The Hutt's J&D McLennan Engineering are the only air bridge manufacturers in Australasia.

Knowing that generations of Kiwi travellers have traipsed all over the work of his family's business gives James McLennan great satisfaction.

McLennan is the workshop manager for J & D McLennan Engineers, a Lower Hutt company that specialises in making air bridges – the raised tunnels that protect passengers and crew from the elements as they board aircraft from the terminal gate.

In an age where more people are flying than ever, the air bridge might be an easy piece of infrastructure to overlook at a sprawling airport but McLennan still likes seeing his creations in use.

MAARTEN HOLL/STUFF James McLennan, workshop manager at J & D McLennan Engineers, is the third generation of his family to build air bridges.

"Whenever you see something that you've pushed from the planning stages to completion, it feels good. Especially when you've done something out of the ordinary, it gives you a sense of pride."

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The company was founded in the 1940s as a general engineering firm by his grandfather and great uncle and has been producing air bridges since 1974. McLennan is part of a third generation of engineers in his family to have worked at the company.

MAARTEN HOLL/STUFF James McLennan inside a nearly finished air bridge.

While they still take on general engineering projects, air bridges and other airport equipment makes up most of their work. J & D McLennan has rolled nearly 300 of the structures out the workshop doors over the years.

Having produced all the air bridges in use in New Zealand, McLennan would be able to go to any major airport in the country and point out his company's work.

The company is the only one in Australasia to make passenger boarding bridges and also has clients dotted all over Australia and the Pacific.

SUPPLIED An air bridge makes a night-time departure from the J & D McLennan workshop.

While it could not compete with its competitors in China, India and Spain on price, McLennan believes their advantage is in service and workmanship.

"We'd expect our bridges to have a 20-year-plus service life."

In 2005, the company scored a coup when its bridges became the first in the world to link simultaneously with both decks of the then new Airbus A380 in Melbourne.

MAARTEN HOLL/STUFF Air bridges are fabricated over two to three weeks and final assembly takes place at the airport after being delivered.

The bridges are made under licence from American company Jetway and the designs are made to imperial measurements.

Sourcing the components, right down to the nuts and bolts, in imperial units is no simple task in a country that had used the metric system for 45 years, McLennan says.

It took two to three months to get the materials and components together. About three weeks are spent fabricating each bridge, which typically weighs more than 30 tonnes and can telescopically extend from 58 feet to 110ft.

The units were moved out of the workshop in parts by truck and were assembled at the point of delivery.

The size of the bridges made them difficult to shift. Moving them usually took place at night to minimise the impact on traffic, and their routes had to be planned to ensure there were no low bridges or tight turns.

"They're too long, too wide, too high and too heavy, all that good stuff," says McLennan.

For McLennan, continuing the work at the family company is a special feeling. His father, uncle and brother have also been involved with the business over the years.

"That means a lot; to carry on doing the same thing. Especially in Wellington where manufacturing is not so flash, we're still carrying on [and] keeping it going."