Michael Gerzanics/LONG BEACH
Boeing's 717 is poised to be the newest aircraft to enter the much anticipated 100-seat airliner market. With joint US and European certification due in September, Boeing hopes to capture the lion's share of a projected 2,600-aircraft market through to 2017. Airbus Industrie's entry into the 100-seat arena with its A318, however, has made attainment of this goal far from certain.
Launched in October 1995 by McDonnell Douglas as the MD-95, the 717 has faced several major programme hurdles during its development. The first and perhaps most challenging was the near demise of ValuJet, its initial launch customer. But ValuJet lives on as AirTran Airways, and its 50 firm orders and 50 options remain on Boeing's books.
The second was the merger of McDonnell Douglas and Boeing in 1997. Boeing already had a 100-seater in its product line, the 737-600, and industry analysts were sceptical that the company would offer two seemingly similar products. Boeing rallied to the cause of the MD-95, however, which it re-named the 717. The aircraft therefore became a symbol of the "new Boeing" and is being marketed as a low-cost airliner optimised for the short-haul market.
Since the 717's first flight in September, four aircraft have completed 1,200h of a projected 1,700h flight test programme. Over 90% of the developmental flight testing has been accomplished so far, and 50% of the combined US Federal Aviation Administration/European Joint Aviation Authorities certification points have been demonstrated. Flight International was given the opportunity to fly the aircraft at Boeing's Long Beach, California, facility.
The goal of the 717 programme was to develop a 100-seat airliner optimised to provide the lowest total trip cost when operated at high frequency over about 500-900km stage lengths. Some would contend that the 717 is nothing more than an updated DC-9-30, but this is not the case. While justifiably proud of the aircraft's heritage, Boeing takes great pains to highlight the many differences and improvements the 717 represents over the DC-9. The fuselage and wing are carried over from the DC-9-30, but almost everything else has been changed.
Using the DC-9-30's existing fuselage and wing design for the 717 has resulted in major development and certification savings which are reflected in the aircraft's $31.5 million 1999 list price. The fuselage, manufactured by Alenia of Italy, is a three-frame stretch of the DC-9-30's. Added forward of the wing, the frames allow for an extra row of seats while also increasing the centre of gravity (CG) range. The production wing will be manufactured by South Korea's Hyundai Space & Aircraft, and is essentially unchanged from the baseline DC-9-30 design. In addition to obvious production savings, costs are further reduced when fatigue-life certification expenses are considered.
The high-bypass-ratio BMW Rolls-Royce BR715 turbofan engines are the biggest external difference between the 717 and its DC-9- series predecessors. The BR715 shares its core with the BR710, used on the Bombardier Global Express and Gulfstream V business jets. Its 1.47m (58in)-diameter wide-chord fan and full-authority digital electronic control allow the BR715 to produce 18,500lb thrust (82kN) in standard form, with an optional maximum of 21,000lb. AirTran has bought the pin-selectable 21,000lb option for its initial 50 aircraft.
While inherently fuel efficient, the BR715's fuel flows have been running at about 1.5% less than predicted in flight test. Noise and emissions levels are all well below current and projected regulatory limits.
From the pilot's perspective, the biggest changes from the DC-9 are in the cockpit. Proven MD-11 technologies and designs were adapted to the 717 during its development. The new avionics are supplied by Honeywell. Six 200 x 200mm liquid-crystal displays (LCDs) comprising the forward instrument panel are powered by two redundant integrated avionics computers. Typically, two LCDs serve as primary flight displays (PFDs), two as navigation displays, and two as primary and secondary engine and alert displays (EADs).
The automatic flight control system, incorporating both autopilot and autothrottles, is controlled through a glareshield-mounted control panel. The flight management system (FMS), programmed with aircraft performance information as well as navigation and airport data, is controlled by two pedestal-mounted multifunction control and display units. The result is a clutter-free cockpit that looks and feels as up to date as that of Boeing's larger and more expensive 777.
Before flying the 717, I spent some time in an MD-11 fixed-base simulator with Tim Dineen, deputy chief experimental test pilot. I was able to familiarise myself with the operation of the autoflight and flight management systems. Although developed from those in the MD-11, the 717's systems are similar to those on other Boeing aircraft. While there are some differences, any pilot moving from another "glass-cockpit" aircraft would have little difficulty in mastering their operation.
I was able to fly the first production 717-200, N717XD, with 21,000lb-thrust BR715 engines. Painted in AirTran colours, "P-1" has been used to develop cabin interiors and sound dampening. Zero fuel weight of the aircraft was 31,600kg (69,700lb). With 4,900kg of Jet-A fuel, the aircraft's take-off weight would be 36,500kg, well under its maximum of 54,900kg.
After a thorough preflight briefing, Dineen and I walked around the aircraft at Long Beach. Even though the Sundstrand APS2100 auxiliary power unit (APU) was running, we were able to carry on a normal conversation as he pointed out some of the 717's features. All cargo doors are accessible from ramp level without the use of stands or loaders. The preflight was straightforward and accomplished in minutes.
We entered the aircraft via its self-contained forward airstair. Ralph Luczak, Boeing's 717 project pilot, took the right seat. Dineen took the jumpseat between the pilot seats, while flight test engineer Brett Burgeles rode in the passenger cabin. As I settled into the left seat, I noted there was ample room to stow my flight briefcase to my left. The 16g seat, with adjustable lumbar support, was comfortable, an important fatigue-reducing feature in an aircraft designed for high-frequency operations.
The cockpit overhead panel contains control panels for the aircraft's major systems: hydraulic, electrical, pneumatic and fuel. Panel layout is straightforward and logical for each system. In general, when a system is configured for normal operations, all switches are put forward. Exterior and cockpit light switches are on the overhead panel.
Field of view
Field of view out of the cockpit's nine windows was quite good. The autoflight system's glareshield-mounted control panel was easily accessible from either pilot seat. Mounted on the centre pedestal, the two throttles and thrust- reverser levers fell easily to hand. In a testament to simplicity, the fuel crossfeed control lever is located to the right of the throttle quadrant. Unlike other Boeing aircraft, this long-throw lever moves a cable that physically opens and closes the crossfeed valve.
With clearance from ground personnel, both engines were started with bleed air from the APU. While the 717 has an auto-start capability, we were required to motor/cool the engines for 30s before manually starting them. The 30s motoring period extends engine life, and is only required during a certain window following a recent shutdown. The production auto-start system will incorporate this requirement in its control logic. During the start sequence each engine reached a peak turbine gas temperature of 550ºC, well short of the 700ºC limit.
After the simple post-start procedures were accomplished, Luczak requested taxi clearance to Long Beach's runway 30. Little more than idle thrust was required to get the 717 rolling. Once moving, the relatively light aircraft easily accelerated to 25kt (45km/h) and I used the robust steel brakes to control taxi speed. The thrust reversers could have been used to slow taxi speed, as they are authorised for ground operations, including gate power-back. Tiller-controlled nosewheel steering (NWS), providing +/-82º of articulation, was required to negotiate several 90º turns en route to the runway. Rudder-pedal NWS, providing +/-17¼º of articulation, allowed me to track accurately straight taxiway centrelines.
Take-off CG was 22.7%, and the flaps were set to 13º. In addition to this preset take-off flap position, the 717 has a "Dial-a-Flap" selector for settings of less than 13º. The Dial-a-Flap feature allows operators to select the optimum flap position for runway and gross weight conditions. The pre-take-off checklist was completed, read off of a laminated card as there is no electronic one, and air traffic control cleared us on to the runway.
Once aligned on the runway centreline, I stopped the aircraft and armed the autothrottles. The winds were calm when ATC cleared "Boeing 4" for take-off. I simultaneously released the brakes and pushed the throttles forward until the autothrottles engaged and moved them to the maximum take-off exhaust pressure ratio: 1.53 for this 19ºC day. The runway centreline was tracked with rudder pedals only. Acceleration was brisk and the 117kt indicated airspeed (IAS) decision speed (V1) was reached in seconds. Rotation, initiated at 125kt, required moderate control force to attain a target pitch rate of 2.5º/s until a 12º nose-high attitude was obtained. The aircraft lifted off 730m (2,400ft) from brake release and quickly accelerated through the 132kt take-off safety speed (V2).
After the landing gear was retracted, I released the yoke to determine the aircraft's trim speed. The aircraft climbed out at 165kt, a speed safely above V2. Next, I followed the pitch guidance provided by the split-cue flight director on the PFD. Climb thrust was selected at 1,500ft above ground level (AGL). At 3,000ft, the nose was lowered and the flaps immediately retracted. As the aircraft accelerated towards 250kt, the leading edge slats were retracted. During all configuration changes control force changes were light. Continuing to climb at 250kt, we initiated a southerly turn towards our work area.
I engaged the autopilot with a button on the glareshield panel, the autothrottles having been engaged for take-off. The flight mode annunciator on the primary flight displays clearly showed the autopilot and autothrottles were flying the aircraft, allowing me to devote my attention to looking out for other aircraft.
The FMS generated an economic climb profile which held 276kt IAS until Mach 0.75 was intercepted and held at 31,000ft. Vertical speed throughout the climb was 3,000ft/min (15m/s) or above. ATC gave us several unwelcome intermediate level-offs, preventing an expeditious climb to our cruise altitude of 35,000ft. Without such interruptions, we would have reached 35,000ft 12min after take-off and burned only 860kg (1,900lb) of fuel.
Once level at 35,000ft, the aircraft was hand flown at the FMS economic cruise speed of M0.74/249kt. At a gross weight of 35,150kg, total fuel flow was 1,770kg an hour. Several 30º bank-to-bank turns were accomplished. The manual tab-flown aileron forces were smooth and linear, requiring no rudder to co-ordinate. Although we were just 2,000ft below the aircraft's maximum certified ceiling of 37,000ft, no buffet was felt during these manoeuvres.
Since this short haul aircraft will spend the majority of its time cruising at 30,000ft and below, I used the autoflight system to descend and level off at 30,000ft. Economic cruise at this altitude was M0.7/262kt, and total fuel flow was 1,700kg an hour. The cockpit was fairly quiet during cruise and we could hold a normal conversation without difficulty.
To initiate the descent for our return, I fully deployed the speedbrakes at 260kt. A slight heave was felt as they deployed, followed by a gentle nose drop. There was light airframe buffet and about 4.5kg of aft yoke force was required to hold the nose in the level flight attitude. Retracting the speedbrakes caused a slight, easily countered, pitch up.
As we descended, I slowed to 220kt and excited Dutch roll with a gentle rudder doublet. With the yaw damper off it was lightly damped at a frequency of one oscillation every 2s (0.5Hz). With the yaw damper on it was deadbeat, fully damping out in one cycle. In our descent at 220kt, Luczak turned off the rudder boost. Lacking hydraulic pressure from either of the two available systems, the rudder's control tab unlocked and it was flown manually with the rudder pedals. Control forces were very heavy, but acceptable for this compound failure situation.
I levelled the aircraft off at 11,000ft and extended the full-span leading-edge slats, leaving the trailing-edge flaps retracted as we slowed through 200kt. This "0/EXT" (0º flap extension/extended slat position) configuration is typically used in the terminal area on approach. One safety feature offered by the autothrottles is low-speed protection. At 5kt IAS below minimum speed, even if not engaged, the autothrottles wake up and advance to maintain a safe speed.
Luczak held the throttles at idle to override the autothrottle speed protection at 124kt IAS, and I slowed the 0gross-weight aircraft at a rate of 1kt/s. The stick shaker activated at 111kt with no perceptible buffet or wing rock. Recovery was initiated by releasing back pressure on the yoke and advancing the throttles. Had the pilot ignored the stick shaker, an aural warning would have sounded, followed by activation of a stick pusher to lower the nose forcibly. Throughout the approach to stall and subsequent recovery, the aircraft responded predictably to all control inputs, an admirable trait, to say the least.
ILS recovery
Recovery to Long Beach was via ATC vectors to an instrument landing system (ILS) approach. Luczak simulated an engine failure by retarding the number one throttle to idle at 3,000ft. At 155kt, still in the 0/EXT configuration, about 14kg of rudder force was required to counter the asymmetric thrust. The electrically activated rudder trim easily trimmed out this force. One minor annoyance was the lack of aileron and rudder trim-position indicators on the pedestal. While they can be presented on the secondary EAD, I would prefer to have them visible at all times.
While level at 3,000ft on a dogleg heading to intercept the ILS localiser course to runway 30, the flaps were extended to 18º and the aircraft slowed to 130kt. The resultant ballooning was easily countered with forward yoke pressure. I manually followed the flight director's guidance as it smoothly intercepted and tracked the localiser course. As we approached the ILS glideslope one dot high, the landing gear was lowered and flaps extended to their landing position of 25º. Final approach was flown at 130kt, with the flight director providing excellent localiser and glideslope guidance. At 500ft AGL, I had Luczak centre the rudder trim so I could get a better feel for the forces required on a single-engine final approach and landing.
The speedbrakes' automatic deployment on touchdown caused no pitch-up, a welcome change from the DC-10, which does so quite noticeably. With the nosewheel still in the air, both thrust-reverse levers were raised to a mid position. The clamshell bucket thrust reversers, however, opened only after the nosewheel was lowered to the runway. Rudder pedal nosewheel steering was sufficient to track the runway centreline on roll-out. While the 717 does have an anti-skid braking system, it was not exercised on this flight.
APU start required only a single switch throw on the overhead panel. After a 3min cool-down period, both engines were shut down. Aircraft electrical power automatically switched to the APU as the engine-driven generators dropped off line. We had flown for 1.3h and burned 2,700kg of fuel.
The 717 had shown itself to be a delightful aircraft to fly. Its modern cockpit, fuel-efficient engines and proven airframe appear well suited to the high frequency short haul market. While only 115 firm orders have been booked to date, Boeing is studying field performance improvements as well as both shrink and stretch versions to broaden the aircraft's market appeal.
Source: Flight International
