Growing quickly on Air New Zealand’s maintenance base at Auckland Airport is one of the biggest single-span timber arch hangars in the world.
Standing about 10 storeys tall, nearly as wide as the length of a rugby field, Hangar 4 is long enough to fit a Boeing 777 and close the doors behind it.
The project is now about 80% finished and a prominent landmark at the airport after months of lower-profile hard graft on the 10,000sq m building’s enormous concrete slab, which is honey-combed with pipes and tunnels for power, electronics, and drainage.
About 1200 cubic metres of wood will be used in the building, a quantity estimated by contractor NZ Strong to be the equivalent of about 3.5 hours’ growth by all the trees in New Zealand’s sustainably grown plantation forests.
Arches have been traced back to the second millennium BC in Mesopotamia but Air NZ has modern demands for arch structure, largely using industrial scale and incredibly strong plywood.
It needs a cavernous space with no pillars or columns to get in the way of parking planes in its current fleet and new-technology aircraft that haven’t been flown commercially yet and will join the fleet in decades to come.
Using that small mountain of plantation pine grown near Nelson and from Wodonga on the border of New South Wales and Victoria, laminated veneer lumber (LVL) and cross-laminated timber (CLT) form the arches that will provide space for engineers to work on a widebody plane such as a 777 or Boeing 787 Dreamliner and two single-aisle A320/21 jets at the same time.
The airline chose wood because of its strength and flexibility, as it can move by up to 300mm in extreme conditions. It is also part of its sustainability push. What is one of the biggest timber structures in the country could be one of its greenest – it is in line for a 6-star rating from the NZ Green Building Council once it’s built.
Delayed because of the pandemic, the Hangar 4 is now back on schedule and due to be opened sometime around August next year.
NZ Strong pre-construction and innovation manager Jimmy Corric says a wooden building the size of Hangar 4 is attracting international interest.
He says its span is believed to be bigger than another wooden hangar built in Tillamook, Oregon. Built in 1942, the Tillamook hangar housed airships used for coastal patrols during World War II.
While the Auckland hangar will use steel in the front arches to make an absolutely rigid frame for the 80m-wide fabric doors that drop from the roof, the 100% wooden ones in the bulk of the building only use steel in their base plates.
Corric has crafted a scale model of a truss which stands in NZ Strong’s onsite headquarters and he uses it to explain the process.
“Timber and geometry do what they do best. It can wobble about in the breeze, it is a seismic structure. You either make these really rigid structures that constrain everything or you have structures that move a little bit that allow things to give,” he says.
The LVL ply is made by Nelson pine, shipped off to HTL in the city where it is glued into five 25m sections per truss, shipped to Auckland and in Xlam in Mangere where the CLT from Australia is joined to the section before it is taken to the hangar site.
Lying on the concrete slab the sections are joined – hundreds of 250mm long screws are used and driven in by grunty battery tools. The finished trusses are erected using the country’s biggest crawler crane, usually used to put up wind farms. The 38-tonne trusses are stood up to about 85 degrees by the crane and then manually winched to upright by workers on two towers standing next to them.
Next will come the roof, which is made out of ETFE (Ethylene Tetrafluoroethylene) cushions filled with air, providing insulation and resistance to wind. The ETFE cladding system is secured using aluminium extrusions and inflated at low pressure to maintain its structural integrity. It is designed to have high corrosion resistance, important given the area’s proximity to the sea.
It is also very strong over a wide temperature range. The material is used on Forsyth Barr Stadium in Dunedin and other stadiums around the world. The hangar will have more natural light that will cut energy bills, will be warmer in winter and ventilation systems mean it will be cooler in summer.
The new complex allows the airline to bring its firefighting systems and deluge tanks up to strict new environmental standards.
Air NZ’s general manager aircraft maintenance and delivery, Brendon McWilliam, said the older hangars dating back to the 1960s weren’t big enough. He wouldn’t disclose the cost of building Hangar 4 (”eye-watering” is as close as he goes) but he says it would future-proof the airline’s maintenance operation and help anchor it in this country.
“It’s really a great hanger that allows us to be future-focused for our maintenance staff with doors that shut, protecting in all weathers. It’s sustainable and it’s really built around the future of where we want our maintenance to go,” he says.
“The question we’d ask ourselves is, ‘What does maintenance look like in 50 or 60 years?’ We’re in the cycle now where things are evolving so fast. We had to really think and focus around what’s underground – are we going to be running hydrogen are we having electric aircraft?”
McWilliam said using wood fits with the airline’s sustainability goals and lots of clear space.
“We don’t have posts, pillars that we have to work around – it gives us a nice blank canvas.”
The improved workspace would make aircraft checks more efficient. While maintenance regimes tend to be less about stripping aircraft right back as in heavy checks, inspections are more frequent.
The new Hangar 4 will be about 1.5 times as big as the neighbouring Hangar 3, which was built to allow work on Boeing 747 Jumbo jets the airline had delivered into its fleet from the early 1980s.
He said workshops would be built between Hangar 4 and the 1980′s-era Hangar 3 to improve efficiency.
“We really think about time in motion, minimising waste and lean principles.”
Up to 150 workers are on-site.
Grant Bradley has been working at the Herald since 1993. He is the Business Herald’s deputy editor and covers aviation and tourism.
The airline sold its last slots at Heathrow in 2020.