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BOEING 777: THE MEGA-TWIN

The 777 already is one Boeing's most successful products. Initially the giant twin-jet airliner was seen to fill a niche between the 767 and the 747, serving as a replacement for the ageing McDonnell Douglas DC-10 and Lockheed L-1011 Tristars on transcontinental routes. Three years after going into service with United Airlines, the twin-engine airliner has developed into a fierce competitor to the Airbus A340 widebody family.

With 392 orders in the books (as of 30 June 1998) the 777 order log is already double as thick as that of the former competitor MD-11 (total of 195). Following Boeing's merger with McDonnell Douglas the end of the MD-11 production has already been decided on.

At the beginning of the design phase for the 777 in 1989, Boeing considered a stretch of the existing 767 to gain a little more capacity and range. However, after including potential customers in the thought process it became clear very fast that there was a need for an entire new aircraft, positioned-between the 767-300 and the 747-400.

As thrust requirement for the basic version, the engineers came up with 160000 lbs. After evaluating all options, Boeing decided to go ahead with a twin-engine concept mainly due to the expected lower operating costs.

The engine manufacturers Pratt & Whitney (PW4000), General Electric (GE90) and Rolls-Royce (Trent 800) each developed engines for the new airliner with thrust ranging from 330 to 373 kN (74000 to 84000 lbs.). The external dimensions of the new engines also reached XXL format: The engine nacelles have a similar diameter to the Boeing 737's fuselage.

Following the official program launch Boeing accomplished an extremely fast development and certification phase. The aircraft first flew in June of 1994. Under the motto "working together" Boeing called in permanent advisory teams from four customer airlines, among them United and British Airways. One of the main tools in designing the 777 was Dassault/IBM's CATIA computer aided design software. Furthermore, Boeing invested $370 million in an integrated test laboratory which allowed the engineers to actually test the hardware before it went into the aircraft.

According to Boeing, the 777 was designed from "inside to out", beginning with the fuselage. It has a circular cross section and its main cabin offers room for up to ten seats in one row. The basic 777-200 version can carry up to 440 passengers in a single-class operation. The stretched -300 can even carry 550 people. With its large overhead bins and an sophisticated in-flight entertainment system, launch customer United praised the aircraft as being the most passenger-friendly aircraft. However, the passengers sitting next to each other in a five-seat row in between the two aisles may not agree with that.

The two-crew cockpit joins elements of the 767 and 747. The instrument panel with its six 20 by 20 cm displays from the Honeywell avionics look similar to the 747 instrument panel lay-out. The overhead panel and the Pedestal are coming from the 767 design. Two conventional control columns are linked to the fly-by-wire flight control system - a first for a Boeing airliner.

The 777 wings are based on a 767 wing box and have a span of 60,93 m. Each of the two main gear struts is sitting on a three-axle wheel assembly with two wheels each. The aft axle of each main gear can be steered +/- 8 degrees for a better ground handling and less tire wear.

The stretched 777-300 also features an ground manoeuvre camera system which is installed underneath the belly and in the vertical tail of the aircraft.

In February of 1997, Boeing delivered the first 777-200IGW (increased gross weight) version of the meg-twin. The fuel capacity was raised from 117335 litres to 171160 litres (the same as the -300), increasing the airliner's range from 8806 to 13230 kilometers.

Furthermore, Boeing has projected two other longer range versions of the aircraft. By stretching the wings to 64,90 m the 777-300X can carry a further 8240 liters of fuel, giving it a range of 12473 kilometers. A designated 777-200X would additionally have additional tanks in the aft fuselage, raising the total fuel capacity to 196600 litres and giving the -200X a range of 16158 kilometres.

For these two versions, Boeing is also considering the installation of a third turbine in the tailcone of the fuselage. The so called auxiliary power and thrust unit with a thrust of 31 to 66,7 kN, would augment the two main engines during take-off and serve as a normal APU during flight. Tail-mounted actuated inlets would open and close like a hinged door and be closed flush with the skin during cruise flight.

From page 42 of FLUG REVUE 9/98