Continuing Support and Modification
Modification work and post-production support for the E-6 fleet continues at Boeing facilities in Seattle, Wash.; Wichita, Kan.; Huntsville, Ala.; and Jacksonville, Fla.; and at E-6 operational sites at Tinker Air Force Base, Okla., Travis Air Force Base, Calif., Offutt Air Force Base, Neb.and Patuxent River Naval Air Station, Md. Modification and training programs carried out by Boeing ensure that the airplane and flight crews have the information, equipment and tools needed to adapt to changing requirements. Among the improvements:
- A series of post-production reliability and maintainability upgrades, including tail-section modifications, were completed in Wichita in late 1993. (The first three aircraft were modified in Seattle.)
- A new digital auto-pilot system to replace the airplane's original analog system was designed and flight tests completed in May 1994. The upgrade improved reliability and maintainability, while facilitating future modifications to the airplane to improve its orbit capabilities. Production installations were accomplished by Boeing field teams at Tinker in 1995.
- Orbit Improvement System (OIS) enhancements were designed and tested under a $22 million development contract. The new system improves communication effectiveness by suppressing vertical oscillation ("yo-yo") of the long trailing wire caused by wind shear. The OIS modification includes installation of an auto-throttle system adapted from the two-engine 737 for the four-engine systems and unique orbit flight profiles of the E-6, as well as modification of the flight management computer. Both the auto-throttle and the flight-management computer (FMC) were developed and procured under a subcontract to Smiths Industries in Cheltenham, England.
The OIS design also integrates the auto-throttle built-in test equipment (BITE) capabilities of modern 737 designs. The BITE will provide for flight-line maintenance testing, fault detection and continuous in-flight monitoring of the auto-throttle system. Benefits to the Navy will include minimization of on-aircraft maintenance time, reduction of unconfirmed failures, and improved identification of failed components and associated interfaces.
Installation and test of the initial OIS started in early 1995 and was completed in September 1995. Flight testing during that period proved that the upgrade does, in fact, significantly improve the airplane's ability to perform orbit maneuvers at high bank angles. A $16 million follow-on contract for retrofit of the remaining E-6 aircraft was awarded in late 1995. Aircraft modification was performed by Boeing field teams at Tinker from September 1996 through August 1997. A follow-on upgrade of additional OIS software features will be fielded in 1998-99.
- Electronic horizontal situation indicator (EHSI) and attitude direction indicator (EADI). Together with the OIS program, Boeing integrated, installed and demonstrated an EHSI and EADI flight instrument system. Replacement of the existing analog horizontal situation indicator (HSI) was necessary to facilitate integration of global-positioning system (GPS) requirements in the E-6. Simultaneous replacement of the analog attitude direction indicator (ADI) will provide flight deck commonality and improved maintainability.
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Modification of trainers. In March 1994, Boeing was awarded a $10.8 million contract to upgrade 10 E-6 maintenance trainers. The trainers are assigned to the Naval Air Maintenance Training Detachment at Tinker. The trainer modification contract incorporated various aircraft production revisions and engineering changes, as well as Navy instructor-initiated design enhancements. A total of 168 modifications were designed and installed into the various trainers as part of the contract. The modified trainers were redelivered to the Navy between November 1994 and July 1995.
Boeing initially delivered the trainers to the Navy in 1989 and 1990 under the original aircraft production contract. They provide a training platform for hands-on maintenance testing, troubleshooting, and removal and replacement of aircraft systems components for E-6 maintenance technicians.
The trainers cover a range of specialized areas including integrated avionics, landing gear, power plant, flight control aft lower lobe, electrical systems, environmental control systems, auxiliary power unit, hydraulic system and fuel systems.
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Frequency Reference Auto-Paralleling Unit (FRAPU). In the spring 1996, Boeing integrated and installed the first E-6 FRAPU. The FRAPU itself is a "black box" manufactured by Sundstrand. When installed in the aircraft's electrical power generation and distribution system, the FRAPU precludes any momentary loss of electrical power when shifting the source of aircraft electrical power from ground power carts or the onboard auxiliary power unit (APU) to the normal source of inflight power, the eight generators driven by the aircraft's CFM-56 engines.
This modification enhances mission capability by eliminating operational delays to re-initialize mission systems and computers that would otherwise have been disrupted by power losses. It also is expected to improve system reliability and reduce maintenance by eliminating power surges and transients that can damage equipment.
Installation of FRAPU in the remaining 15 aircraft was accomplished by Boeing field teams at Tinker in fall 1996 and early 1997.