Almost 18 months after cancelling the 747-500X/ 600X programmes, Boeing has finally settled on a firm design configuration for the next version of the 747-400, which could be in service in less than three years.

The long awaited move increases the maximum take-off weight of the -400 to 409,500kg (910,000lb) and range to 14,260km (7,700nm). Perhaps more importantly, the 747-400X - as the proposed variant is described - provides the structural platform for future growth steps, including stretches and wing root insert versions.

Although some details of the "minimum change" growth version have been revealed before as the -400IGW (increased gross weight) version, the -400X is being offered for delivery as early as October 2000. This will entail a firm launch decision no later than December, says 747-400X chief project engineer Gregg Smith. A combi version would be available from June 2001.

Qantas has three 747s on order, which it wants to take as the new -400X. Other likely launch candidates potentially include British Airways, Cathay Pacific, EVA Air, Singapore Airlines and United Airlines, all of which have extra long range payload requirements on routes where they are load restricted. Boeing says that the aircraft, if firmly launched, is likely to be dubbed the 747-400ER.

Programme manager Patricia Rhodes says the aircraft will allow "at least" 6,800kg more payload on existing 747-400 routes, or carriers could use the increased range for new non-stop routes "such as New York to Hong Kong, Los Angeles to Melbourne, or Newark to Taipei". Boeing is pitching the aircraft against the slightly smaller Airbus A340-600 and as an alternative to the long range A340-500 for operators not interested in the proposed 777-200X, such as EVA Air.

Although externally unchanged, the -400X incorporates the strengthened -400F outboard wing and stronger body frames, skin and floor beams. The gear will also be strengthened and have new larger wheels and tyres with the introduction of 777-style, 1.27m-diameter radials for the first time on the 747.

Structural strengthening is also needed to absorb the extra weight of body fuel tanks. These removable tanks, which hold up to 12,040 litres each, will occupy space now used by two potable water tanks, which are being relocated aft to the bulk cargo area.

Boeing believes that most operators will operate with only a single extra fuel tank, although provision has been made for two arranged 0.5m apart at the aft end of the forward cargo hold.

The modifications, which raise total fuel capacity with one tank to 229,600 litres, will increase operating empty weight by 2,300kg, says Smith. The strengthened structure allows further studies of two stretches, says Boeing.

A simple 747-400X stretch, seating up to 70 more passengers, would retain the -400ER wing, but requires 290kN (65,000lb)-thrust engines and offers a 12,950km range. The more complex -400Y is still outlined as a 14,430km range aircraft with an extra 90 seats. Modifications would involve adding 2.3m wing root inserts, along with 303kN thrust engines.

Source: Flight International