Boeing 707 негізіндегі әуе шабуылының ерте ескерту және басқару ұшағы

Airborne early warning and control aircraft based on Boeing 707 airframe

The Boeing E 3 Sentry is an American airborne early warning and control (AEW&C) aircraft developed by Boeing. E 3s are commonly known as AWACS (Airborne Warning and Control System). Derived from the Boeing 707 airliner, it provides all weather surveillance, command, control, and communications, and is used by the United States Air Force, NATO, French Air and Space Force, Royal Saudi Air Force and Chilean Air Force. The E 3 has a distinctive rotating radar dome (rotodome) above the fuselage. Production ended in 1992 after 68 aircraft had been built. In the mid 1960s, the U. S. Air Force (USAF) was seeking an aircraft to replace its piston engined Lockheed EC 121 Warning Star, which had been in service for over a decade. After issuing preliminary development contracts to three companies, the USAF picked Boeing to construct two airframes to test Westinghouse Electric and Hughes's competing radars. Both radars used pulse Doppler technology, with Westinghouse's design emerging as the contract winner. Testing on the first production E 3 began in October 1975. The first USAF E 3 was delivered in March 1977, and during the next seven years, a total of 34 aircraft were manufactured. E 3s were also purchased by NATO (18), the United Kingdom (7), France (4) and Saudi Arabia (5). In 1991, when the last aircraft had been delivered, E 3s participated in the Persian Gulf War, playing a crucial role of directing coalition aircraft against Iraqi forces. The aircraft was also the last of the Boeing 707 derivatives after 34 years of continuous production. The aircraft's capabilities have been maintained and enhanced through numerous upgrades. In 1996, Westinghouse Electric's Defense & Electronic Systems division was acquired by Northrop Corporation, before being renamed Northrop Grumman Mission Systems, which currently supports the E 3's radar. In April 2022, the U. S. Air Force announced that the Boeing E 7 is to replace the E 3 beginning in 2027.

In 1963, the USAF asked for proposals for an Airborne Warning and Control System (AWACS) to replace its EC 121 Warning Stars, which had served in the airborne early warning role for over a decade. The new aircraft would take advantage of improvements in radar technology and computer aided radar data analysis and data reduction. These developments allowed airborne radars to "look down", i. e. to detect the movement of low flying aircraft, and discriminate, even over land, target aircraft's movements; previously this had been impossible due to the inability to discriminate an aircraft's track from ground clutter. Contracts were issued to Boeing, Douglas, and Lockheed, the latter being eliminated in July 1966. In 1967, a parallel program was put into place to develop the radar, with Westinghouse Electric Corporation and Hughes Aircraft being asked to compete in producing the radar system. In 1968, it was referred to as Overland Radar Technology (ORT) during development tests on the modified EC 121Q. The Westinghouse radar antenna was going to be used by whichever company won the radar competition since Westinghouse had pioneered the design of high power radio frequency (RF) phase shifters, which are used to both focus the RF into a pencil beam and scan electronically for altitude determination. Boeing initially proposed a purpose built aircraft, but tests indicated it would not outperform the already operational 707, so the latter was chosen instead. To increase endurance, this design was to be powered by eight General Electric TF34s. It would carry its radar in a rotating dome mounted at the top of a forward swept tail, above the fuselage. Boeing was selected ahead of McDonnell Douglas's DC 8 based proposal in July 1970. Initial orders were placed for two aircraft, designated EC 137D, as test beds to evaluate the two competing radars. As the test beds did not need the same 14 hour endurance demanded of the production aircraft, the EC 137s retained the Pratt & Whitney JT3D commercial engines, and a later reduction in the endurance requirement led to retention of the JT3D engines in production. The first EC 137 made its maiden flight on 9 February 1972, with the fly off between the two radars taking place from March to July of that year. Hughes' radar was initially thought to be a certain winner due to its related development of the APG 63 radar for the new F 15 Eagle. The Westinghouse radar used a pipelined fast Fourier transform (FFT) to digitally resolve 128 Doppler frequencies, while Hughes's radars used analog filters based on the design for the F 15. Westinghouse's engineering team won this competition by using a programmable 18 bit computer whose software could be modified before each mission. This computer was the AN/AYK 8 design from the B 57G program, and designated AYK 8 EP1 for its much expanded memory. This radar also multiplexed a beyond the horizon (BTH) pulse mode that could complement the pulse Doppler radar mode. This proved to be beneficial especially when the BTH mode is used to detect ships at sea when the radar beam is directed below the horizon.

Approval was given on 26 January 1973 for the full scale development of the AWACS system. To allow further development of the aircraft's systems, orders were placed for three preproduction aircraft, the first of which performed its maiden flight in February 1975. IBM and Hazeltine were selected to develop the mission computer and display system. The IBM computer was designated 4PI, and the software was written in JOVIAL. A Semi Automatic Ground Environment (SAGE) or back up interceptor control (BUIC) operator would immediately be at home with the track displays and tabular displays, but differences in symbology would create compatibility problems in tactical ground radar systems in Iceland, mainland Europe, and South Korea over Link 11 (TADIL A). In 1977, Iran placed an order for ten E 3s, however this order was cancelled following the Iranian Revolution. Engineering, test and evaluation began on the first E 3 Sentry in October 1975. Between 1977 and 1992, a total of 68 E 3s were built.

Because the Boeing 707 is no longer in production, the E 3 mission package has been fitted into the Boeing E 767 for the Japan Air Self Defense Forces. The E 10 MC2A was intended to replace USAF E 3s—along with the RC 135 and the E 8 Joint STARS, but the program was canceled by the Department of Defense. NATO intends to extend the operational status of its AWACS until 2035 when it is due to be replaced by the Alliance Future Surveillance and Control (AFSC) program. The Royal Air Force (RAF) chose to limit investment in its E 3D fleet in the early 2000s, diverting Sentry upgrade funds to a replacement program. On 22 March 2019, the UK Defence Secretary announced a $1.98 billion (~$ in ) contract to purchase five E 7 Wedgetails. The U. S. Air Force intends to retire 15 of its 31 E 3s and acquire the E 7. On 31 March 2023, the USAF retired an E 3 from service for the first time.

The E 3 Sentry's airframe is a modified Boeing 707 320B Advanced model. Modifications include a rotating radar dome (rotodome), uprated hydraulics from 241 to 345 bar (3500–5000 PSI) to drive the rotodome, single point ground refueling, air refueling, and a bail out tunnel or chute. A second bail out chute was deleted to cut mounting costs. USAF and NATO E 3s have an unrefueled range of or 8 hours of flying. The newer E 3 versions bought by France, Saudi Arabia, and the UK are equipped with newer CFM56 2 turbofan engines, and these can fly for about 11 hours or more than The Sentry's range and on station time can be increased through air to air refueling and the crews can work in shifts by the use of an on board crew rest and meals area. The aircraft are equipped with one toilet in the rear, and a urinal behind the cockpit. Saudi E 3s were delivered with an additional toilet in the rear.

Between 1987 and 2001, USAF E 3s were upgraded under the "Block 30/35 Modification Program". Enhancements included:
The installation of ESM and an electronic surveillance capability, for both active and passive means of detection. Installation of the Joint Tactical Information Distribution System (JTIDS), which provides rapid and secure communication for transmitting information, including target positions and identification data, to other friendly platforms. Global Positioning System (GPS) capability was added. Onboard computers were overhauled to accommodate JTIDS, Link 16, the new ESM systems and to allow for future enhancements.

The Radar System Improvement Program (RSIP) was a joint US/NATO development program. Saudi Arabia began RSIP upgrades in 2013; the first aircraft being upgraded by Boeing in Seattle with the four remaining aircraft upgraded in Riyadh between 2014 and 2016.

Between 2000 and 2008 NATO upgraded its E 3s to Mid Term Program (MTP) standard. This involved technical upgrades and a total multi sensor systems integration

In 2009, the USAF, in cooperation with NATO, entered into a major flight deck avionics modernization program in order to maintain compliance with worldwide airspace mandates. The program, called DRAGON (for DMS Replacement of Avionics for Global Operation and Navigation), was awarded to Boeing and Rockwell Collins in 2010. Drawing on their Flight2 flight management system (FMS), almost all the avionics were replaced with more modern digital equipment from Rockwell Collins. Main upgrades include a Digital Audio Distribution System, Mode 5/ADS B transponder, Inmarsat and VDL datalinks, and a terrain awareness and warning system (TAWS). The centerpiece flight deck hardware consists of five 6x8 color graphics displays and two color CDUs. DRAGON laid the foundation for subsequent upgrades including GPS M Code, Iridium ATC, and Autopilot. USAF DRAGON Production began in 2018.

In 2014 the USAF began upgrading block 30/35 E 3B/Cs into block 40/45 E 3Gs. This upgrade replaces the main flight computer with a Red Hat Linux based system, as well as replacing the DOS 2.0 like operating system with a Windows 95 like system on the operator workstations. In 2016, a three week long cybersecurity vulnerability test revealed that the 40/45 block and its supporting ground equipment were vulnerable to cyber threats, and were thus deemed "not survivable." This caused a delay of approximately two years. Twenty four E 3s are projected to complete this upgrade to 40/45 by the end of fiscal year 2020, while seven aircraft will be retired to save upgrade costs and harvest out of production components.

NATO intends to extend the operational status of its AWACS until 2035 by significantly upgrading fourteen aircraft in the Final Lifetime Extension Program (FLEP) between 2019 and 2026.

In March 1977 the 552nd Airborne Warning and Control Wing received the first E 3 aircraft at Tinker AFB, Oklahoma. The USAF has a total of thirty E 3s in active service. Twenty six are stationed at Tinker AFB and belong to the Air Combat Command (ACC). Four are assigned to the Pacific Air Forces (PACAF) and stationed at Kadena AB, Okinawa and Elmendorf AFB, Alaska. One aircraft (TS 3) was assigned to Boeing for testing and development (retired/scrapped June 2012). The data collection capability of the E 3 radar and computer subsystems allowed an entire air war to be recorded for the first time. In addition to providing senior leadership with time critical information on the actions of enemy forces, E 3 controllers assisted in 38 of the 41 air to air kills recorded during the conflict. Over 1,000 aircraft operating from bases in Germany and Italy took part in the air campaign which was intended to destroy Yugoslav air defenses and high value targets such as the bridges across the Danube river, factories, power stations, telecommunications facilities, and military installations. On 18 November 2015, an E 3G was deployed to the Middle East to begin flying combat missions in support of Operation Inherent Resolve against ISIL, marking the first combat deployment of the upgraded Block 40/45 aircraft.

In February 1987 the UK and France ordered E 3 aircraft in a joint project which saw deliveries start in 1991. The British requirement arose due to the cancellation of the BAE Nimrod AEW3 project. UK E 3Ds formed the E 3D Component of the NATO Airborne Early Warning and Control Force (NAEWCF), receiving much of their tasking directly from NATO. However, RAF E 3Ds remain UK crewed and capable of independent, national tasking. This has been done on numerous occasions, notably when E 3Ds were committed to operations over Afghanistan in 2001 and Iraq in 2003. The UK fleet has slowly been reduced from 7 since 2011. In 2009, the UK effectively limited the service life of the E 3D fleet by de funding the Project Eagle upgrade which would have seen it upgraded in line with the USAF Block 40/45 standard. AirForces Monthly reported that by December 2020, just 2 aircraft were available for operations at any one time. The £1.51 billion contract was awarded to Boeing without a competitive procurement process, a decision criticised by both competitors of Boeing and the UK's Defence Select Committee. The 2021 Integrated Defence Review confirmed a reduced order of three aircraft. On 27 January 2015, the RAF deployed an E 3D Sentry to Cyprus in support of U. S. led coalition airstrikes against Islamic State militants in Iraq and Syria. The last intended operational flight by an RAF E3 Sentry was supposed to be in July 2021 with the Sentry retired from service, however RAF ZH101 and ZH106 have both flown patrols over Poland / Eastern Europe during Russia's incursions into Ukraine during late February / March 2022.

In February 1987 the UK and France ordered E 3 aircraft in a joint project which saw deliveries start in 1991.

3 Boeing E 3D Sentry (Sentry AEW.1) aircraft, acquired second hand from the United Kingdom in September 2021, arrived in Chile in July 2022; units ZH103 and ZH106 will join the "Grupo de Aviación N.º 10" of the II Air Brigade.

NATO acquired 18 E 3As and support equipment, with the first aircraft delivered in January 1982. The aircraft are registered in Luxembourg. The eighteen E 3s were operated by Number 1, 2 and 3 Squadrons of NATO's E 3 Component, based at NATO Air Base Geilenkirchen. NATO and RAF E 3s participated in the military intervention in Libya. From January 2011 to September 2014, NATO E 3s were deployed to Mazar i Sharif International Airport, Afghanistan, as part of NATO's International Security Assistance Force (ISAF) mission. The aircraft were used for air traffic control of military aircraft over the country, as well as surveillance, and tactical management of friendly aircraft. During the mission to Afghanistan, NATO E 3s flew 1,240 missions and accumulated 12,240 flying hours. Presently, 14 NATO E 3As are in the inventory, since one E 3 was lost in a crash and three were retired from service in 2015, 2017, and 2018. The first was due for its six year cycle Depot Level Maintenance (DLM) inspection which would have been very costly. The "449 Retirement Project" resulted in reclamation of critical parts with a value of upwards of $40 million which will be used to support the remaining active aircraft. Some of the parts to be removed are no longer on the market or have become very expensive.

[[File:Boeing E 3 Sentry LX N 90454 3. JPG|thumb|NATO E 3s possess LX tail registration, One additional aircraft retained by Boeing for testing, E 3G(II) Block 40/45 modification that included a glass cockpit modification that reduced the crew size by one, and added a new avionics suite.