Boeing engineers have released for production 90% of the design drawings needed to build the new 757-300 and the company has started major assembly of the wing spars for the first aircraft.
According to Boeing spokeswoman Cheryl Addams, the leading edge - made by Boeing Vertol in Philadelphia - will be attached to the four-spar wing structure next week and the company has started drilling door parts for the first test 757-300.
Addams adds that Northrop has begun preliminary assembly of the first aircraft's tail section, officially known as Section 48. Northrop is making the fin, horizontal stabilisers and tail cone for the 757-300.
Boeing vice president of 737/757 derivative programmes, Jack Gucker, says the 90% completion of design drawings is a milestone in the development of the 757-300.
"Reaching this milestone means that we are nearing completion of the development phase of this airplane programme and moving ahead to production," he says. "Our programme is right on track and we're proceeding toward an on-time delivery of the first 757-300 in January 1999."
The first aircraft is due to enter final assembly in March, with roll-out scheduled for 31 May 1998. It will be delivered after certification to Lufthansa subsidiary Condor Flug, the launch customer for the type. The release of the remaining 10% of the engineering drawings necessary will be gradual, says Addams, and might continue up until May depending on whether Condor Flug wants to make any last-minute changes.
Boeing says that more than half of the components of the 757-300 have been designed digitally using computer-aided design software. This is a far cry from the designing of the original 757-200 in 1981, when most of the engineering drawings were hand-drafted.
The much greater use of digital design in the 757-300 - despite its substantial commonality with the existing 757-200 - has come about for three reasons, says the manufacturer.
First is that all the new portions of the aircraft have been designed digitally. These include the interior of the passenger cabin, the 12 extra-long skin panels needed to stretch the fuselage by 7.1m (23ft 4in) over that of the 757-200 and a more powerful air conditioning system, required for the extra 40 passengers the aircraft will carry.
Second is that about 80% of the 757-300's wing design is digital, even though it is essentially the same as that of the 757-200.
This is because the drawings had to be digitised to feed information into the new computerised spar-assembly system - known as automated spar assembly tool, or ASAT - that Boeing is using for the first time to manufacture 757 wings. The company originally developed ASAT for production of the next-generation 737 models.
Third is that drawings for other parts of the 757-300 that are identical to the 757-200 have also become digitised as the company has made changes to the 757-200 over the years.
Addams says the use of ASAT and the company's decision to design stretched fuselage panels rather than use fuselage plugs to increase the length of the 757-300 over the -200 are the two really new features of 757-300 production.
The 757-300 will carry 20% more passengers and nearly 50% more cargo than its smaller sister. Boeing says the 757-300's higher seat capacity will give it about 10% lower seat-mile operating costs than the 757-200.