Boeing 717 Overview

The 717 (formerly the MD-95) is the newest twin-jet model in the Boeing product line. It resembles the DC-9 in size, range, and performance, and retains many of the structural design characteristics that earned the DC-9 a reputation for superior reliability. Incorporated in the 717 are several advanced systems that enhance flight operations and improve maintainability. Flight test is scheduled to begin in mid-1998, with type certification and first delivery planned for June 1999.

The latest twin-jet offering from Boeing is the 717, an airplane that began with the best attributes of the DC-9 and improved on them for increased operator benefit.Though the 717 shares its wing size with the DC-9, the new airplane offers 57 more inches of fuselage forward of the wing than the DC-9 Series 30. The 717 seats 106 passengers in a two-class configuration, and 117 in a single-class configuration.The 717 will operate up to the same maximum weights as the DC-9 Series 50 with a range of 1,570 nautical miles (nmi).

The 717 incorporates a "three-wheel" air-conditioning pack. This eliminates the need for electric air-conditioning ground cooling fans by providing air flow from the third wheel across the heat exchanger. The third wheel functions any time the air-conditioning pack is operating. A dedicated fan has been added to the tail compartment to provide cooling and ventilation in the aft compartment during ground operations.

The cabin pressurization control system incorporates a single, electrically controlled outflow valve. This reliable single-valve design eliminates the manual pressurization wheel from the flight deck pedestal and all associated cable runs throughout the airplane. The flight crew can press a button on the overhead panel to put the system in manual mode. Cabin pressure can then be controlled using a momentary three-position toggle switch on the same panel.

The 717 air-conditioning pack offers a high-flow operating mode that provides superior cabin cooling capabilities at high ambient temperatures. The high-flow mode also improves the clearing of cigarette smoke from the cabin. The normal and high-flow modes are manually selectable. Like the DC-9, the 717 does not recirculate cabin air, but instead provides 100-percent fresh air for cabin ventilation and pressurization.

The 717 passenger cabin offers spacious styling and the popular five-abreast seating arrangement. It also incorporates several new features that enhance maintainability and passenger comfort:

Three-bay sidewall panels. These new panels enable maintenance personnel to access the inner and outer window panes and window-shade assembly without removing sidewalls or seats. A new, solid window shade is more durable than previous styles and blocks more light. Only a Phillips-head screwdriver is required to remove sidewall panels, and no tools are required to remove the ceiling panels.

Larger overhead stowage compartments. The overhead stowage compartments standard in the 717 offer more volume capacity than those in the DC-9. An optional, asymmetric compartment provides even more stowage space per passenger. The compartments are modular for easy replacement, and installation procedures are standardized for all units. The compartments are equipped with a full-grip, lighted handrail that extends the length of the passenger cabin.

Improved lighting system. The 717 cabin lighting system incorporates solid-state, flicker-free ballasts with selectable, preset cabin-illumination levels. All attendant call and passenger reading lights can be turned on or off from a single switch, a feature that helps maintenance and cabin crews during lighting checks and aircraft preparation. A new, seat-mounted emergency escape path lighting system has a longer service life and lower associated maintenance costs compared to traditional, floor-mounted systems.

Modular lavatories. The modular design of these lavatories permits easy removal and installation. Vacuum waste toilets reduce cabin odors and require less time for servicing. The lavatories are also equipped with smoke detectors and trash-receptacle fire extinguishers.

The 717 flight deck incorporates six 8-by-8-in, liquid crystal displays (LCD) that present all essential information related to flight, navigation, engines, and systems. The LCDs replace several individual instruments used on DC-9 and MD-80 flight decks to reduce dramatically the number of instruments and line-replaceable units (LRU). The LCDs also provide a cleaner, uncluttered appearance, and improve the presentation of information.

Flight deck improvements include:

Synoptic displays.The system display includes 10 selectable displays, including synoptic displays for the hydraulic, environmental, electrical, fuel, airplane configuration, and engine systems. The system displays provide data on system status, failures, system configuration, and operating modes.

Integrated flight crew warning & alerting system. The LCDs present data from the integrated flight crew warning and alerting system. This integrated function replaces the electronic overhead annunciator panel, dedicated annunciator lights, analog gauges, and other dedicated system status lights on the overhead panel. The remaining overhead panel switches are logically grouped by airplane system, and are divided according to left, right, and auxiliary systems for easy selection.

Flight control computers (FCC). FCCs provide the 717 with full Category IIIa autoland capability. Full Category IIIb operation is available with the addition of an optional radio altimeter, instrument landing system receiver, and an inertial reference unit. The FCCs replace a number of avionic LRUs in previous twin-jets by performing the functions of the flight guidance computer, stall warning computers, windshear computers, and auxiliary control unit.

Versatile integrated avionic computers.Two versatile integrated avionic (VIA) computers process data for display on the LCDs. The VIAs also perform the function of the flight management system (FMS), central aural warning system, and flight data acquisition system. The dual FMS is capable of supporting advanced navigation functions such as the Global Positioning System, Future Air Navigation System, and pilot/controller datalink. All communication, navigation, and surveillance radios conform to current ARINC 700 standards, and a digitally controlled audio system is standard equipment.

Centralized fault display system (CFDS).The CFDS allows maintenance personnel to interrogate most system LRUs from a single location in the flight deck. The CFDS displays system faults, fault history, and sensor readouts. It is also used to perform return-to-service and trouble-shooting tests.

Air data inertialreference unit (ADIRU).The ADIRU combines the functions of the air data system and inertial reference unit. The ADIRUs receive digital pitot and static pressure data from air data modules located adjacent to the pitot tubes and static ports. The new design reduces the amount of pitot/static tubing and eliminates requirements for leak checks following component replacement. The standby instruments used on the DC-9 have been replaced with a single integrated unit with its own air data modules.

Primary electrical power for the 717 is provided by two engine-mounted, 35/40 kilovoltampere (kVA) integrated drive generators and a 60 kVA APU generator. Each generator is controlled by a power conversion and distribution unit (PCDU), which performs the functions formerly provided by a generator control unit in conjunction with the transformer rectifier, bus tie relays. The three PCDUs are identical to reduce spares requirements and maintenance costs.The primary electrical power relays are modular and mounted to the front of the PCDU for easy replacement. An electrical power control unit controls the overall electrical system, including the no-break power transfers, external power, and system protection.The following installation features simplify the repair and troubleshooting of many systems:

An improved ground service power function allows single-switch operation of the ground service bus, while minimizing the power cycles to avionic equipment.

The primary flight control system retains the reliable, cable-driven design of the DC-9, and its simple, two-position slat system. Improvements to the flight control system include a newly styled pedestal with removable control modules. The most noticeable changes are the elimination of the horizontal stabilizer "suitcase handles," the outflow valve manual control wheel, crossfeed levers, and trim control knobs. Electric trim switches replace the manual aileron and rudder trim knobs. Finally, an all-new, electrically controlled spoiler system with a vernier control handle allows the flight crew to set the speed brakes at any position, from zero to full deployment, without the need for detents or latches.

The control wheels are restyled to improve visibility of the displays. The mechanical "green band" computer has been removed from the pedestal, and the green band function electronically displays on the aircraft configuration display.

The pneumatic and ice protection system has been simplified by the use of a single isolation valve instead of dual crossfeed valves. This allows full-time, simultaneous anti-icing of the wing and horizontal stabilizer leading edge surfaces. The system eliminates the tail and wing de-ice timers and relays, and a back-up function is contained in the pneumatic overheat detection system (PODS).

To improve PODS dispatch reliability, dual-loop sensors replace the bimetallic point sensors used on previous designs. The dual-sensor system achieves excellent fault isolation by providing the specific zone or location of detected leaks. Overheat detection loops for the wing and tail anti-ice system detect a leak or burst duct and automatically shut off the affected system.

The vacuum waste system incorporates a single high-capacity waste tank mounted in the aft cargo area. The tank location allows for positive drainage, and reduces cabin odors by providing single-point servicing near the outflow valve, away from the passenger cabin. The vacuum waste system uses water from the potable water supply, which prevents the formation of blue ice and the corrosion associated with blue water systems.

New, integrally heated potable water hoses prevent freezing at ambient temperatures as low as -40 degrees Fahrenheit (-40 degrees Celsius). However, the hoses are designed to withstand the effects of freezing if the heaters are not activated.

The APU is extremely fuel efficient, and contains an electronic engine controller that monitors and optimizes APU operation. The controller also monitors the APU on the ground for unsupervised operation. The APU inlet has been moved from the bottom to the upper-left side of the airplane. The new location reduces ramp noise levels to meet the most stringent airport noise regulations.

The fuel distribution system is similar to that of the DC-9. A capacitance-type fuel quantity gauging system offers better reliability, and pressure sensors are installed on each fuel pump to aid in troubleshooting as well as improving Master Minimum Equipment List (MMEL) dispatch capabilities.

Optional, modular auxiliary fuel tanks are available in 460-, 730-, 1,010-, and 1,290-gallon (1,741, 2,763, 3,787, and 4,883 L) configurations. The modular design allows the tanks to be removed or reinstalled in one overnight shift.

The 717 nose gear is common to the Douglas twin-jet family. Both the main- and nose-gear designs incorporate the latest corrosion-protection improvements. The gear is fitted with long-life steel brakes that slip onto a set of shear pins, eliminating the multiple-bolt design used on the DC-9. For ease of maintenance, the brakes have quick disconnects on the hydraulic lines and a brake bleed port at the high point on the gear.

A new, in-line 3,000 psi engine-driven hydraulic pump eliminates the 1,500 psi selection switch in the DC-9 cockpit. All hydraulically actuated systems operate at 3,000 psi, eliminating the need for hydraulic step-down pressure reducers. Highly reliable pressure transducers provide hydraulic-pressure indication.

New, high-power, anti-collision lights improve reliability and reduce light-intensity inspection requirements. Long-life, high-intensity quartz halogen lights are installed throughout the service and maintenance locations of the airplane for improved reliability and superior lighting.

A new proximity system is integrated with the CFDS to allow for direct sensor readout during rigging. The system also improves maintenance troubleshooting through fault logging in non-volatile random access memory. A durable, saturated core sensor improves operation and reliability in high-vibration areas.

The BMW/Rolls Royce BR715 engine has a standard static thrust rating of 18,500 lb. Optional thrust ratings of up to 21,000 lb are currently available, and higher thrust ratings will be available in the future.

The engine is electronically controlled (EEC) to provide improved engine life, automated fault reporting, and superior engine condition monitoring capabilities. The EEC eliminates the need for throttle rigging during engine change, and it allows many engine components to be changed and verified without the engine run required on the DC-9.

The engine has a 58-in, durable wide-chord fan resistant to foreign object damage and shares a common core with the BR710. The engine is mounted in a simple, long-duct nacelle design that provides easy maintenance access to components located on the fan case. The inlet and fan cowls are made from aluminum, making them damage tolerant and easy to repair. Finally, the thrust reverser uses a simple, single-pivot door design that is hydraulically actuated.

An airline advisory team worked with the engine design team to develop one of the most maintainable engines in the industry. The newly developed design allowed basic engine maintenance concepts to be applied from the start, such as locating pneumatics on the top of the engine and placing the fuel and oil on the bottom of the engine. Other factors affecting ease of maintenance, such as component accessibility, bore-scope access, access door location, and sight glass visibility, are key to the design. Lower maintenance costs should also result from such efforts as the elimination of safety wire from service points and design for tool access.

The 717 builds on the reliability of the DC-9 to offer enhanced flight operations and improved maintainability, including the BR715 engine, which was desinged to be one of the most maintainable engines in the industry. LCD technology more efficiently presents information in the flight deck, and versatile integrated avionic computers perform the functions of the FMS, central aural warning system, and flight data acquisition system. The focus of system improvement efforts range from air conditioning, interiors, and flight controls to pneumatics, ice protection, water and waste, the APU, fuel, and engines. As the result of an improved design process, the airplane offers improved component accessibility, enhanced ease of maintenance, more flexible maintenance planning, higher dispatch-reliability levels, and lower maintenance costs.

Tom Croslin
Chief Design Engineer
717 Program Office
Douglas Products Division

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