NATO Airborne Early Warning and Control Aircraft: Hawkeye and Sentry – The Workhorses of Radar Surveillance
Boeing E-3 Sentry
Continuation, part one: NATO Airborne Early Warning and Control Aircraft: How the Class Was Born
E-2 Hawkeye: The First Carrier-Based AWACS Built from Scratch
In 1956, the US Navy formulated requirements for an airborne early warning and control (AEW&C) aircraft whose data could be integrated into a ship's tactical data processing system. In March 1957, the Grumman design was selected. Its design, initially designated the W2F-1 and later renamed the E-2A Hawkeye, became the first carrier-based aircraft designed from the ground up specifically as an AEW&C aircraft. Unlike previous aircraft in this class, which were converted from existing aircraft, the Hawkeye was created specifically for this mission.
The designers faced serious challenges. Chief among them was the requirement to base the aircraft on modified Essex-class carriers, built during World War II and smaller than modern ships. This resulted in strict restrictions on height, weight, and length, and with them, reduced handling. Ironically, the aircraft never flew from the Essex: the restrictions were based on a scenario that never materialized. A second challenge was cooling the tightly packed avionics bay, discussed below.
The first prototype—essentially an aerodynamic testbed—took to the air on October 21, 1960. The first fully equipped aircraft flew on April 19, 1961, and the aircraft entered service with the U.S. Navy under the designation E-2A in January 1964. Due to a series of problems, production was limited—only 59 aircraft were built. The main issue was cooling: in the tightly packed avionics bay, the early computers generated a lot of heat and failed without proper ventilation. Problems persisted even after the aircraft entered service—at one point, reliability deteriorated so much that the entire fleet was temporarily grounded.
Navy representatives had to explain to Congress why four production contracts were awarded before avionics testing was complete. After that, they began refining the aircraft in earnest. The unreliable rotary drum computer was replaced with a digital Litton L-304, and other systems were also updated; the upgraded aircraft were designated E-2B. A total of 49 of the 59 E-2As were upgraded to E-2B standard (with a central flight computer). The Hawkeye was replaced in US Navy AWACS squadrons by the E-1B Tracer. The entire E-2A/B series, with its powerful APS-96 radar (capable of tracking over 100 targets simultaneously), was retired by the mid-1980s.
Standard deck-based AWACS and U for aviation The E-2C variant (first flight on January 20, 1971) with the APS-125 radar and improved avionics became the US and NATO choice. The series was continually improved, with the addition of the APS-138, APS-139 (since 1989), and APS-145 radars. The latter, with a new antenna system and signal processing unit, provided better protection against jamming and expanded aerial reconnaissance capabilities. The onboard computer was also updated: the Raytheon Model 940 was superior to the previous L-304—it was half the weight, three times more compact, and 15 times more energy efficient in terms of average power consumption. The open architecture of the avionics allowed for the expansion of the equipment set, including reconnaissance; new communication and identification friend or foe systems were also added. In total, more than 200 E-2s of all modifications were produced (production is still ongoing, now in the E-2D version), and the exact number of E-2Cs differs in sources.
In early 2007, Northrop Grumman unveiled the first of its next-generation aircraft, the E-2D Advanced Hawkeye, at its facility in St. Augustine, Florida. Its maiden flight took place on August 3 of that year. The E-2D is equipped with a Lockheed Martin AN/APY-9 electronically scanned array radar, which significantly expands search capabilities and functions as an airborne combat management system. A new radio, a new onboard computer, and an in-flight refueling system were also added. The prototype on display was the first of two prototypes built during the $2 billion System Development and Demonstration (SDD) phase of the system; the U.S. Navy contract for this phase had been awarded back in 2001. The Navy subsequently ordered 75 of these aircraft, with plans to supply them for the next two decades.
The program was surprisingly long: the E-2A airframe survived until the E-2D almost unchanged—only the avionics changed. The E-2's mission is different from the E-3, which is discussed below. The E-2 operates from the deck, serving its air group. The E-3 is a ground-based aircraft, operating at the operational-strategic level, not for a single air group.
E-2C Hawkeye aircraft
The E-2 Hawkeye is in service with the US Navy, as well as the naval and air forces of Egypt, Israel, France, and Japan. Since 1997, the US Navy's E-2C avionics have been upgraded under the Hawkeye 2000 program.
Hawkeye 2000
E-3 Sentry: The most widely deployed AWACS in the world
On January 26, 1973, full-scale development of the AWACS program—both the system and the carrier aircraft—was approved, and three pre-production aircraft were ordered. The first of these took to the air in February 1975.
The civilian Boeing 707-320B was used as the base—a wide airframe with ample headroom, energy efficiency, and range. This headroom later proved useful: it was able to accommodate increasingly powerful equipment, and after structural fatigue repairs, the airframe itself is expected to remain in service until 2035.
The onboard computer and display system were developed by IBM and Hazeltine: the IBM computer was designated 4PI, and the software was written in the JOVIAL language. The concept was to provide the operator of the ground-based SAGE air defense system or the backup interceptor control system (BUIC) with real-time trajectory and tabular data. A separate complication arose: discrepancies in data encoding formats adopted by the US Air Force and allied forces hindered interoperability with tactical ground-based radars in Iceland, continental Europe, and South Korea when operating via the Link-11 (TADIL-A) data link.
Engineering testing and flight testing of the first production E-3 Sentry began in October 1975; it first flew on May 25, 1976. Between 1977 and 1992, 68 production E-3 Sentries were built. (There was also a failed deal: in 1977, Iran ordered ten E-3s, but the order was canceled after the Iranian Revolution.)
The E-3 Sentry, which entered service with the U.S. Air Force in 1977, remains the most widely used AWACS aircraft in the world. The first aircraft was delivered to the 552nd Airborne Warning and Control Wing, arriving at Tinker Air Force Base, Oklahoma, on March 23, 1977. The Air Force received the last of its Sentries in June 1984.
Of the 68 E-3s built, approximately 42 went to the USAF, 17 to NATO (E-3A), 5 to Saudi Arabia, and 4 (E-3F) to France. The number of American aircraft in service fluctuated over time—decommissionings, losses, and conversions—so sources specific to a specific year often provide lower figures. The majority of American aircraft were based at Tinker Air Force Base and assigned to the Air Combat Command (ACC); some were assigned to Pacific Air Forces (PACAF) at Kadena Air Force Base, Okinawa, and Elmendorf Air Force Base, Alaska. One trainer (TS-3) was transferred to Boeing for testing and development and was retired in June 2012.
Several modifications were created, including:
E-3A — the first aircraft for NATO, the US Air Force, and the Saudi Arabian Air Force (the latter with CFM56-2A-2 turbofan engines). The basic powerplant is four TF33-PW-100A turbofan engines with a thrust of approximately 95–96 kN (9700–9800 kgf). Some sources cite a lower value of 93,4 kN. Between 1977 and 1979, 25 US Air Force aircraft were converted to the E-3B variant. It had an improved airframe resistance to the damaging effects of a nuclear explosion—EMP, gamma, and neutron radiation. A faster CC-2 processor, jam-resistant communications, and an improved radar were also installed.
The antenna array is housed under a rotating dome—30 feet (9,1 m) in diameter and 6 feet (1,8 m) thick at the center. The dome is supported 11 feet (3,4 m) above the fuselage by two pylons. It is unpressurized and cooled using its own cooling system: bleed air, external cooling doors, and a fluorocarbon system. The forward part of the dome is slightly inclined downward to reduce drag; the resulting beam distortion is compensated for by electronic phase shifters for the radar and secondary radar antennas. The rotodome is served by an AN/APY-1 or AN/APY-2 passive phased array radar: electronic scanning for altitude and mechanical scanning for azimuth, thanks to the rotating dome. The radar detects airborne targets from the surface to the stratosphere, over land and over water, with rejection of ground and water clutter. According to the developer, in pulse-Doppler mode the range exceeds 250 miles (400 km) for low-flying targets at operating altitude, and in pulse mode – about 400 miles (650 km) for aircraft at medium and high altitudes.
E-3c — nine US Air Force aircraft built between 1981 and 1983 with additional equipment.
E-3D — six aircraft of the Royal Air Force (designation AEW/Mk1), in service since 1990. The power plant is four CFM56-2A-3 turbofan engines with a thrust of approximately 106–110 kN (10,800–11,200 kgf).
The US and NATO E-3As fly over 5000 nautical miles (9300 km) without refueling and remain airborne for eight hours. French, Saudi Arabian, and British aircraft, equipped with more advanced CFM56-2 engines, remain airborne for approximately 11 hours and have a range of over 9250 km (5750 mi). Their range and patrol time are extended by in-flight refueling, and the crew works in shifts—there is a rest area on board. Their special equipment includes a number of British systems, including the LORAL 1070 "Yellow Gate" in wingtip pods. A probe for an in-flight refueling system is also installed.
E-3F — four aircraft of the French Air Force, the first accepted in 1990. They feature some French-made equipment, such as the Adele radar warning system.
Since 1995, the Block 30/35 Radar System Improvement Program (RSIP) has upgraded the U.S. Air Force E-3B, NATO E-3A, and aircraft from the United Kingdom, France, and Saudi Arabia. The goal was to improve the onboard radar, increase its jamming immunity, and double the detection range of small targets. At the same time, the AN/AYR-1 electronic intelligence station, NAVSTAR satellite navigation receiver, and new communications equipment were introduced. According to the developer, the AN/AYR-1, with a range of up to 600 km, detects and identifies types of electronic equipment and their carriers with an accuracy of 50-100 meters.
Under the EAGLE (Extended Airborne Global Launch Evaluator) program, Boeing retrofitted the E-3 with a passive optical-electronic system for detecting operational-tactical and ballistic missiles. missiles Medium- and intercontinental-range missiles—this allowed the E-3 aircraft themselves to be integrated into theater missile defense systems. For this purpose, an infrared detection and precision tracking station, a laser rangefinder, high-performance processors, and communications equipment were installed onboard.
Re-engining was discussed separately to reduce operating costs, improve performance, and preserve the fleet until 2035. The E-3's standard engine is the TF33 (the civilian JT3D), and the CFM56 was considered as the primary replacement, but this never materialized for the US Air Force fleet. Airframe and control surface fatigue, however, were addressed separately, adding 18,000 hours to the service life. Modern systems consume more energy, so the aircraft are receiving new generators and batteries.
Since the early 2000s, the US and NATO countries have been upgrading their onboard computer systems and display systems. They have successfully transitioned entirely to open-architecture systems, which are easier to scale and update. Operator workstations operate in a Windows-like environment, offering a more user-friendly interface and reducing crew workload. After software upgrades, the Multi-Sensor Integration (MSI) system, which integrates data from multiple sensors, gathers everything into a single network and facilitates interactive exchange between the crew and the avionics. An improved signal processing unit has enabled more accurate target tracking and allows for detailed maps. Five operator workstations have been added to the E-3, providing access to external network sources (maps, weather data) and real-time database updates. The cockpit has also been redesigned to reduce the information load. According to US specialists, this has significantly reduced crew training time and the need for training aircraft.
The main focus of work on advanced AWACS and CAS was the transfer of control and guidance functions to ground-based command posts and, eventually, to spacecraft. This was the focus of the Mission Crew to Ground (MCG) program: only the flight crew, communications operators, radar technicians, and technicians were expected to remain onboard. The entire AWACS dataset would be transmitted to the ground, where it would be processed along with data from reconnaissance UAVs. This was expected to improve the operational efficiency of AWACS and CAS and reduce the number of crews. In parallel, work was underway on the combined use of AWACS and CAS with reconnaissance UAVs for over-the-horizon detection of low-altitude targets. It is difficult to judge from the available data whether the MCG has reached actual implementation and has not remained a research program.
In any case, the E-3 has remained the backbone of US and NATO long-range radar surveillance for nearly half a century—and, judging by service extension programs, will remain in service for a long time to come. What they plan to replace it with will be discussed in the next section.
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