E-3 SENTRY gallery

(USAF’s E-3 image). E-3 Sentry arose from the need to replace the Lockheed EC-121 Warning Star, which had been the main AEW&C aircraft in the USAF and the US Navy for a decade. This time, two prototypes were built to adapt and test two pulse-Doppler radars presented by Hughes and Westinghouse companies. This last would be the winner of the contest.
(USAF’s E-3 image). The prototypes were designated as EC-137D, and they were Boeing 707 airliners with a rotating radome with radar inside installed. These prototypes kept the B-707’s engines, which granted sufficient range for tests, although they would be replaced by others in the production aircraft. Radar tests were conducted between March and July 1972.
(USAF’s E-3 image). Finally the Westinghouse radar was the winner. The radar was designated as AN/APY-1 ODR (Overland Downlook Radar) and used an 18-bit AYK-8-EP1 computer. This element could be programmed before each mission and had a beyond-the-horizon (BTH) pulse mode. This mode was especially effective detecting ships when the radar pulse was directed beyond the horizon, below the aircraft line of flight.
(USAF’s E-3 image). The E-3A Sentry entered service in 1977 and carried Pratt and Whitney TF33-PW-100A engines, an IBM 4PiCC-1 mission computer and a Semi-Automatic Ground Environment (SAGE) system. SAGE allowed the automatic sending of radar traces to different control centers of the North American Aerospace Defense Command (NORAD) to improve decision making in real time.
(USAF’s E-3 image). The soul of the E-3A Sentry system was the AN/APY-1 passive electronically scanned array radar system. It was installed inside a huge rotating radome, (or rotodome), of 9.14 meters in diameter and 1.8 m thick at the center. The rotodome weighed 1,540 kg and was tilted 2.5º down to reduce aerodynamic drag, is attached to the fuselage of the aircraft by two struts and when it is operating rotated six times per minute. This radar is capable of monitoring an area of 312,000 km2 and is so effective that it can detect and track cars traveling on highways.
(USAF’s E-3 image). The radar antenna measured 7.32 x 1.52 meters and was a high recurrence PRF (Pulse Repetition Frequency) system. This system permited downwards exploration, which used the Doppler effect to distinguish the moving targets from the so-called “fixed echoes”. The radar performed a 360º sweep and could detect mid-high altitude flying aircraft from 650 km away and low-flying altitude aircraft from 400 km away. The Sentry have an operational flight altitude of 9,000 meters and the radar covered from the Earth’s surface to the stratosphere over land and sea.
(USAF’s E-3 image). This radar had 5 modes of operation: -two for tracking flying aircraft at any level, known as PDES and PDNES modes; -one for tracking mid-high altitude flying aircraft called BTH (Beyond The Horizon) mode, and which did not use Doppler pulses; -one for maritime surveillance, which eliminated the disturbances caused by the waves; and a passive listening mode to locate the enemy ECM transmitters. The scanning of the antenna can be divided into 12 sectors, and in each of them it is possible to use different modes or combinations thereof.
(USAF’s E-3 image). An E-3 Sentry‘s typical mission lasts about 11 hours, although it is usual that after refueling in flight, this mission reaches 18 hours. The crew consists of about 20 people, 16 of whom are weapons controllers, radar operators and communications specialists. They usually work in shifts, being able to rest in an area fitted for it located in the rear part of the fuselage. The radar can follow the flight of about 600 aircraft in low altitude flight. The data obtained allow the High Command to plan the different missions of ground support, interception, reconnaissance or any mission that may be needed at any given moment.
(USAF’s E-3 image). USAF’s E-3A Sentry began its mission of US continental air defense in January 1979 and have subsequently been receiving improvements that have led to new variants. In July 1984, the 552nd AW & CW received the first E-3B Sentry from the 24 that were converted to this variant. The first example was modified by Boeing, and the following ones were modified by the USAF in the Tinker AFB, Oklahoma, with equipment supplied by Boeing.
(USAF’s E-3 image). The E-3B received modifications designated as Block 20. They consisting of an IBM CC-2 mission computer, more resistant communications to the ECMs, additional radios, five more electronic control consoles and a “Have Quick” secure communications system. In 1991 through the “Project Snappy”, 15 E-3B were equipped with an additional sensor, (unknown to date), to participate in Operation Desert Storm, where they were essential in the successful Allied air campaign.
(USAF’s E-3 image). In 1984, the remaining 10 E-3A were modified to the E-3C variant. They received new Westinghouse AN/APY-2 radar, 5 additional electronic control consoles, new radios, “Have Quick” secure communications system and a slight increase in the number of crew members.
(USAF’s E-3 image). In 1987, a new improvement program, designated as Block 30/35, began to be implemented on the USAF’s E-3 Sentry fleet. Among these improvements are the Joint Tactical Information Distribution System (JTIDS) that transmits information quickly and safely to other friendly platforms, including data on enemy targets. In addition, a GPS system, active and passive electronic detection and surveillance systems, new computers and the new Link-16 military tactical data link network were added. This program culminated in October 2001.
(USAF’s E-3 image). The radar was also improved under the so-called Radar System Improvement Program (RSIP). This update was focused to the replacement of analog electronic components by other digital and computerized ones that greatly improve the reliability and maintenance of the equipment. In practice, the new radar has much greater capacity to detect targets with low radar signature and more effective electronic countermeasures.
(NATO’s NE-3A image). In December 1978, NATO decided to buy 18 E-3A Sentry to be operated jointly by the member countries. It was decided to register all the aircrafts in Luxembourg, which did not have Air Force. In February 1982, they began the aerial operations of these aircrafts, which were based on the Geilenkirchen NATO Air Base, Germany. These aircrafts are officially designed as NE-3A.
(NATO’s NE-3A image). NATO’s NE-3A is part of the NAEW & CF (“NATO Airborne Early Warning and Control Force”) and they are framed in 3 Squadrons plus another training and transport that has 3 B-707-329C (CT-49A) aircraft. Currently there are 16 active aircraft, since one was lost in an accident and another was retired in 2015.
(NATO’s NE-3A image). Sixteen countries are involved in the NAEW & CF program, of which 15 send personnel to operate the NE-3As in joint crews and Luxembourg collaborates financially to maintain the unit. The “E-3A Component”, as this unit is called, is the only military air unit in the World that is composed by personnel from different countries that act together under a single command.
(NATO’s NE-3A image). The E-3A Component is composed of five main operational areas, designated as: “Operations”, “Logistics”, “Ground Support”, “Training” and “Technology”. There are other support detachments and services too. All these areas depend on the SACEUR (“Supreme Allied Commander Europe”), which is the organism in charge of selecting and directing the missions of these aircrafts. Missions range goes from aerial surveillance in conflict areas to the surveillance of sporting events, international political summits and events of high significance and importance.
(NATO’s NE-3A image). Several NE-3A are permanently deployed in three “Forward Operating Bases” (FOB) located in Aktion, (Greece), Trapani, (Italy), and Konya, (Turkey). There is a fourth location known as “Forward Operating Location” which is located in Orland, Norway. This way, all NATO’s borders are kept under surveillance, especially those of the southern zone, near to the Mediterranean.
(NATO’s NE-3A image). The crew is currently composed by 17 people, although it can be raised to a maximum of 35 depending on the type of mission. Four make up the “flight crew”, who drive the aircraft. Five more make up the “surveillance team” they manage and offer all information captured by the radar. Three more are the “armament team”, which is responsible for guiding the Allied aircraft under control of the NE-3A and the rest of the crew consists of “tactical director”, the “communications operator” and three “maintenance technicians” “, one of communications, one of data presentation and one of radar.
(NATO’s NE-3A image). The NE-3A have also received several modernizations, the first in 1987 with the improvement of the ESM (“Electronic Support Measures”) capabilities. From 1993 to 1997 new screens and consoles were added, UHF Have Quick radios, protection against external interference and the ESM Quick Look system (AN / AYR-1). This device is capable of detecting radar emissions more than 500 km away. Between 1996 and 2000, the RSIP (“Radar System Improvement Program”) was carried out along with the updating of electronic counter-countermeasures, new control consoles, new software and improvements to the on-board computer. One of the latest additions has been the LAIRCM system (“Large Aircraft Infra-Red Countermeasures”), based on the AN / AAQ-24 (V) Nemesis system. This equipment operates automatically (without the crew doing anything), detecting the launch of a missile and determining if it is a threat or not. If the system thinks it is an attack, it directs a high intensity laser beam to the IR sensor of the missile, which is disabled.
(RAF’s E-3D image). In 1987, after cancellation of Nimrod AEW Mk.3 program, the RAF requested seven E-3D Sentry. D variant is similar to E-3C variant but with CFM56-2A-3 engines and various indigenous modifications. These 7 aircraft were framed in the RAF’s 8th Squadron, based in Waddington, England, and are part of the NAEW & CF (“NATO Airborne Early Warning and Control Force”), although they are operated by entirely British crews. These crews consist of 17 members, four from the flight crew, one communications officer, three maintenance technicians, three surveillance operators, one data transmission operator, one ESM system operator three mission specialists and one tactical director.
(RAF’s E-3D image). RAF’s E-3D have significant differences with the other E-3 aircrafts. The engines, an external flight refueling probe and containers at the tip of the wings where ESM Loral 1017 “Yellow Gate” equipment is housed for detection of passive radars. This equipment was tested by the Americans E-3 in some fairings installed on the sides of the front fuselage. Thanks to the CMF56 engines, the range without refueling exceeds 10 hours.
(RAF’s E-3D image). Currently, RAF operates four E-3Ds plus one for training, having recently retired two aircraft. In addition to the United Kingdom and the USA, only France and Saudi Arabia operates E-3 Sentry. France has four E-3Fs, similar to the E-3C variant but with CFM56 engines and various specific  modifications. On the other hand, Saudi Arabia operates five E-3As with CFM56 engines and five KE-3A in-flight refueling aircraft.


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