Boeing's 777-300ER, the ultimate stretched twin, will be heavier, more powerful and able to fly for longer than its siblings

Boeing's latest 777 derivative, the -300ER, is poised to start a year-long flight test and certification effort, with a first delivery to Air France due early next year.

Despite the new paint scheme on the first 777-300ER, a casual observer could be forgiven for experiencing a feeling of déja vu. Apart from some minor details, the new aircraft is, externally, virtually identical to the -300 that first flew in October 1997. Yet beneath the surface, it is a different story - and the team has its work cut out to test, verify, demonstrate and certificate this vastly more capable variant.

Compared to the original -200 model, the -300ER's maximum take-off weight is around 90,800kg (200,000lb) greater. It has a total engine thrust capability of over 230,000lb (1,024kN), roughly equal to the thrust of three of the 777-200 engines. The -ER also has a maximum take-off weight of around 60,000lb more than the -300, extending its range over the standard model by 2,410km (1,300nm) to 13,430km, and enabling it to carry an extra 19,700kg of cargo.

The major difference between the -300ER and its predecessor is the 115,000lb-thrust General Electric GE90-115B turbofan, which is due for US FAR 33 certification around the time of its first flight. The engine, the largest turbofan ever developed, gained exclusivity on the longer-range 777-200LR/300ER derivatives after a three-way contest in July 1999. Despite the larger, 3.25m (10.65ft) fan diameter of the -115B, the engine appears proportionately similar to its 777-200 predecessors.

Another key development is the pair of 2m-long tapered wingtip extensions, which increase the span to 64.8m - or around the same as a 747-400. Made mostly from composites by Korean Air Lines' Busan-based Aerospace division, the new devices are modelled on the tips introduced on the 767-400ER and mate to the wing via wingbox extensions also built by Korean Air. Boeing expects the tips to generate a 2% fuel efficiency improvement, producing savings of around 591,000kg in fuel and $140,000 a year per aircraft.

Modified main gear

Another change requiring closer inspection is the modified semi-levered main gear that was developed, along with the aerodynamic and engine changes, to keep take-off performance within limits at maximum gross weights.

The main visible difference to the gear is a large actuator that projects forward from the main undercarriage post to the front axle. As the aircraft rotates, the actuator holds the front part of the truck down, allowing the aircraft to pivot about the aft main wheel set. This provides additional rotation angle, which reduces the required take-off speed and distance.

All the external changes, and the myriad modifications to the interior, have been made to accommodate the much higher 340,195kg gross weight of the longer-range twins. The aircraft is configured with heavier-gauge fuselage and wing skins, revised and updated systems, and extensive new interior features such as upper-lobe crew rests, all of which will form the test programme's focus. This will consist of several phases, the first of which has been under way since October, covering service-ready, maintenance and system check-out issues.

First flight therefore slots into what is already a mature test and validation effort. To date, this has encompassed bench tests of the second-generation Honeywell aircraft information management system, Honeywell air supply and cabin pressure controller, a fifth-generation BAE Systems electronic engine control, Smiths Aerospace electrical load management system, a brake test rig and several rigs for the undercarriage, including ones for landing gear door actuation, as well as the semi-levered gear actuator. Early validation of the gear has also included flight tests of a modified 777-300 at Edwards AFB, California, as well as a high-lift dynamic loads survey. New BAE Systems primary flight-control computers were also tested on a standard -300 production aircraft in late November, while tests of the GE90-115B were conducted by GE using its own 747-100 testbed.

Integration testing

When it came to complex pre-flight tests of new integrated systems, Boeing realised it had something of a shortfall since its systems integration laboratory, a purpose-built site developed to support the 777 programme in the 1990s, had been dismantled.

Joe Kranak, 777 test and validation chief engineer, says: "Because we had significant system changes, we needed to run additional integration tests, so we have established some integration testing in the cab [engineering flightdeck simulator], and the flight emulation test system [FETS]."

He adds: "The FETS is a portable simulator which enables us basically to fool the aircraft into believing it is in flight - yet without ever leaving the ground. We will use it to conduct a Boeing initial check [B-1] profile flight while the aircraft is still in the hangar."

Then comes the real thing under the command of 777 chief pilot Frank Santoni, who says he will "fly the 777-300ER for 5h on its first flight as a requirement to land at Boeing Field. During this flight, we will conduct a thorough check of the aircraft, including all of the B-1 profile checks, with additional tests identified to us by engineering." He adds, joking, that his "vision is to land at Boeing Field and, if allowed, be able to put a full load of passengers onboard and start revenue service that day."

Santoni's aircraft, WD501, is the first of two test 777-300ERs in the programme. A third had been planned, but following the restructuring of the longer-range twin development effort in the wake of the 11 September terrorist attacks - including the temporary shelving of the -200LR - it was decided to stretch the -300ER test programme over two airframes.

Together with WD502 - due to join the programme in February - the two aircraft will between them be instrumented to take 15,924 digital databus and 1,709 analogue measurements, as well as data from 134 Arinc buses. Around 30% of the main analogue data channels will be associated with tests of the nose and main gear, while a great proportion of the remaining test instrumentation is connected to the engines, structure and systems.

The interior of the test aircraft has the look and feel of earlier prototypes, but with some notable differences. Along with the usual aft-mounted winch to reel in the static pressure trailing cone, the cabin contains water barrels that can simulate different loads. Pumps transfer water between the forward and aft barrels and vice-versa to produce varying centre-of-gravity conditions in flight.

Weight simulation

For the first time during the extended-range twin operations (ETOPS) portion of the test effort, the barrels will be fitted with heating elements to enable the water to be used as a heat soak for the excess electrical load produced by the onboard generators during some of the heavy-duty test conditions.

The cabin also houses the fourth-generation airborne data acquisition and monitor system (ADAMS), which was laid out and checked in a data system laboratory at Boeing Field before installation in the aircraft at Everett, Washington. ADAMS also incorporates new engineering situational awareness and visualisation tools derived from recent military test programmes such as the X-32 and X-45.

The first flight kicks-off a 12-month effort expected to cover around 1,600h of flight tests and around 1,000h of ground tests for both aircraft combined. Most of the hours will be amassed by WD501 which will immediately be used to clear the initial flutter envelope. Boeing hopes to obtain type inspection authorisation by the end of February, by which time brake tuning and systems tests will be well under way. By March, WD501 is due to begin almost two months of aerodynamic performance test work, most of which will be based at Edwards AFB.

In April, assuming all goes well in the aerodynamic tests, the aircraft will travel between California and New Mexico undergoing brake performance test work on the long runways at Edwards and Roswell. Aircraft test work for WD501 will be wrapped up with a final phase, due to last around three months, covering stability and controls.

Preflight and safety review work on WD502 started around December and, following first flight sometime in February, the aircraft is due to launch straight into cruise performance work. By March, the aircraft is due to begin major engine testing and nacelle cooling trials before spending the final three months on systems tests, community noise evaluation and more stability and controls work.

Both aircraft are due to complete aircraft test work within a few weeks of one another around the end of August and early September, before moving on to the last and final phase covering ETOPS clearance and final certification in January 2004. Although not as complex as the original 777 test effort, the -300ERprogramme contains unique challenges and will break new ground for big twin development.

Source: Flight International