Boeing is starting work on the 1,000th 777, a Boeing 777-300ER destined for delivery to Dubai-based Emirates Airline in March 2012.

Emirates is the largest 777 customer with 95 777s currently in its fleet and the 1,000th aircraft will be the Middle East carrier’s 102nd.

Some 970 Boeing 777s have been delivered, and with the upcoming milestone next year, the 777 will become the seventh heritage Boeing jetliner to reach 1,000 deliveries, joining the 707, 727, 737, 747, 757 and 767. The McDonnell Douglas MD-80 also exceeded 1,000 deliveries. Firm orders for the 777 now stand at 1,295.

The start of assembly of the milestone aircraft comes 16.5 years after the 777 entered commercial service. The event also illustrates the quickening pace of twin-aisle production and, more strikingly, how the assembly rate for the mid-size widebody sector is on its way to doubling since the advent of the 767.

Boeing officially starts assembly of a new conventional metallic aircraft when it loads the first wing spar into the production tool. Approximately 18 years and 10 months have elapsed between the loading of the spars for WA001, the first 777-200 in January 1993, and start of work on the spars for the 1,000th aircraft.

The 767, by comparison, took just over 31 years from the loading of the first wing spar on the initial -200 to the same milestone on the 1,000th aircraft in September 2010. Assuming the 787 production rate climbs to the planned 10 per month by the end of 2013 and the program stays on a smoother course during the development of the 787-9 stretch, the new twinjet should reach the 1,000 delivery mark by 2021. Although this event will occur at least two years later than Boeing originally planned, the milestone still will pass after a period of just under 15 years, or half the time taken for the 767 to hit the same landmark.

The 747, by comparison, took just over 25 years from the laying of the first wing spar to the start of assembly of the 1,000th aircraft, 747-400 delivered to Singapore Airlines in September 1993. A further 421 have been delivered over the intervening 18 years.