QUALITY control is a big responsibility for anyone, but the responsibilities do not come much bigger than for Boeing 747 jumbo jets. Peter Gardner and Leonard Tranter are Cathay Pacific's men based in Seattle, where their job is to make sure the airline's new US$140 million 747-400 aircraft roll down the giant Boeing production line at Everett Field as smoothly as possible. When Mr Tranter joined Cathay Pacific 20 years ago, it was very much a regional airline. By the time Mr Gardner stepped aboard in 1982 it had joined the wide-bodied market but, with 14 aircraft, was only just beginning to spread its wings. Today Mr Gardner and Mr Tranter, Cathay's vice-president and assistant vice-president, technical (US), respectively, are the permanent links between the airline and Boeing. And that also means keeping an eye on the development of the new member of the Boeing family, the 777, which is scheduled to enter service in May 1995. They are also the links between the two parties in a project that could change the whole face of aviation in the next century - the super jumbo or extra-large aircraft, as the industry chooses to call the concept. Once Boeing wheels out its brand-new aircraft, Mr Gardner and Mr Tranter are on hand to arrange test flights and checks to make sure the machine is in tip-top shape for Cathay to take ownership. There are three more 747-400s on order, to add to the fleet of 15 it has already, and two 747-400 freighters. There are also options on the nine 747-400s and two more freighters. The current Boeing 747 family, however, is tried and tested. The buzz around the Everett facility at the moment is production of the ''new baby'', the Boeing 777, for which Cathay has 11 orders, and beyond that the super jumbo. The airline has said it might well be in the market for the plane, which could carry between 640 and 1,000 passengers. Cathay is one of nine airlines with offices at Boeing. Its engineering and design staff have continuing consultations with Boeing about new developments. The airline says the aircraft manufacturer is one of its closest allies and has made a significant contribution over the years to aircraft design. For aviation industry veterans such as Mr Gardner and Mr Tranter, it is all very different from their humble beginnings in the industry. Mr Gardner started his career overhauling piston engines in the mid-60s. In 1969 he joined the now-defunct Laker Airways, where he was in charge of fleet maintenance. During his 12 years with the airline that revolutionised air travel with its cheap tickets, Mr Gardner gained vital management experience. He even flirted with the idea of starting his own airline after Sir Freddie Laker was forced out of the skies. But in 1982 he joined Cathay. ''It only had 14 aircraft but I thought the company showed promise,'' said Mr Gardner, who was in charge of quality control and air worthiness. He has witnessed outstanding growth within the airline. This has particularly been the case over the past 21/2 years since Mr Gardner has been based in Seattle. In that time he has overseen the delivery of 10 Cathay 747-400s. It is perhaps a tribute to Mr Gardner that when director of engineering Stewart John, who is retiring in December, was asked what had given him greatest pride during his career at Cathay, he said: ''A safety record and reputation for engineering excellence that is the envy of the industry.''