Long time coming

The A340-500/600 is the latest Airbus to get the stretch treatment. But the aircraft has more than mere length to recommend it

JULIAN MOXON / PARIS

Airbus is no stranger to stretching or shortening its aircraft to suit market demand. But with the A340-600 it has taken the art to new extremes, producing the world's longest passenger aircraft in the process.

The A340-600, which took to the air for the first time on 23 April, breaks new ground in many ways. It is the first Airbus powered exclusively by Rolls-Royce Trent 500 engines and, with a maximum certifiable capacity of up to 475 passengers, the first to compete directly with the Boeing 747-400.

The aircraft has a new passenger cabin design, which in a three-class arrangement will seat 380, and new underfloor options designed to ease passenger comfort problems on long-range flights - passengers aboard the shorter, longer-range sister model A340-500 will remain in the air for up to 18 hours at a time. Alan Pardoe, director of product marketing for the A330/A340 family, says the aircraft is aimed in particular at operators of older 747-100/200/300s who want a modern replacement. Early -600 buyers fit this description.

Launch customer Virgin Atlantic - an A340-300 operator - has signed for 10 aircraft and eight options partly to replace its five 747-200s, while Lufthansa has 31 A340-300s in service and operates eight Boeing 747-200s. Pardoe adds that while it has around the same seating capacity as the Boeing 777-300ER, the -600's range is 1,110km (600nm) greater.

Orders for the -600 stand at 47 aircraft and 28 options from seven airlines (see table), and the -500 and -600 have amassed 74 orders since programme launch in December 1997. Chief commercial officer John Leahy claims this accounts for 59% of sales in the category, including those for the Boeing 777-200LR and -300ER.

Other programmes have sold faster - the A380 is expected to have booked 100 firm orders by the end of the year, only 12 months after programme launch and five years before it enters service. But Airbus appears unconcerned. "We have a solid order book," says Leahy. "The 340-500/600 will maintain its lead and we expect to see significant interest when the -600 enters service. This aircraft will sell itself once it begins operating."

The -600 represents a major increase in capacity over the A340-300 from which it is derived. It is 10.6m (35ft) longer, providing a 31% increase in payload capacity. The new wing is 20% larger, while range, at up to 13,900km, has gone up by 5%. The result is a claimed 35% improvement in productivity which, according to Leahy, will make for an aircraft with "unsurpassed economics".

Airbus also claims that the four R-R Trent 500 powerplants will cost 13% less to maintain than the two much larger engines powering the Boeing 777, partly because the Trent 500s will operate at 56,000lb-thrust (249kN), 4,000lb less than their maximum certified thrust, stressing the engine less and giving longer component life.

The move to larger engines puts the A340 in a new performance regime compared with its CFM56-powered stablemate, the A340-300. The -300 has done well in the market, its appeal based largely on good economics, low noise levels and reliability.

Performance has not been a main selling point, however. Its Mach 0.82 cruising speed is less than that of many other long-range aircraft, leaving air traffic controllers frustrated by the aircraft's poor station keeping.

The A340-600, according to Pardoe, will fly at a "true Mach 0.83". He also claims the aircraft will climb faster to its maximum operating altitude than the Boeing 777-300ER. "This aircraft will reach flight level 330 (33,000ft/10,000m) in 38 minutes, having flown 330km, while the 777-300ER will take 70 minutes, by which time it will have covered 630km," he promises.

Structural changes

In structural terms the A340-500/600 is much more than a simple stretch of its predecessor, the -300. Besides the longer fuselage and associated modifications, the changes relate principally to greater range (5% for the -600, 20% for the -500), and the need to accommodate heavier engines. The result is a 105t increase in maximum take-off weight and a 64t increase in maximum landing weight.

The A340-600 fuselage has been stretched by 20 frames (see diagram): 10 ahead of the wing, four for the centre section/wing box (as with the -500) and six behind the fuselage. The longer fuselage also means a 38% increase in the area of the new all-composite and all-moving horizontal tailplane, which is made from two carbonfibre reinforced plastic torsion boxes with a titanium centre joint.

The all-composite fin and rudder are taken from the A330-200, but have been reduced by 0.5m in height and 1.5m2 (16ft2) in fin area (a larger tailplane is necessary to control the greater pitching moment caused by power variations in the new engines, while the smaller rudder is possible because of the extra leverage resulting from the longer fuselage).

The design of the forward fuselage is an example of Airbus "mix-and-match" philosophy: sections 12, 13 and 14 are the same as for the -300, section 14 is the same but has the door removed and section 14Bis new and 10 frames longer.

The BAE Systems-designed wing is 20% larger in area and accommodates an extra 53,400l (11,760 gal) of kerosene, a capacity increase of 38% compared to the A340-300 (the -500 contains a further 20,000l in the central fuel tank).

Lifting ability goes up by 40%, while the leading- and trailing-edge structures and moving surfaces have the same basic geometry and layout as that of the -300. Wing growth has been achieved with an insert running the length of the wing, spanning three fuselage frame pitches at the root and tapering out to the tip. The wing itself has been extended by 1.6m. This gives the A340-600 a total wingspan of 63.5m, against 60.3m for the -300.

The (removable) winglets are raked at 31.5í against 29.7í. Around 1t has been saved by removing the wing joint at 62% semi-span, a modification made possible by the availability of aluminium alloys in billets long enough to accommodate the necessary span.

A strengthened four-bogie Messier-Dowty centre landing gear with its own braking system has been introduced, and titanium has been used in both the landing gear and engine mounting pylons to reduce empty weight.

To minimise weight the -600 employs more composite materials than any Airbus aircraft. The Aircell nacelles housing the Trent engines are constructed from pre-impregnated carbon composites, as are the rear pressurisation dome and belly fairings. New aluminium alloys and thermoplastics have been used in panels and hydraulic tubing, giving a further 1t reduction.

Improved comfort

The increasing demand for passenger comfort on the kind of ultra-long ranges the A340 will fly has prompted Airbus to make major changes to the passenger cabin, many of which will feed through to the A380. The main cabin area has been thoroughly restyled and includes extensive use of light emitting diode (LED)lighting, which replaces the old halogen bulbs and provides far greater flexibility in the way illumination is distributed.

The LEDs will have a bulb lifetime "longer than that of the aircraft," says Pardoe. A new touch-screen flight attendant panel has also been developed which allows the display and control of far more data than before, including information on cabin temperature for example. The panel will give flight attendants much more choice in choosing cabin lighting colours and dimming combinations.

Passengers will also benefit from redesigned overhead bins in which the centre support has been made smaller to accommodate three of the roll-on mini-suitcases which have become popular as carry-on luggage.

Design solutions

Airlines will be able to configure the lower deck in a number of ways by using container-sized roll-on/roll-off modules developed by Airbus. Crew rest compartments, extra toilets and lower-deck galleys will be accessible from a rear stair. "We've tried to modularise the design to provide a lot of solutions based around a common modular concept. We've already sold both full and partial bulk crew rest options," says Pardoe.

He admits, however, that it has taken "a lot of clever design" to find the right balance between providing flexibility for passengers as opposed to cargo. "The market says freight is vital. The -600 will have potentially twice the cargo volume of the 747 and some airlines have indicated they intend to use it," Pardoe says.

Developed specifically to power the A340-500/600, the Trent 500 breaks new ground in being the first R-R powerplant to power an Airbus from entry into service.

R-R's relationship with Airbus began in the early 1980s when it joined with Pratt &Whitney and Japanese Aero Engines to develop the International Aero Engines V2500, which became the second powerplant specified for the A320 family.

The Trent family's development began with the 68,000-72,000lb thrust Trent 700, the first engine to enter service powering the A330-200/300. Selection of the 53,000-56,000 thrust Trent 500 was announced at the 1997 Paris air show, the engine having been the subject of an "exemplary" development programme. According to R-R's civil aerospace president, John Cheffins, "all milestones have been achieved on or ahead of schedule".

Now, R-R is preparing for the fastest ever production ramp-up of one of its "big fan" engines, entering what Trent 500 programme director Ian Kinnear calls a period of "intense activity". The rate is planned to grow from 20 engines this year to 150 per year in 2003 in support of Airbus' own rapid delivery programme.

The Trent 500 features the same three-shaft design philosophy used in all of the company's big fan engines, going back to the first RB211 developed for the Lockheed TriStar in 1970. One of the advantages claimed by R-R for three shafts is the ease with which engines can be scaled to suit aircraft power requirements.

In the Trent range, turbines and compressors have been scaled independently to create a family with thrusts ranging from 50,000lb to more than 100,000lb. The Trent 700 high-pressure core has been retrofitted to the existing RB211 to create the RB211-524G/H-T and two new derivatives, the Trent 900 for the Airbus A380 and the Trent 600, aimed at the Boeing 747X, are under development, both featuring swept fans.

While essentially a scaled version of the Trent 800, which powers the Boeing 777, the Trent 500 uses the smaller 2.47mdiameter Trent 700 fan. The derivative approach means that only proven components are used. "It was one of our precepts that there should be no unproven technology in this engine," says Robert Nuttall, Trent 500 head of marketing .

This is intended to help the engine set a zero in-flight-shutdown (IFSD)rate from entry into service (EIS). "We're being much more aggressive on reliability", he adds. "We sat down with Airbus at the beginning of the programme and decided that to target any other IFSD would be unacceptable".

Initial ground testing took the Trent 500 to 68,000lb thrust to establish running limits, but the engine will be certified at 60,000lb, which leaves plenty of temperature margin at the 53,000lb/56,000lb A340-500/600 operational thrusts. The first production engine was delivered to Airbus in March last year and installed on an A340-300 flying testbed, accumulating 80 flight hours and 150h engine running. Even though the A340 is a quad, cycle tests follow extended range twin operations and have been doubled to 2,200 cycles.

Modified controls

Like all modern Airbus aircraft, the A340-600 shares a common cockpit design with other aircraft in the fly-by-wire range, based on sidestick controls which signal the flight surfaces via flight-control computers. The computers confer similar handling characteristics to all Airbus aircraft bringing major cross-crew qualification advantages, one of Airbus' big selling points.

The main instrument panel has six screens: two electronic flight instrument system flat panel displays in front of each pilot, next to which are a pair of navigation displays. In the centre, one above the other, are the engine warning display and systems displays. All displays are interchangeable.

Six conventional electro-mechanical instruments are situated on the centre panel and serve as standby instruments. Multipurpose control and display units are located on the centre control pedestal, combining screens and keypads and providing access to the flight management system and systems maintenance data.

For the first time, the rudder has been included in the fly-by-wire flight control system, leaving only the pitch trim under mechanical control. Airbus' flight dynamics team has also improved the "comfort in turbulence" feature installed on the A340-300 to counter aircraft movement in roughair by integrating it fully with the flight control computer's manoeuvre functions.

The -600 is fitted with new sensors in the fuselage to provide feedback to the computer, which then signals the rudder and elevator to counter movement of the ultra-long fuselage. "The frequency we want to control is 2-3Hz," says Vincent Rivron of Airbus flight dynamics team. "The challenge with the -600 was to control both the 2Hz fuselage bending frequency while providing full handling capability". Computer architecture has, he adds, been "optimised" to reduce computer-computer and computer-sensor time delays.

Throughout the A340-500/600 design process emphasis has been placed on the long-range aspects of their role. This centres naturally on the need for extreme systems reliability and redundancy, with the aim of eliminating most of the causes of en-route diversions that on some of the routes being considered, such as those over the north and south poles, require the use of alternate airports located in extreme and therefore undesirable environments.

It addresses systems such as pressurisation and air bleeds, fire protection, reliable long-range communications, hydraulics, anti-skid brakes, oxygen provision, also covering items such as crew fatigue and the associated provision of crew rest areas.

Airframe reliability

Airbus has also concentrated as never before on achieving early reliability both in the airframe and the passenger cabin. At entry into service (EIS) with Virgin Atlantic in June next year the intention is that the A340-600 will already be a mature aircraft in terms of the exceptional amount of testing of the airframe, engines and systems carried out during the programme.

The target for EIS despatch reliability is 98.5%, increasing to 99% after a year in operation. This follows four years of development that Airbus says contained the longest test and validation programme it has ever carried out, which is now peaking as the -600 is put through its flight test programme.

The A340-500/600 programme is seen by Airbus as a stepping stone to the A380 as far as cabin comfort, systems reliability and advanced design are concerned. The pair cost $2.9 billion to develop, against $3.5 billion (today's dollars) for the initial versions of the A330/A340, reflecting both the greater standardisation of the new aircraft as well as improvements in design efficiency resulting from the introduction throughout the Airbus partners of the CADDS-5 three-dimensional design system.

The introduction of CADDS-5 also caused problems for one partner, BAE Systems, which suffered delays to wing production because some of its suppliers were not equipped with it. This meant a three-month delay to both programmes and to deliveries.

Virgin Atlantic will therefore receive its first -600 in June next year instead of March, while the first -500 will arrive at Air Canada in November 2003 instead of November next year. In 2002, Airbus will deliver 16 instead of 21 aircraft, the last three of which will be delivered on time. The remaining five aircraft, all -500s, will be delivered in early 2003. "We will recover back to the contractual dates by early 2003," says Pardoe.

Early maturity

"Achieving maturity at the earliest possible moment is the most important aspect of the programme," says Daniel Therial, senior vice-president long-range programmes. Three main areas have been covered: deliverables (the aircraft itself, accompanying documentation, training, tools etc) user satisfaction (maintenance, cockpit, cabin crews and passengers) and significant reduction in post EIS problems.

Twelve "key maturity subjects" were identified: cabin, cargo loading, electrical generation, flight controls, hydraulic system, structure, built-in test and on-board maintenance, landing gear, fuel system, bleed air, powerplant and lower-deck facilities.

Each is under constant review. "We've made more than 500 significant improvements as a result," Therial says. Combined endurance and environment testing has been carried out at equipment level while entire systems are tested on rigs, including a new full-scale water/waste and new landing gear rig. A new cabin avionics rig is being used to test items such as the in-flight entertainment and communications systems. A dedicated -500/-600 "iron bird" rig has also been established to test hydraulics and other systems running throughout the aircraft.

Airbus has held maturity vendor conferences with suppliers to "share challenges and identify responses as early as possible," says Therial. Specific exercises have also been defined to ensure cabin maturity at EIS, which will include early flights with passengers six months before EIS to identify any cabin comfort modifications. Long-range route-proving flights will also be carried out with full passenger loads.

Preparation for the first flight included application of 60% static limit loads on the second of the three dedicated -600 flight test aircraft (MSN360/MSN371/MSN376) before the maiden flight.

The first aircraft, MSN360, launched the flight test programme on 23 April with a successful 5h 22min maiden flight from Toulouse. It will remain in Airbus colours and be used for demonstrations and development after flight testing, as well as for general development and certification. MSN371 will fly in mid-June and carry out general development and powerplant-related certification while the third, MSN376, will carry out cabin systems, cold weather and long-haul trials, planned for November, leading to passenger proving flights in March next year. Airbus expects testing to last 1,600h but has provided a further 300h contingency time.

The aim is to achieve type certification in April 2002.

Production

Final assembly of both of the new A340 versions will take place in Airbus' Clement Ader factory in Toulouse integrated with the A330/340 models. The addition of the new types will take the monthly production rate to eight and possibly nine aircraft. By the first flight of the prototype, 19 A340-500/600s had been launched into production with rates building from 16 aircraft next year to 35 in 2003 and 39 in 2004.

Source: Flight International