Program Dossier: E-3 Sentry
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The E-3 Sentry Airborne Warning and Control System (AWACS) is an airborne early warning and control (AEW&C) aircraft based on the Boeing 707-320B commercial airliner. The aircraft is powered by four Pratt & Whitney TF33-PW-100A jet engines supplying 20,500 lbf. (91.2 kN) or General Electric CFM56-2 turbofans supplying 24,000 lbf. (106.8 kN) of thrust at sea level each.
The E-3 carries a pulse-doppler mechanically scanned S-band radar in a 30-ft. rotating dome suspended 11 ft. above the fuselage by a pair of struts. This radar is the AN/APY-1 or APY-2, depending on the E-3 variant. The U.S. Air Force (USAF) quotes the radar’s effective range at “more than” 217.2 nmi (402.3 km).
The “rotodome” also contains an identification friend-or-foe (IFF) antenna and antennas for the aircraft’s datalinks. Originally, the E-3 used the Link 4A (TADIL-C) datalink to communicate with fighter aircraft. To facilitate a 360-deg. field of view, the dome is hydraulically rotated at 6 rpm. When not operating the dome rotates at 1/24 of this speed to heat the lubricant and prevent it from congealing.
The E-3 can operate beyond 29,000 ft. (8,840 m). USAF also says the E-3 can operate more than 5,000 nmi (9,260 km) from its base. This estimate goes for aircraft equipped with the TF33. Boeing, for its part, quotes an endurance of six hours at a mission radius of 870 nmi (1,610 km).
The E-3 uses an IBM CC-1 mission computer. Most of the avionics are air cooled, though the radar transmitter has a liquid cooling system. Nine Situation Display Consoles (SDCs) are carried for operators, yielding a typical aircrew of 13. Later variants carry additional consoles and can deploy with more operators.
The aircraft features a refueling slipway above the cockpit to enable in-flight refueling by a boom-type refueler.
The EC-137D was the designation for E-3 prototypes, two of which were built by and retained by Boeing. These were later upgraded to the E-3B standard.
E-3A [Block 10/15]
E-3A aircraft come in two configurations, the “Core” Block 10 and the “Standard” Block 15. Block 15 features the APY-2 radar, an upgraded APY-1 with sea-search capability. Counting the prototypes, the first 25 E-3s are Block 10s. All aircraft produced thereafter carry the APY-2.
E-3B [Block 20]
The E-3B is a modernized E-3 variant upgraded to the Block 20 standard. Block 20 includes five new Situation Display Consoles (SDCs), the IBM CC-2 computer, radio teletype capability and maritime surveillance capability for the APY-1. Five new UHF radios and one HF radio also were fitted, and the UHF radios included feature HAVE QUICK frequency-hopping capability. Block 20 and Block 25 modifications began in 1984.
E-3C [Block 25]
The E-3C is a further upgrade standard similar to the E-3B, but for aircraft with the APY-2.
The E-3D is the E-3 variant procured by the United Kingdom. It features CFM56-2 engines, the APY-2 and the Loral EW-1017 ESM system.
The E-3F is the E-3 variant procured by France. Like the E3-3, it uses the CFM56-2 and carries the APY-2. It was not initially equipped with an ESM system but received one after delivery.
E-3G [Block 40/45]
E-3s receiving Block 40/45 modifications are known as E-3Gs.
The KE-3 is a tanker/cargo derivative of the E-3. It does not feature any elements of the E-3 mission system but has a ventral refueling boom, wingtip drogue pods, a cargo door and a cargo floor. These aircraft are powered by the TF-33.
The RE-3A is a signals intelligence derivative of the KE-3. It features the Tactical Airborne Surveillance System (TASS), a sensor system mounted in two large rectangular fairings on either side of the forward fuselage. These fairings are similar in shape to those seen aboard the USAF RC-135V and RC-135W Rivet Joint. Other small antennas also are present on the underside of the airframe.
The RE-3B is a more advanced derivation of the RE-3B.
The first significant series of E-3 modifications brought aircraft to the Block 30/35 standard. The new Block includes electronic support measures (ESM) capability, the Joint Tactical Information Distribution System (JTIDS) to support the Link 16 datalink, GPS and new computers. These features improve location accuracy for targets passed over Link 16 or Link 11 by a factor of 200.
The main Block 30/35 contract was awarded to Boeing in May 1987. Other upgrades, including GPS capability, were added later. In 1994 Boeing was awarded a $16.8 million contract from NATO and a $127 million contract from the U.S. to procure ESM integration kits for their E-3s. The first Block 30/35 upgrades were completed in October 1995, and the program was finished in 2001.
Radar System Improvement Program (RSIP)
The RSIP program began at the direction of USAF in 1989. It was intended to increase the sensitivity of the E-3 radar system and would bring USAF and NATO APY-1 and APY-2 radars to a common standard. The upgrades improved the electronic countermeasures (ECM) resistance of the system, replaced operators’ consoles, introduced a new radar processor and included new software. NATO joined the program in 1994 as operational test and evaluation of the upgrades was well underway. The UK also joined the program in 1996 when it awarded a contract to Boeing to upgrade all seven of its E-3Ds.
Full rate production began in 1997, with the first kits delivered in 1998. The U.S. installed the kits at Tinker AFB during regularly programmed depot maintenance cycles. NATO kits were installed by Daimler-Benz Aerospace (later EADS and now Airbus) in Germany. In February 2002, France awarded a $133 million contract to Boeing for its own RSIP kits.
Starting in October 1994, the Air Force began a series of E-3 upgrades intended to allow the aircraft to serve to 2025. This predominately included obsolescence management and maintainability improvements
Diminishing manufacturing sources Replacement of Avionics for Global Operations and Navigation (DRAGON)
DRAGON is an E-3 upgrade program jointly pursued by NATO and the USAF. It is intended to replace the E-3’s analog cockpit avionics with a glass cockpit and improve compliance with air traffic management mandates from ICAO and the FAA. This includes ADS-B (Out) capability, a new weather radar, an enhanced ground proximity warning system (EGPWS) and Mode 5 IFF. DRAGON has been pursued concurrently with Block 40/45, and the USAF received the first modified aircraft in January 2017. The upgrades reduce the minimum flight crew from four to three by eliminating the navigator.
The Block 40/45 upgrade brings E-3s to a common E-3G standard and represents an all-around modernization of the E-3 mission system. The upgrades were pursued concurrently with the E-10, the Boeing 767-based replacement for the E-3 and E-8 J-Stars. Block 40/45 testing began in 2006. The upgrade program cost approximately $2.6 billion. It became vitally important after the E-10 program was terminated in 2010.
The upgrade includes the Telephonics AN/UPX-40 IFF system, which provides enhanced clutter rejection over the old system. It also includes new MIDS JTRS Link 16 radios. Most critically, it replaces the computing backend for the aircraft. The flight computer is replaced with a Red Hat Linux-based system and the operator stations are replaced with new Microsoft Windows-based consoles.
Block 40/45 also includes the Internet Protocol Enabled Communications (IPEC) program. IPEC fields an INMARSAT based satellite communications capability on the E-3, enabling full internet connectivity in flight. USAF uses this for IP chat, email and air tasking order and airspace control order dissemination. Aircraft with IPEC carry a rectangular SATCOM antenna just aft of the wing center section.
AWACS Communications Integration Program (ACIP)
ASIP will field a Mobile User Objective System (MUOS) and Second Generation Anti-Jam Tactical UHF Radio for NATO (SATURN) radio capability to the USAF E-3 fleet. The FY23 budget provides $95.2 million for ASIP from FY23 through FY25.
Production and Delivery History
The first E-3s were delivered to the USAF in March 1977. Production terminated in 1992.
Initial operating capability (IOC) for the U.S. E-3 fleet was declared in April 1978. The last aircraft were delivered to the Air Force in 1984. Thirty-four were procured in total. On Sept. 22, 1995, a USAF E-3 77-00354 crashed in Alaska. Of the remaining 33 aircraft, 31 remain in service. Twenty-seven of these are based at Tinker AFB, Oklahoma under Air Combat Command, while the remaining four are based at Kadena AB, Japan, and Elmendorf AFB, Alaska, under Pacific Air Forces.
The FY15 USAF budget request reduced the active inventory from 31 to 24 aircraft, but the inventory was restored in budgets from FY17 through FY19. The see-sawing inventory disrupted the Block 40/45 upgrade program but in FY19 a contract was awarded for the seven remaining Block 30/35 aircraft.
The FY23 Air Force budget proposal decreases modernization funding in view of the Air Force decision to procure a replacement AEW&C aircraft. This includes terminating Block 40/45 funding from FY23 through the FYDP.
The Air Force included $227 million in RDT&E funds for an E-3 replacement in its FY23 budget request. The funds will be used to procure a prototype, which the Air Force says will be delivered in 2027. Another prototype would be bought in FY24 with a production decision in FY25. The Air Force formally selected the Boeing E-7A Wedgetail on April 26, 2022. All prior sales of E-7s have been conducted through Direct Commercial Sales rather than Foreign Military Sales – meaning different intellectual property, financial and other regulations would apply to a prospective USAF acquisition.
The Wedgetail is a Boeing 737-700 carrying Northrop Grumman’s L-band Multi-role Electronically Scanned Array (MESA). This electronically scanned radar is a generational leap over the APY-1/2 capability and is fully mature, having served with the Royal Australian Air Force for over ten years.
This lengthy development phase is interesting in light of the maturity of the E-7 capability and of new Air Force plans to dramatically cut the E-3 fleet in the near term. The FY23 budget request envisions divestment of 15 of the Air Force’s 31 E-3s in FY23 and FY24. The Air Force previously intended to keep its 33 E-3s in service until 2035. It is unclear if Congress will authorize E-3 divestment since it will generate a capability gap spanning the rest of the decade, if not longer. Rep. Tom Cole (R-Okla.), for example, said at a May 13, 2023, House Appropriations defense subcommittee hearing that the E-3 retirement plan was a “big risk” and one that “is not wise to take.” For more on the replacement plan, see Aviation Week’s program profile on the E-7 .
Also noteworthy is a lone ex-RAF E-3D bought by the U.S. Navy in June 2021. This E-3D will have its mission equipment removed and will be used by the Navy as a trainer for E-6B Mercury flight crews. Procuring a dedicated trainer will increase the operational availability of the E-6B fleet by reducing the requirement for these aircraft to fly training sorties. For more information on the E-3D acquisition and the E-6 fleet, see Aviation Week’s program profile on the E-6.
The North Atlantic Treaty Organization (NATO) decided in December 1978 to acquire a joint AEW&C capability. It opted to procure 18 E-3As. The first was delivered in January 1982, and all were delivered in E-3A Block 15 configuration. One of these was lost in an accident in 1995 and another was parted out for spares in 2015. One each was retired in 2017 and 2018, leaving 14 in service as of June 2022.
In October 1980, NATO formed its Airborne Early Warning and Control Force. The command controls NATO’s E-3 fleet and controlled the RAF E-3D force before its retirement. The aircraft fly out of forward operating sites in Greece, Italy, Norway and Turkey. NATO’s E-3s began flight operations in 1982.
The Force is managed by a group of sixteen NATO countries comprising the NAEW&C Programme Management Organization (NAPMO). As of 2022, the NAPMO members are Belgium, the Czech Republic, Denmark, Germany, Greece, Hungary, Italy, Luxembourg, the Netherlands, Norway, Poland, Portugal, Romania, Spain, Turkey and the United States. The UK was never a full NAPMO member but contributed its E-3Ds to the force. France is a NAPMO observer, and coordinates to maintain the interoperability of its E-3 fleet.
In December 2019, NAPMO signed a $1 billion contract with Boeing for a Final Lifetime Extension Program to bring the service life of the NAEW&C force to 2035.
In 1981, Saudi Arabia signed a contract to acquire five E-3As and six KE-3 aerial refueling aircraft. The contract included an option for an additional four KE-3s, which was exercised in 1984. All aircraft were delivered by the end of 1987. Of the KE-3s, four were converted to RE-3As. Three of these later received the more extensive KE-3B upgrade. Another KE-3 was retired, leaving only five of these in service.
Starting in August 2001, Boeing applied mission computer upgrades to the Saudi E-3 fleet. The $60 million contract included related hardware and software changes and was completed in 2003. In September 2007, the Kingdom contracted for the installation of JTIDS terminals. The same year, it requested access to the RSIP upgrade – a contract was awarded in 2008.
From 2009, the fleet began receiving new MIDS/LVT sets, new crypto equipment and new radios. Finally, in 2019, a Foreign Military Sales (FMS) contract was awarded for UPX-40 sets for the fleet. While the Royal Saudi Air Force has not brought its fleet to the Block 40/45 standard outright, its aircraft now have many of its capabilities.
In 1986, the UK released a solicitation for proposals for an AEW&C aircraft to fill the gap left by the imminent cancellation of the Nimrod AEW3 program. AEW3 would have been an AEW&C derivative of the Nimrod maritime patrol aircraft, with air search radars mounted to the nose and tail. By September 1986 the E-3 was the only remaining alternative to the Nimrod, and it was selected in December. Six were to be procured for the Royal Air Force (RAF), with the CFM56-2 engines. An option for a seventh was exercised in late 1987. The first aircraft was delivered in March 1991, with deliveries complete in May 1992. Britain’s E-3s were equipped with probes to support the probe and drogue refueling system used by its air force and with new radio equipment.
The UK’s 2021 Integrated Defence Review included a decision to retire the E-3D force ahead of the incoming Boeing E-7A Wedgetail, its replacement. Retirement of the aircraft by the end of 2021 created a capability gap, as the E-7 will not enter RAF service until 2023.
France ordered three E-3Fs in February 1987 in a similar configuration to the British aircraft. This includes the refueling probes and radio upgrades. Later that year the French government exercised an option for a fourth aircraft. The aircraft were delivered from May 1991 to February 1992.
In June 2022, only four E-3s are still operational. These four all received Block 40/45 upgrades starting in 2014 under a 2010 FMS contract, while the three remaining aircraft were retired.
Chile has signed a contract with the UK to procure three retired E-3Ds to replace the Chilean air force’s lone IAI Phalcon (known in Chile as the Cóndor). The Phalcon is a modified Boeing 707-385C. The E-3Ds are likely to enter service by the end of 2022.
Prepared by Sterling Richmond, [email protected]