The E-3 Sentry was first deployed in 1977, replacing the older EC-121 Warning Star which served in Vietnam. Basically a 707 airliner with a nine-meter diameter APY- 2 radar rotating on top, the E-3's 13 to 19 crew members can track aircraft and ships from as far as 250 miles away.The Sentry is particularly useful for detecting aircraft flying below the effective altitude of surface-based radars. The E-3's 20 high- and ultra-high frequency radios allow the crew to communicate with and direct friendly forces.Today the US Air Force operates a fleet of 32 E-3s across the world, while European NATO countries share a fleet of 16 Sentries based in Geilenkirchen, Germany. Smaller numbers also serve in the air forces of France, the United Kingdom, and Saudi Arabia.The E-3G Block 40/45 upgrade replaces the Sentry's antiquated computers with a Red Hat Linux-based system for the main flight computer, and Windows-based operator workstations, which are connected to each other via a local area network. These will provide a new user interface and application for 15 crewmembers.Read more: The US Air Force's Biggest Spy Planes Are Hunting ISIS Fighters
The first upgraded E-3G at Tinkers Air Force Base in Oklahoma in 2010. Photo: USAF
E-3 of 552nd Air Control Wing takes off from Nellis Air Force Base during Red Flag 16-2 exercise in March 2016. Photo: USAF
"The primary cause of errors is traceable to legacy analog sensors, which were not upgraded as part of the Block 40/45 modification. Block 40/45 integrates data inputs from multi-sensor on-board and off-board systems, which provides the operator with a "single target-single track" capability. The current version of AWACS, Block 30/35, does not integrate its information to provide a single track, so the mission crew must take the information provided and manually create tracks from different sensor and communications datalinks."