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Sunday, July 1, 2001

Military Upgrades: How the Royal Navy Advanced Its AEW

We look at the British Royal Navy's efforts to upgrade its airborne early warning. We also gain a preview of the service's future plans in this area.

George Marsh

AFTER BEING STUNG BADLY during the 1982 Falklands conflict, the British Royal Navy had 10 of its Sea King HAS Mk2 helicopters initially retrofitted with Thorn-EMI (later Racal and now Thales Avionics) Searchwater radars to provide airborne early warning (AEW) of attacks against its ships by sea-skimming missiles. The AEW response, rapidly contrived by the Royal Navy and British industry, was effective. And with some 13 airframes eventually modified to carry the distinctive bulbous swiveling radome and house an interior sensor operator workstation, the Sea King AEW Mk2 remained in service substantially unaltered. Until recently.

Currently, all 13 AEW Mk2 aircraft are undergoing a mission system upgrade (MSU), which will give them a much-enhanced AEW capability. Prime contractor Thales Avionics is responsible for fitting the Sea Kings with new navaids and radar, the Link 16 data link, and updated crew accommodations.

The resulting Sea King AEW Mk7 should enter service in March 2002. Thales has declared that the project is still on schedule to meet the December 2001 service entry date.

Recently providing Avionics Magazine with further details of the program is senior marketing manager, airborne systems, Mike Attfield. He claims the AEW Mk7 (also colloquially known as SKW or Whisky) upgrade will provide a vastly improved mission capability with, in particular, a radar that is comparable with the world's best.  

Mission System

The AEW mission system, according to Attfield, integrates the powerful new Searchwater 2000 pulse-Doppler radar with the following:

  • A MkXII IFF (identification friend or foe) from BAE Systems/Hazeltine;

  • Link 16 data link communications from Rockwell Collins (hardware) and Logica (software);

  • A Litton inertial navigation/Global Positioning System (INS/GPS) nav system;

  • And a dual-operator console designed by the Royal Navy, working with prime contractor Thales Avionics.

At the heart of the system is the new Searchwater 2000 radar, substantially re-engineered from the earlier Searchwater used on the AEW Mk2 Sea King. It differs as well from another recent Searchwater variant, developed for the Royal Air Force's extensively reworked Nimrod MR4A maritime reconnaissance aircraft. For example, it has been optimized to detect and track small, fast-moving targets against a sea (as distinct from a land) background.  

A Flexible Response

Indeed, the AEW Mk7's long-range look-up/look-down system also can detect a wide range of small airborne targets over both land and sea. Moreover, while primarily intended to protect fleets from possible surprise attack from the air, the radar still retains the Searchwater's original maritime reconnaissance capabilities, including surface target classification. This will ensure a flexible and capable response to fast surface craft, as well as to missiles--which is important at a time when coastal operations are just as likely as oceanic ones.

To provide the required multimode capability, the radar has been extensively redesigned for operation in X-band and pulse Doppler mode. A Raytheon transmitter and antenna are complemented by a new electronic antenna drive system, which is faster and more efficient than the previous hydraulic system.

Radar modes available include:

  • Air-to-air (look-up and look-down);

  • Moving target indicator (MTI);

  • Maritime surveillance for anti-submarine and anti-surface ship warfare (ASW/ASuW) operations in littoral zones or open water;

  • Navigation and ground mapping;

  • Target classification; and

  • Weather and beacon.

During sector scanning, the radar can provide a combined, pulse Doppler/pulse envelope (PD/PE) mode, PD spotlight, PD modes and a passive (listen) mode. Multibar scanning provides multiple raid detection capability, while PD/PE interlacing enables targets to be detected at maximum range, then tracked through background clutter. High pulse Doppler performance together with littoral surveillance mode allows targets to be tracked over land and through coastal waters. Searchwater radars are noted for their ability to detect small targets even in severe land or sea clutter.

The AEW Mk7 radome is the same size and configuration as on the AEW Mk2. It houses the main radar antenna, along with its drive servos. The antenna swivels 90º between deployed and stowed positions. Other radar elements are housed in a dedicated electrical rack in the main cabin, forward of the observer console. The receiver/exciter resides on the top three shelves. Signal and data processors are on another shelf, and the amplifier electronic control (AEC) unit is on still another. On the bottom shelf is a joint tactical information distribution system (JTIDS) host processor (JHP).

A twin sensor operator console in the main cabin has two large, 20-inch (51-cm) high resolution, color flat-panel displays and four interactive touch-screen control panels based on established Racal human-machine interface (HMI) technology. Each main display provides a clutter-free radar picture with pop-up data windows. Air and sea picture symbology can be overlaid on geographical features. On-screen menus are carefully designed to ease the operator's task. The interactive control panels have system-management features and mini-displays for target profiles, raid assessment information, radar coverage displays, and text messages.  

An Intuitive System

The operator interface is uniquely developed because it was designed largely by the Royal Navy airborne sensor operators themselves, working closely with Thales. This level of customer involvement has resulted in a highly intuitive system, said to rival that of other advanced AEW powerhouses such as the Boeing E-3 Sentry.

Originally, the console was to have had cathode ray tube- (CRT)-based main displays. But the emergence of a sufficiently large and clear flat-panel product during the program led to its selection instead.

Royal Navy observers will be able to use drag-and-drop graphics to set up a radar scanning program before each flight. Despite the added complexity of multiple modes, such preprogramming will be much faster than was possible on the AEW Mk2 aircraft. A mere three keystrokes will access any function. Working together, the two observers will be able to track some 600 contacts at a time, whereas dealing with more than a dozen on the Mk2 system proved a challenge.  

'What the Hell Is Going On?'

The AEW Mk7 surpasses the Mk2 in other ways. Data link capability, notably lacking in the Mk2, is integral to the new mission system. The Link 16/JTIDS system from Rockwell Collins/Logica, along with the superior operator HMI, makes exchanging data--radar situation displays, for instance, plus command and control functions--easy.

When, for example, intercept orders have to be passed to combatants, operators need to make just a few keystrokes to prepare and transmit a message. Rather than creating a new order, a couple of keystrokes can cancel a message, as well.

One feature likely to be particularly popular in the fog of war is a weapon target fighter global overview (WTFGO) button. Using this "what the hell's going on?" feature, an operator can summon an immediate tactical picture, based on his own and outside data.

High accuracy in reporting one's own position and exchanging target data is ensured by a new integrated navigation system. The Litton inertial/GPS nav system, incorporating ring laser gyro and embedded GPS, also provides radar stabilization. An integrated IFF system modes 1-4 and C from BAE Systems (GEC Marconi)/Hazeltine provides identification friend or foe.  


Thales has tested its radar extensively, including vibration testing. Isolation performance is critical in a pulse Doppler system, from which operators rely on fraction-of-a-degree phase shifts to reveal the presence of tiny targets travelling supersonically in land and sea clutter. The radar also has been undergoing flight trials and was scheduled for military aircraft release by this summer.

Other elements of the mission system have been subject to equivalent testing, both individually and within the mission system upgrade. The Defence and Research Agency (DERA) conducted the ground phase of an overall assessment of the MSU for the Royal Navy. And airframe manufacturer GKN Westland performed ground-based trials of the full MSU installation on the first airframe prior to flight testing.

Inevitably, in a project of this complexity, a number of issues will arise. The AEW Mk7's radar transmitter, for instance, required further attention. With the various fixes now implemented or identified, the system now is in the midst of several months of flight testing. Among the chief objectives for this activity has been to gather air, sea and land target data in both PD and PE radar modes and to further check the coherency of the high-power Doppler radar system in the genuine vibration environment of a Sea King helicopter.  

Other Modernization Efforts

An original program based on a single test aircraft was superseded and expanded in scope. To reduce timescale and risk, trials of the MSU now are combined with those of another Sea King mission upgrade, an enhanced communications system (ECS). This brings a second aircraft into the combined flight test effort. Also under flight evaluation is an airborne video recording system that is part of the AEW7 upgrade, plus active noise reduction and an airframe modification.

The first AEW Mk2 aircraft to be upgraded has been modified with full mission system by GKN Westland Helicopters. As airframe authority and program subcontractor, it integrated the equipment into the airframe at its Weston-super-Mare (Somerset, UK) facility. Trials, which started in August 2000, are expected to last into spring 2001, after which the first two equipped helicopters will be reassigned to aircrew training prior to service entry, planned for December. The Mk7 was envisaged as a three-crew aircraft, with single pilot and two sensor operators in the rear. One of the operators will be cross-trained to act as a second pilot, if necessary.

DERA Boscombe Down is conducting flight testing at RAF Saint Mawgan for instrumented trials over both land and sea, and at a site in northern England for data link evaluation. DERA will then carry out the final phase, the full military aircraft release trials, in late fall of this year.  

Virtues of Jointness

According to Attfield, the close involvement of the customer in the MSU's development resulted in a conference of all involved parties to clear the equipment installation on the first aircraft as ready and safe to fly. The joint evaluation team brought together prime contractor Thales, GKN Westland and other major sub contractors along with the Royal Navy. This allowed every aspect of the system to be reviewed jointly, with actions and acceptance being decided on the spot--rather than the more usual and lengthy procedure of each organization reviewing and reporting separately.

"This proved a much faster process," comments Attfield. Also, we have an unusually close-knot relationship with our MoD customer on this project, and it's paying off."

A joint project team has been formed to get the equipment onto production aircraft. Thales Avionics chairs meetings of the integrated product embodiment team (IPET) and leads the test activities, while GKN Westland Helicopters leads in the equipment installation. The joint team also will establish longer-term customer support and post-design service requirements and develop a phased plan for future enhancements such as knowledge-based systems and new electronic support measures.

Beyond the Sea King

In developing the AEWMk7 mission system, the Royal Navy has been thinking beyond its Sea King platforms. Elements of the system may transfer into the Ministry of Defence's future organic airborne early warning (FOAEW) system, which the agency asked Thales to study soon after it awarded the Mk7 contract. In the long term, the British Royal Navy plans to supersede its present three Invincible Class carriers, bearing helicopters and Harriers, with two carrier vessel future (CVF) ships.

Given the new carriers, the maritime anti-air warfare platform need not be a helicopter. It could be a fixed-wing aircraft, like the Northrop Grumman E-2 Hawkeye, an aerostat (airship), or a tilt-rotor like the Bell Boeing V-22 Osprey. If itwereto be a helicopter, the aircraft would need to offer far superior performance to the Sea King. The RN's present Agusta-Westland EH-101 Merlin, augmented with stub wings, has been suggested as an affordable option.

Whatever the final choice, a larger airframe will accommodate a more powerful radar sensor, probably utilizing active phased array technology and with synthetic aperture and moving target indication capabilities. A greater number of systems operators may be placed on-board the FOAEW, to deal with the aircraft's extended roles and increased data input. Knowledge-based computer systems will help them make rapid assessments and decisions, while other computers will provide effective sensor fusion and a high level of situational awareness.

Although requirements have yet to be defined, the Royal Navy will want FOAEW to have the following capabilities:

  • A highly developed ability to detect and track both high- and low-flying offensive aircraft and missiles over land and sea;

  • Sea, land and airspace surveillance;

  • Attack coordination;

  • Tactical air control; and

  • Data link to exchange target and command and control information with other assets, to contribute fully to the future digital battle space.

Thales has completed a first-phase study of the FOAEW program. At the time of writing, contracts for the second phase--to identify systems integration risks--have been awarded to Thales and the BAE Systems/Northrop Grumman team. Phase two is to be completed by the end of this year; then, in January 2002, the program is to advance to the systems demonstration phase, involving prototyping and a new version of data processing. An initial down-select in March 2003 would then be followed by a go-ahead for the final submission three years later. Entry into service is not expected before 2012.

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