Sentry AEW Mk1

Airframe

The Sentry AEW Mk1 is built on the Boeing 707-300 series airframe.  The four CFM 56 engines have reverse thrust, and are efficient and quiet.  Given sufficient runway length, the aircraft can stay airborne for over 10 hours.  This time can be extended by air-air refuelling: the E-3D has both “drogue and probe” and “boom receptacle” AAR systems, and can accept fuel from most US and UK/NATO tankers.  The main limitation to airborne time is crew fatigue.

Mission Equipment

Surveillance Radar

The main sensor of the E-3D Sentry is the AN/APY-2 surveillance radar, built by Northrop-Grumman.  The multimode radar has both pulse doppler (PD) and basic pulse modes, which allow it to detect targets out to 300 nautical miles.  The PD radar allows look-down capability, over all terrains, out to the radar horizon (which is 210 miles at the normal cruising altitude of 29,000 ft).  One aircraft flying at 30,000 feet has a radar coverage of 312,000 square kilometers.  Three aircraft in overlapping orbits can provide complete radar coverage of all of Central Europe.  The pulse radar is used in the “Beyond the Horizon (BTH)” mode and therefore avoids ground clutter.  It is also used to detect shipping out to the radar horizon when used.  The radar system was upgraded in 1999 to “Radar System Improved Package” (RSIP) standard, which gives detection of smaller stealthy targets.

IFF Interrogator

The surveillance radar is supplemented by an IFF interrogator, which allows the identification of friendly targets.  Modes 1, 2, 3A, 3C and 4 are available together with operator alerts for certain “emergency squawks” such as mode 3A 7700.  The IFF antenna is mounted back to back with the main radar antenna in the large mushroom shaped radome on top of the aircraft fuselage.

Electronic Support Measures (ESM)

All transmissions from a radar set are unique to that type of radar, and can be identified by anyone with a suitable radar frequency receiver and a decent database of radar parameters.  The E-3D Sentry is fitted with the Loral 1017 “Yellowgate” ESM system, unique to the E-3D within the AEW world, located in the aircraft's distinctive wing pods.  This system gives automatic identification of radar transmissions together with a bearing of that radar’s source.  This allows the ESM operator some degree of identification of radar contacts in a tactical situation.

Mission Computer

Sensor data are processed by the on-board computer and presented to the E-3D mission crew via ten “Situation Display Consoles.”  The operators track these contacts – information such as position, heading, speed, height and identification is also stored in the computer.  This track information can be passed to other computer systems, either on the ground or in ships and other aircraft, via data links.

Communications

The E-3D can pass information by a variety of data links, and radios.  Voice communication is achieved via satellite communications, UHF, VHF and HF voice radios.  Data can be passed by data link.  The main links include:

Joint Tactical Information Distribution System (JTIDS)  JTIDS uses both Interim JTIDS Message Standard (IJMS) and Link 16 message standards.  Link 16 is used to pass tactical information between the E-3D and the Tornado F3's and Typhoon's.  IJMS is the main NATO air-picture data link.

Link 11  Link 11 is used to pass data to Naval Forces, UK air-defence sites and to some air platforms such as maritime patrol and Elint aircraft.

Link 4 and Link 14  Both where originally installed but are no longer used.

Seven different internal communication nets allow the crew to co-ordinate internally, either discretely or crew-wide.  Three of these nets are capable of carrying classified information without risk of interception.