standard C series magnetic tape that was inserted into the cockpit voice recorder.  the new system utilises a solid state data brick similar to that used on the Harrier.  The new system provide greater reliability due to no moving parts, far faster data transfer as the brick connects directly to the aircraft data bus, far greater capacity and expandability to upload other information directly into the aircraft systems.

Global Positioning System (GPS)

A Global Positioning system has been integrated into the aircrafts navigation and weapons systems.

Heads Up Display (HUD)

A new high definition wide angle heads up display has been fitted which allows a far higher quality of information presentation to be displayed. The new system also allows a far wider range of symbology to be displayed.

Digital Map Generator (DMG)

The digital map generator overlays several pages of information on top of a map of the area in which the aircraft is flying.  This allows the crew to maintain situational awareness with a reduced workload as the system shows such information as  the projected and actual track and high threat locations amongst others.

Laser Inertial Navigation System (LINS)/Ground Proximity Warning System (GPWS)

The GR.4 will be fitted with an BASE/Honeywell 764GT laser inertial navigation system and ground proximity warning system (GPWS).  The ring laser gyro inertial navigation system is the Honeywell 764G which combines an integrated global positioning system (GPS). The ground proximity  warning system was developed by BASE (British Aerospace Systems & Equipment) and is called TERPROMŽ. Further details of this system can be found at