Airbus believes it is close to correcting a fuel management software glitch that contributed to a Virgin Atlantic Airways A340-600 diversion earlier this year. In related work, Airbus also has begun a fleet-wide retrofit program that should eliminate false fuel system fault messages.

The moves come as Airbus addresses reliability issues attributed to its simultaneous introduction of a new fuel system and a new supplier on A340-500/600s that began to enter service in late 2002. Airbus had changed its equipment source following unreliability in the incumbent vendor’s A340-300 system. After the Virgin diversion, Airbus has suggested that operators frequently confirm the appropriate transfer of fuel between tanks.

By the beginning of April, almost 60 of the new aircraft served with 10 operators; all but 16 were the larger A340-600s. Intended as long-range derivatives of the established A340, the Rolls-Royce Trent 500-powered A340-500 and -600 sport many differences that have led operators almost to regard them as new types.

Maximum takeoff weight for the A340-500/600 family represents almost a 100-ton increase over that of the A340-300. In comparison with the earlier variant, new parts make up roughly 65 percent of the latest models. Following industry consultation, the manufacturer made more changes than planned, some being late in the development program, effectively reducing systems maturity at service entry.

Originally launched eight years ago, the A340-500 and -600 compete against the Boeing 777 and the larger 747-400 by offering heavier loads or longer range. The Airbus models carry 313 passengers over 9,850 miles and 380 passengers over 8,675 miles, respectively. By comparison, the long-range 777s transport 301 passengers over 9,400 miles or 365 passengers over 7,100 miles, while the long-range 747-400ER flies 416 passengers over 8,670 miles.

Early problems notwithstanding, A340-600 launch customer Virgin Atlantic has increased its orders for the aircraft, despite strong competition from the Boeing 777-300ER. Expecting extensive industry consultation to ease service entry, the airline expressed surprise with the relatively poor despatch reliability early on. The selection of suppliers ahead of the setting of reliability standards, which effectively removed competitive incentives, appeared a significant factor.

Virgin Atlantic has configured the larger A340 in a three-class layout with 311 seats, plus a massage area. London-Hong Kong services carry 305 passengers, allowing capacity for some 20 tons of revenue-earning underfloor freight. In contrast, German carrier Lufthansa has configured its A340-600s for 347 travellers in business- and economy-class cabins only.

After rejecting the 777, Spain’s Iberia Airlines has opted for A340-600s with a 352-seat, three-class layout. On its smaller A340-500s, Singapore Airlines (SIA) has employed a generous two-cabin arrangement with just 181 seats.

Virgin Atlantic launched A340-600 services on the North Atlantic to build experience quickly over relatively short routes, while the longer-legged A340-500 began service with Emirates Airline 18 months ago with 14 hour flights between Dubai and Sydney. In June 2004, Singapore Airlines began using the -500 for nonstop operations to New York, establishing the world’s longest scheduled service at some 18 hours duration.

At first Virgin trained A340-600 pilots for mixed-fleet flying (MFF) with a minimum of six months’ A340-300 experience. Subsequently it assigned some pilots  directly to the larger aircraft. Most of their training was on the -300 and augmented by four A340-600 sectors flown before MFF qualification.

SIA has elected not to introduce an A340-600 simulator, preferring to outsource such training capacity. Quick training proved an early challenge, since two crew fly each long-range service and trainers needed to understand the physical and medical implications of such operations.

The airline has assigned two aircraft each to its Los Angeles and New York operations, with the fifth of its five A340-500s often serving Jakarta. The latter route allows pilots to record additional service experience on shorter-range sectors. The U.S. flights see pilots logging five roundtrips every 56 days, equating to between 75 hours and 80 hours per 28-day period.

Singapore aviation regulators have concluded that on the very-long U.S. services crews should have two rest periods of at least four hours, with each flight preceded by four off-duty nights. They specify two-night layovers on both U.S. east and west coast flights, but usually pilots stop over for three nights.

Airbus appears to have learned from the early A340-500/600 service experience, judging by the testimony of many operators to the strong support from the manufacturer and other suppliers, including engine-maker Rolls-Royce. Carriers generally aim for a dispatch reliability of 98.5 percent, supported by Airbus, which has been generating service bulletins and modifications to address technical issues.

A major change for operators also flying the A340-200/300 is a switch from CFM56 propulsion to 53,000- to 56,000-pound-thrust Trent 500 power. The move has transformed performance, compared with the earlier variants, which have earned a reputation for shallow climb profiles.

Rolls-Royce reports the best service-entry reliability of any Trent, with the long-haul flights generating flight time very quickly (although cycles are naturally building much more slowly). The UK group says that engine removal and in-flight shutdown rates have proven lower than those for the Trent 700 and 800 after equivalent service experience.