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  • FLIGHT TEST: Boeing 777-300ER - Fast and heavy

FLIGHT TEST: Boeing 777-300ER - Fast and heavy

Boeing has retained the 777's excellent flying qualities with the heavier, more powerful -300ER, while adding range and fuel performance gains

Boeing's original game plan for the 777 family always included longer-haul variants to satisfy an embryonic point-to-point market with massive potential. But 10 years ago, even the keenest visionaries could not have foreseen the sheer size and power of the 777-300ER, the first of two variants developed to attack this growing global network.

The 777-300ER is the largest and most powerful twin-engined aircraft ever developed. In a little over a year's time it will be joined by its stablemate, the even longer-range 777-200LR. Both form the ultimate expressions of Boeing's payload and range growth strategy for the 777 family. Building on successive weight, power and stretch developments, the extension into the longer-range market was entirely dependent on engine growth to an almost unbelievable 115,000lb thrust (512kN).

After several false starts, Boeing defined the -200X/300X pair and held a "winner takes all" engine competition in 1999. General Electric won with the GE90-11X and formal launch took place in February 2000. Boeing and GE projected a potential market of up to 600 "longer-range 777Xs". Five months later, the 300-passenger, 17,200km (9,300nm)-range 777-200X was redubbed the -200LR, while the 365-passenger, 14,250km (originally 13,280km)-range -300X was designated the -300ER.

Development began and the -300ER first flew in February 2003. Now approaching the end of a year-long, two-aircraft flight-test effort, with Boeing on the verge of certificating the 777-300ER in the first quarter of 2004, Flight International was invited to fly the aircraft at Boeing Field in Seattle.

I was accompanied by Boeing captain Suzanna Darcy. External power was connected to the aircraft as we performed the preflight walk-around. In general arrangement, the 777-300ER is nearly identical to the basic -300, with the exception of the 2m-long raked wingtip extensions and the engines. The aircraft has been strengthened to accommodate higher gross weights and there are changes to the landing gear.

The 777-300ER is powered exclusively by General Electric GE90-115B turbofans, each producing 115,300lb (512kN) of thrust at sea level. Large composite blades, with their distinctive wavy leading edges, give the fan section a diameter of 3.25m, larger than the fuselage cross-section of some narrowbody airliners.

Inside story

With its 10 exterior doors, the aircraft could seat nearly 550 passengers in a single-class configuration, but Boeing uses a baseline of 365 passengers in three-class seating for marketing and comparison purposes. The cabin of our aircraft featured flight-test equipment and economy-class seats. The forward portion featured a conceptual advanced cabin design.

The flightdeck is essentially identical to that of the -200/300. Six large liquid-crystal displays are arranged in the now familiar format, with side-by-side primary flight displays (PFD) and navigation displays (ND) for each pilot and two centre stacked multifunction displays (MFD) for the engine information and crew-alerting system. Each ND can also function as an MFD for added versatility and redundancy.

On each side of the centre pedestal is a cursor control device (CCD) - a touchpad, not the trackball used in Dassault's EASy advanced flightdeck. One nice feature: the 777's CCD allows the cursor to be moved directly to the corner of the active display just by touching the corresponding corner of the touchpad.

The overhead panel employs mainly flush pushbuttons, with system schematics and associated switches logically arranged. The 777 employs a dark panel philosophy. A limited number of critical circuit breakers are located aft of the overhead panel. A glareshield-mounted flight-guidance control panel and three centre-pedestal control display units (CDU) round out the 777's flightdeck.

Stretching the 777's fuselage 10.1m (33ft) for the -300 and -300ER variants was challenging. The main landing-gear geometry was not changed for the- 300 and the additional 4.8m of fuselage aft of the wing limited the body angle attainable on take-off rotation. While this no doubt degraded the runway performance of the -300, it still meets all operational requirements.

The heavier -300ER was a different matter, as a slightly higher take-off attitude was needed to meet operational requirements. The length of the main gear had to be extended, yet it still had to retract into the existing wheel wells. Boeing devised a semi-levered arrangement for the main gear. A hydraulic strut connects the forward part of the wheel truck to the top of the vertical gear strut. On rotation, the diagonal strut locks in place to keep the gear truck perpendicular to the vertical strut. Instead of rotating about the centre axle, the aircraft now rotates about the aft axle, increasing the apparent height of main gear by around 0.3m.

Tailstrike danger

As with the stretched Airbus A340-600, tailstrikes are possible, so the control laws of the fly-by-wire 777-300ER in the pitch axis incorporate a tailstrike protection feature. This is available in the normal mode of the fly-by-wire control system and uses up to 10° nose-down elevator to prevent a tailstrike. Flight-test results show the semi-levered gear and tailstrike protection, along with minor improvements to the brakes, have combined to reduce the -300ER's predicted take-off field length by 305m.

Darcy fired up the tail-mounted auxiliary power unit (APU) in preparation for engine start. On the ground, the APU's primary start mode is via a dedicated battery. In flight it will try to start using pneumatic bleed air if available. The engines were started one at a time using the auto-start feature of the full-authority digital engine controls. Each engine reached an idle N2 of about 69% in less than 1min, with exhaust gas temperature peaking at around 500°C (930¡F) - maximum is 750°C. Post-start and pre-taxi checks were easily accomplished.

The 777-300ER has two cameras mounted in the horizontal tail and one in the ventral fuselage, designed to assist when taxiing this long aircraft on narrow tarmac. Darcy put the camera display up on the lower centre MFD before starting the taxi. The display has three windows, one for each camera. The two tail-mounted cameras clearly showed each engine and respective main landing-gear wheels, as well as about half the wing. The ventral camera showed the nose gear and lower portion of the forward fuselage.

Ground manoeuvrability of all 777s is enhanced by the steerable aft axle (of three) on each main landing-gear truck. Taxiing the -300ER was not unlike taxiing the shorter -200, but the camera view of the nose gear allowed the aircraft to be kept on centreline. Flaps were set to "5" in preparation for a maximum power take-off on runway 31L.

Once cleared for take-off, I advanced the throttles about halfway forward and allowed N1 to stabilise before hitting the throttle-mounted take-off/go-around switch. The autothrottles (left and right) advanced the throttles and established an N1 of 101.9%. With 59,060kg (130,200lb) of fuel, the aircraft's gross weight was only 220,720kg, well below the maximum take-off weight of 334,550kg. Our operational empty weight of 161,660kg was significantly lower than the projected 168,560kg in airline configuration.

Acceleration was quite brisk, and Darcy called "rotate" at 143kt indicated airspeed (265km/h). I initially pulled aft with 5kg of force, increasing to 12kg until a nose-high attitude of 10° was obtained. Boeing recommends an aft yoke pull to establish a rotation rate of 2.5°/s until the aircraft lifts off. I generated a maximum pitch rate of about 5°/s in the latter part of the rotation manoeuvre, but even this aggressive pull did not trigger the tailstrike protection.

Guide climb

Twenty-eight seconds after brake release and a ground run of 1,000m, the 777 lifted off the runway and I established a 15° climb attitude. Pitch trim rapidly relieved yoke forces as gear and flaps were retracted during acceleration to the initial 250kt climb speed.

At 8,000ft above mean sea level, I engaged the autopilot in heading-select roll mode and vertical-navigation (VNAV) pitch mode. Passing 10,000ft, the autopilot lowered the nose and accelerated the aircraft to 320kt. VNAV mode held 320kt until a climb Mach of 0.82 was captured. The autothrottles kept both engines at the maximum climb N1, and the aircraft passed FL310 (31,000ft) just 10min 46s after brake release.

Boeing projects reaching FL310 about 23min after brake release at a take-off weight of 351,080kg, and says an A340-600 weighing 376,000kg would require 11min longer and be 140km farther down range. The ability to reach cruise altitude rapidly is appreciated by operators as it reduces the risk that the aircraft may be stuck at a lower than optimal initial oceanic cruise altitude.

The 777-300ER's climb capability is the direct consequence of its excess power. For regulatory reasons alone a twinjet has a higher thrust-to-weight ratio with all engines operating than a four-engined aircraft. A two-engined aircraft must be able to establish a climb gradient of 2.4% in the event of an engine failure on take-off, while a four-engined aircraft must maintain a slightly higher gradient of 3%. The 777-300ER's two engines put out more thrust than the A340-600's four at any given take-off weight, and are sized to account for an engine failure and loss of 50% thrust compared to only a 25% loss for the quad-jet. The numbers bear this out, as at maximum take-off weight the 777-300ER's thrust-to-weight ratio of 0.304 is about 13% higher than the A340-600's 0.27.

The autopilot levelled the aircraft out at FL350, but was then disengaged for some 60° angle-of-bank steep turns at 290kt/M0.84. For bank angles up to 30°, the flight control system (FCS) automatically puts in an up-elevator command to maintain level flight. Passing 35° bank, the FCS provides an opposing roll force on the yoke to reduce the bank angle. This force is easily overcome, and the FCS would not prevent the pilot performing a 360° aileron roll. Releasing the yoke with bank angles greater than 35° will cause the FCS to establish a 30° bank. I found the 777 quite responsive and predictable in roll during these manoeuvres.

The autothrottles were then engaged for a series of cruise performance tests. One strength of the 777 family is its ability to comfortably cruise faster than the competition. The first point was at the 777's published cruise speed of M0.84, slightly quicker than the A340-600's M0.83. Maintaining a true airspeed of 472kt, the 216,370kg aircraft had a total fuel flow of 6,790kg/h (14,960lb/h). At M0.87/506kt, faster than the A340-600's M0.86 maximum Mach number (MMO), total fuel flow was 8,890kg. At this high Mach the flightdeck of the 777 was remarkably quiet, subjectively much quieter than a 747's.

Next I disconnected the autopilot and autothrottles and lowered the nose to accelerate to the M0.89 MMO. The autoflight system will not exceed MMO/VMO, but when flown manually the FCS will not stop the aircraft from being pushed outside published limits. Sharp control inputs in each axis showed the aircraft to be stable. Passing FL290, the VMO of 330kt (displayed as equivalent airspeed for the first time on the 777-300ER) was captured. Pulling the speedbrake lever full aft caused the nose to pitch up 3° from the trimmed condition. A slight airframe buffet was felt and about 4.5kg of forward yoke was required to maintain the desired pitch attitude for this rapid descent.

Descent was continued down to 15,000ft where I would be able to sample slow-speed handling qualities. The 777 has several features designed to prevent inadvertent entry into a stall. If the autothrottles are engaged they will advance power as the aircraft slows to maintain minimum manoeuvring speed for the configuration. If the autothrottles are armed, but not engaged, they will "wake up" as the aircraft slows to the minimum manoeuvring speed and keep it from slowing further.

Slow-speed handling

With the autopilot and autothrottles disengaged, the first approach to stall was performed at idle power in a clean configuration. I slowed the 212,740kg aircraft at 1kt/s and stopped trimming in the pitch axis at the clean manoeuvring speed of 218kt. An amber band was displayed at 197kt, indicating the minimum manoeuvring speed. As the aircraft slowed through that speed an amber pitch limit indicator (PLI) was displayed above the attitude director indicator's aircraft symbol, graphically showing the pitch attitude for stick-shaker activation.

At 169kt, the stick shaker activated as the PLI touched the aircraft symbol. Descending to maintain shaker speed, I found aircraft response to control inputs in all three axes to be good. Recovery to normal flight was achieved by advancing the power and relaxing yoke backpressure.

A landing-configuration approach to stall, gear down and flaps "30", was performed next. VREF was about 138kt, with the amber band displayed at 123kt. Stick-shaker activation was at 109kt, a seemingly low speed for such a large aircraft. As with the clean stall, control effectiveness was quite good in all three axes. I advanced power on the engines to a mid-range position and used the PLI as a guide to accelerate and climb out of the stall.

After cleaning the aircraft up, a descent was established as air traffic control vectored us to fly an instrument landing system approach to runway 32R at Moses Lake airport in eastern Washington. The 777 has a thrust asymmetry compensation (TAC) system available in the normal flight-control mode. If the system senses an asymmetric thrust condition it will command rudder to offset the yawing.

During the descent Darcy retarded the left throttle to idle to simulate an engine failure. To cue the pilot to the thrust asymmetry, the TAC allows a slight yaw and roll to develop before applying the corrective rudder. The left autothrottle was disengaged, allowing the right unit to maintain the desired airspeed while the TAC maintained co-ordinated flight.

I engaged the autopilot on the downwind leg and slowed the 777 to 190kt with the flaps set to "5". On a dogleg to final, I armed the approach mode of the autopilot to allow it to capture the localiser and glideslope. Gear was extended and flaps set to "20" as the aircraft slowed to a target speed of 160kt. During the speed and configuration changes the TAC did a superb job of countering yawing motions. The only obvious clue that we were flying on one engine was that the autothrottle was only moving the right throttle. The autopilot smoothly tracked localiser and glideslope.

Passing around 1,500ft radar altitude, "Land 3" was annunciated on the PFD, indicating aircraft systems were capable of performing an automatic landing. Stabilised on final approach, the right engine was at 55% N1 and the TAC held about 3° right rudder. At 50ft, the aircraft began the flare manoeuvre, and at 25ft the autothrottle began retarding the right throttle to idle. The TAC centred rudder trim as power was reduced and the aircraft touched down on the runway centreline about 500m from the approach end. The autopilot gently lowered the nose to the runway and tracked centreline as the speed brakes deployed and wheel brakes were automatically actuated.

Slowing through 50kt, I disengaged the autopilot and autothrottle to manually taxi the aircraft. Taxiing to the end of the runway, Honeywell's developmental runway awareness and advisory system (RAAS) called out thousands of feet remaining. Based on the company's enhanced ground-proximity warning system, the RAAS accurately gave the remaining runway distance.

At the departure end of the runway a left-hand 270° turn was accomplished to face runway 14L while we awaited clearance for our return flight to Boeing Field. Once cleared by air traffic control, I advanced the power to line up on the runway. Before entering the runway, the RAAS called out "approaching runway 14L". On the runway it called out "on runway 14L". The RAAS call-outs seemed redundant, given the good weather conditions and familiar location, but several recent accidents may have been prevented had it been available.

Tailstrike avoided

The take-off from Moses Lake would be at flaps "20" and maximum thrust. For this take-off we would try to intentionally trigger the tailstrike protection system by aggressively rotating 5kt before the recommended rotation speed. At 123kt I pulled aft and generated a peak pitch rate of 5.25°/s, twice the recommended rate. The tailstrike protection system noted the decreasing tailskid clearance and put in 9° of down elevator to arrest the motion. This kept the tailskid 0.66m above the runway but was transparent in the cockpit, as rotation and lift-off felt normal.

The 777-300ER's vertical stabiliser and rudder are the same size as the -200's, yet each engine puts out significantly more thrust than those on the shorter -200 models, roughly 115,000lb versus 90,000lb. Boeing increased rudder authority by enlarging the rudder power control units. During the climbout at 148kt (V2 +5kt), with gear and flaps still extended, Darcy retarded the left throttle to idle. With the TAC off, it took two-thirds of the available rudder and 40kg of force to maintain wings level steady-heading flight, well below regulatory maximums. The fact that the more powerful rudder and longer moment arm afforded by the lengthened fuselage were sufficient to counteract the increased asymmetric thrust of the GE90-115B engines no doubt simplified development of the -300ER. Satisfied with the -300ER's engine-out handling qualities, gear and flaps were retracted for a two-engine climb to FL200 and return to Boeing Field.

During the return leg, I was able to familiarise myself with the Jeppesen electronic flight bag (EFB). KLM and Pakistan International Airlines have ordered the EFB for their new 777s, but it is retrofittable to all 777s. EFB content can be tailored to each user's specifications and is a big step towards a paperless cockpit. In addition to providing accurate real-time runway performance calculations, the EFB can store and present a multitude of items. Navigation charts, terminal arrival and departure procedures as well as airport diagrams are items most pilots will appreciate.

Due to certification concerns the EFB will not display current aircraft position on navigation charts while airborne, although it does display ground position on airport diagrams. The approach chart for runway 31L, the planned approach, was displayed on the EFB's 150 x 205mm LCD. Slightly larger than the comparable paper chart, I found it easy to read even in the changing light conditions nearing dusk.

The approach to Boeing Field was a hand-flown ILS with flaps set to "30", the full down position. The flight director bars allowed me to easily track both the localiser and glideslope, while the autothrottle maintained the 136kt target speed for the 206,840kg aircraft. Roll and pitch response on final were crisp, displaying none of the inertia one would expect of aircraft nearly as large as a Classic 747.

As would be done in the shorter 777-200, I disengaged the autothrottles and started the flare manoeuvre at 30ft radar altitude. The aircraft gently touched down 600m from the approach end and reverse thrust and moderate wheel braking were used to slow to taxi speed. During the taxi back to the ramp, I again found the cameras useful in keeping the nosewheel exactly on the taxiway centreline. Shutdown and post-flight procedures were straightforward and easily accomplished.

Aircraft costs are strongly linked to the number of engines, and expanded ETOPS authorisations allow the twin-engined 777-300ER to operate efficiently on globe-spanning routes. In long-range operations, Boeing says, the 777-300ER will use 22% less fuel per passenger than the A340-600.

I have flown both aircraft. From a pilot's point of view, both are well suited for their designed roles. Each of these fly-by-wire aircraft has excellent flying qualities, remarkable given their large size.

Boeing has successfully developed a very large aircraft that - despite major thrust and weight increases - appears to seamlessly share the same satisfying handling characteristics as its earlier siblings. Added to this, the company has also uncovered additional range and fuel consumption performance margins in flight tests that seem likely to kick-start new sales and help guarantee a long and fruitful life for the -300ER branch of the 777 family tree.

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