Structure and Systems

The basic E-3 aircraft is a militarized version of the Boeing 707-320B airframe. It is distinguished by the addition of a large, rotating radome towards the rear of the fuselage. The dome is 30 feet (9.1 meters) in diameter, six feet (1.8 meters) thick, and is held 11 feet (3.33 meters) above the fuselage by two struts.

There are six versions of the E-3, each with a different avionics configuration. These are the USAF E-3B and E-3C, the NATO E-3A, the Saudi Arabian E-3A, the Royal Air Force E-3D and the French Air Force E-3F. In addition, two different types of engine are in use.

Most E-3s carry a flight crew of 4 and up to 13 mission specialists. The USAF E-3C increases this to 17 mission specialists.

Dimensions

Wing span:44.42m
Length:46.61m
Height:12.6m
Wing Area:283.4m²
Empty Weight:73480kg approx.
Loaded Weight:147400kg
Max T/O Weight:151955kg

The rotodome is 9.14m in diameter, and 1.82m thick in the centre.

Performance

Maximum speed:853 km/hr
Operating speed:~563 km/hr
Service ceiling:over 8850m
Endurance:11 hr+
Range:>9250 km

Powerplant

USAF and NATO E-3s have four Pratt and Whitney TF33 turbofan engines, each of which is rated at 95.2 kN. Saudi, British and French aircraft have the GE/Snecma CFM-56 turbofan, which is rated at 108.9 kN and is considerably more fuel-efficient.

Fuel capacity is around the 70 tonne mark. All E-3s have air-refuelling capability. The RAF and French aircraft can be refuelled by both probe-and-drogue and flying boom methods, but the USAF, NATO and Saudi aircraft are only compatible with the latter.

Avionics

The E-3 is one of those aircraft whose avionics are much more important than the airframe and engines. A large number of systems are installed, and it is quite difficult to work out exactly what is fitted to the different E-3 variants.

E-3 console

Most E-3s have nine multi-purpose consoles to control all the mission equipment, but the USAF E-3C variant has three extra consoles and other electronic enhancements not fitted to other aircraft. Various security-sensitive equipment is not fitted to the Saudi E-3As.

NATO E-3 internal arrangement

Radar

The E-3's Westinghouse AN/APY-1/2 radar has five operational modes plus built-in test/fault-finding and on-board simulation. The liquid-coooled planar-array radar antenna and back-to-back AN/APX-103 Mk 10/12 IFF are fixed inside the rotodome, which rotates at 6rpm when in use, and 1/3rd rpm at other times.

The radar simultaneously transmits low-PRF pulsed-radar, and high-PRF pulse-Doppler. The former is used to detect long-range targets, and the latter to detect low- and high-flying targets out to the radar horizon. All targets detected by the PD element have their heights measured. The APY-1 has small transmitter side lobes which improve target detection against a background of clutter from land or sea, and decrease ECM vulnerability. Nominal radar horizon at 8840m is about 360km.

The APY-1 can also operate in passive mode, not transmitting but continuing to receive electronic transmissions from radars, etc. A maritime surveillance mode is a modification, and uses a very short pulse to reduce sea clutter, and bringing the moving target indicator limit speed down from its 145km threshold to zero, thus presenting stationary or slow-moving targets for display.

From 1997 an improved IFF system was being installed in USAF E-3s.

Also from 1997 the APY-1/2 radars in NATO, RAF and USAF aircraft began to be upgraded under a Radar System Improvement Programme. The RSIP increases the sensitivity of the radar and allows it to detect and track smaller targets over longer ranges in the pulse-Doppler mode. The RSIP also includes a new radar computer and control maintenance panel, and electrical and mechanical hardware. The NATO RSIP kits were installed by DASA, and the RAF ones by British Aerospace. USAF E-3s will have the RSIP upgrade by FY2005. The French AF E-3Fs are also to receive the RSIP upgrade.

RSIP improved the E-3's radar by increasing the sensitivity of the pulse-Doppler radar so the aircraft can detect and track smaller targets over a longer range. It also improves the radar's ECCM capability.

RAF E-3D radars have Maritime Scan-to-Scan Capability (MSSC) installed.

Data Processing

The Data Processing Functional Group (DPFG) is the core of the E-3's data processing system. This executes mission computer programs, maintenance checks and utility programs. In 1981 the DPFG used the IBM 4Pi CC-1 real-time computer, which was capable of semi-automatic reconfiguration. The CC-1 had a processing speed of 740K operations per second.

The USAF Block 30/35 upgrade involves the installation of the CC-2E central computer. This computer has also been fitted to NATO E-3As.

The Airborne Operational Computer Program includes the DPFG, as well as the separate computers which handle the aircraft navigation subsystems and the mission radar data correlator, using data inputs from all onboard avionics.

Under the NATO mid-term modernisation program, Boeing is to upgrade the NATO E-3 fleet. The computing enhancements include installing flat-panel situation displays with a Windows-like environment. The mission computing system will be replaced by an open-system architecture, which will allow commercial hardware and software to be added in a cost-effective way.

Communications

The E-3 has a number of communication systems. The most important of these are the Tactical Data Information Link (TADIL) and the Joint Tactical Information Distribution System (JTIDS). TADIL-A (Link 11A) is used to exchange tactical data with other E-3s, air or ground command posts, and ships. In a radar-jamming environment, TADIL-A users can locate the jamming source by exchanging bearings for co-operative triangulation.

JTIDS (TADIL-J or Link 16) is a secure communications system used to datalink information between air and ground units. The NATO Block 1 upgrade included JTIDS/Link 16. The USAF Block 30/35 upgrade includes the installation of Class 2H JTIDS. The Saudi E-3As are not fitted with JTIDS.

Also available are UHF and HF narrow-band secure voice, UHF wide-band secure voice and UHF and VHF clear voice channels.

Have Quick anti-jam UHF radio equipment has been fitted in NATO and USAF E-3s.

From 1997 an improved HF radio system was being installed in USAF aircraft.

In July 2004 Thales was awarded a contract by Boeing to upgrade the communications management and intercom systems for 16 NATO E-3As, and for two mission simulators. Thales also won a contract from the NATO AEW&C Programme Management Agency for workshop maintenance of communications equipment over a ten-year period.

Under the NATO mid-term modernisation program, Boeing will upgrade the NATO E-3 fleet. The communications enhancements include the installation of digital systems and the integration of satellite communications into the mission system. Also, broad-spectrum VHF radios will be fitted. In November 2004 EADS was awarded a contract for mission computers and Multi-Sensor Integration (MSI) computers as part of the upgrade. The MSI software permits the automatic identification and tracking of targets as well as the generation of target flight paths by integrating the reconnaissance data available to the E-3. The first upgraded aircraft is due to become operational in 2006.

In October 2004 the AWACS Systems Program Office took part in a test of an Identification Friend or Foe (IFF) Mode 5 interrogator at Patuxent River. The US Air Force hopes to begin installing Mode 5 interrogators on Sentries in FY 2008, replacing the existing Mode 4 equipment.

In July 2005 Boeing started to install enhanced satellite communications on the first USAF E-3. This is scheduled to be completed in January 2006. The entire fleet will have been upgraded by the end of 2010.

Electronic Support Measures

USAF and NATO E-3s are being fitted with the AN/AYR-1 passive sensor system, which can locate fighter radars 550 km away. This takes the form of a 3.96m canoe-shaped bulge on each side of the aircraft's forward fuselage, supplemented by pairs of smaller bulges on the nose and tail. The first NATO aircraft fitted with this equipment, LX-N90442, returned to Geilenkirchen in October 1991.

In October 1995 the first USAF aircraft was fitted with the AYR-1 as part of the Block 30/35 upgrade. The remaining aircraft are being retrofitted at Oklahoma City ALC by 2001. Aircraft weight is increased by 862kg. French E-3Fs will also receive the equipment.

The RAF's E-3Ds were specified with Loral Yellowgate ESM which performs a similar function. The sensors for this system are housed in wingtip pods. In April 1999 Racal-Thorn Defence was awarded a contract worth about £5m to upgrade Yellowgate. These improvements will enhance the aircrew's threat warning and surveillance data, as well as reducing the system's weight and increasing its reliability.

French Air Force E-3Fs are also fitted with ESM equipment.

Navigation Systems

GPS/INS is installed on USAF aircraft as part of the Block 30/35 upgrade, and has also been installed on RAF E-3Ds.

Under the NATO mid-term modernisation program, Boeing will install GPS into the E-3 fleet.

Other Systems

In July 2005 Boeing started to install air traffic management upgrades on the first USAF E-3. The Global Air Traffic Management System permits AWACS to operate efficiently in congested airspace worldwide, especially in Europe and the US East coast corridor, by allowing the AWACS to fly in closer proximity to other aircraft. Additional enhancements include a traffic collision avoidance system, which sounds an alert and provides a message climb or descend to the AWACS flight crew in order to prevent a collision.

Retrofit of the first aircraft is scheduled to be completed in January 2006. The entire fleet will have been upgraded by the end of 2010.

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© David Hastings