GUY NORRIS AND PAUL LEWIS / SEATTLE
Manufacturer says the "get well" programme will include design modifications to the wing structure
Airbus says weight reductions and engine improvements will be gradually phased into initial production A340-500/600 aircraft. This is to ensure that the first aircraft for Singapore Airlines can meet critical transpacific payload-range targets on the key Los Angeles-Singapore route by 2003.
The bulk of the changes are in the BAE Systems-designed and built wing which has contributed most to the weight problem, thought to be in the region of 2,200kg (850kg).
Although suspected as far back as 1999, the exact scale of the weight issue is now believed to have been verified by recent flight tests of the initial A340-600 test aircraft. Despite better than expected aerodynamic performance overall, there is the potential for payload/ range shortfall as a result of increased weight and the impact on predicted fuel burn performance from the aircraft's 53,000-55,000lb-thrust (236-245kN) Rolls-Royce Trent 500 engines.
Airbus says the resulting "get well" programme combines BAE design modifications to the wing structure with a R-R planned engine enhanced performance (EP) package. The first of these is in initial validation tests and is believed to include scheduling changes to the full authority digital engine control, reduced clearances in the intermediate pressure compressor and alterations to increase the turbine exit temperature. R-R believes the additional margin built into the Trent 500 design by certificating at 60,000lb-thrust will reduce the impact of the operating temperature increase.
Weight reductions are expected to be achieved by reducing material used in various stringers and ribs in the wing, as well as by taking out additional mass from some of the larger forgings within the structure. This is made possible because of the extra long billets of aluminium being used for the first time on the A340 wing by BAE. The larger pieces allowed the manufacturer to remove a large wing joint at the 62% semispan, and have already saved around 1,000kg in structural weight. BAE plans to gradually phase in the structural changes until reaching the optimum configuration on aircraft No 24 (first A340-500) for SIA which is due for delivery in the second quarter of 2003.
It is unclear if the Trent 500 EP will be ready in time for the first scheduled SIA delivery, but the package will be retrofitable. The changes are critical to meeting the airline's requirement to operate year-round on the 16,260km (8,790nm) route between Los Angeles and Singapore while carrying 200 passengers.
The ability to perform the mission was vital to winning the key victory over the Boeing 777-200LR, which the US manufacturer is still seeking to overturn.
The development is the latest in a series of weight-related issues to impact the A340-500/600 programme. These date back to at least 1999 when Airbus confirmed it was asking member partners to study a 7,000kg take-off weight increase. This, it insisted, was aimed at increasing margin for future growth rather than to compensate for excessive weight. In February last year Airbus conceded the aircraft were slightly overweight, but believed the positive windtunnel results showed that both models would still exceed nominal range targets.
Source: Flight International
