Cathay Pacific is bringing some of its planes out of an Alice Springs "boneyard" as it rebuilds its network.
The airline parked up to 70 per cent of its fleet of nearly 180 aircraft at the height of the pandemic.
Near the Northern Territory town it parked 70 Boeing and Airbus wide-body planes and has other aircraft parked at its Hong Kong home base and at Ciudad Real in Spain.
It explains how it managed this unprecedented operation involving multiple locations around the world: "With lots of planning, co-ordination, and even more heart," the airline says.
Cathay Pacific is one of the hardest hit by the pandemic as it does not have a domestic network and continues to be affected by China's strict Covid-zero approach.
However, it is slowly rebuilding in New Zealand as restrictions in Hong Kong are gradually relaxed, stepping up from one flight a week to two flights in October.
Alice Springs has proved an ideal location for storing planes.
"The biggest enemy of a parked aircraft is corrosion from sitting on the ground for long periods in humid conditions – especially when located in a coastal environment where that humidity has a salt content," says Benjamin Connell, regional engineering manager southwest Pacific.
"That's why we chose Alice Springs. It's in the desert where it's inland, very dry, with a low humidity of around 20 per cent, and no extreme weather events like tropical cyclones."
Other carriers including Singapore Airlines, Fiji Air and Cebu Pacific stored planes in Alice Springs.
Aircraft boneyards are traditionally where old aircraft are stored before being dismantled and used for parts, but during the pandemic hundreds of near-new planes were temporarily parked up. In remote Alice Springs, population just over 25,000, the site became a local landmark.
While the desert was good for aircraft storage, it presented unique challenges for teams on the ground.
"One of the issues with being based in Alice Springs is that by about 8am the surfaces of the aircraft are too hot to touch - we could literally fry an egg on them – so the team have to plan their maintenance schedules quite differently," Connell says.
The desert terrain was also a challenge. Unlike the firm foundations of an aircraft hangar and the surrounding aircraft stands and taxiways, at Alice Springs aircraft are parked on compacted strips of soil and concrete that are mixed to form a hard surface.
Performing maintenance around the limited size of these parking strips can be challenging, and moving aircraft also requires complex and special towing procedures.
Even the local wildlife has been a factor. "I was talking to an engineer one day when a giant goanna [lizard] walked out of the grass, straight past us and between the landing gear."
The unprecedented scale of the aircraft storage operation was a huge challenge in itself.
"Parking aircraft at Alice Springs is not something many of the team have done before, and certainly not on this scale, so in many ways it was exploring uncharted territory," says Pearl Sau, line maintenance operations manager, in a post on the airline's website.
As Alice Springs isn't a commercial airport, the airline had to liaise with numerous authorities for special authorisation and flight permissions to fly the aircraft to the site.
"Another huge challenge was shipping the necessary spare parts, tools and equipment required in Alice Springs," says Sau.
"With all the travel restrictions in place, and the very low frequency of flights between Hong Kong and Australia, it was incredibly difficult for us to arrange the shipping logistics."
The maintenance required for a parked aircraft is just as much as for an aircraft that is flying, she says.
"Safety and maintaining compliance with manufacturer and regulatory airworthiness requirements is our number one priority, whether the aircraft is flying or not – and we have to ensure the aircraft are maintained in a condition where they are able to be reactivated to re-enter operational service when required."
The first phase of parking an aircraft is called the induction, which takes around 14 days per plane. This involves covering windows, external surfaces, instruments, sensors and any openings.
Workers had to secure the engines, replace the engine oil with inhibiting fluid to prevent corrosion and introduce additives to fuel tanks to prevent microbial growth.
Then came set periodic checks, with maintenance checks to carry out at regular intervals after seven days, 14 days, 30 days - up to a one-year check.
The final phase is reactivation, which takes about four to six months of planning, plus four weeks of solid work by the engineers.
But again, the process isn't straightforward, says Connell.
"Every reactivation is different and presents different challenges."
Engineers had to reverse everything they did during the induction process: removing the inhibiting oils, adding fresh oil, removing protective covers and addressing any maintenance issues.
The engineers work through a detailed manual, which also covers the engines.
"The Aircraft Maintenance Manual provided by the manufacturer provides a comprehensive list of tasks that need to be performed at a specific interval when an aircraft is in a parked condition."
Then it's on to testing of engines, systems and components to ensure the aircraft are fully airworthy for the flight out of Alice Springs.
Connell says the aircraft the engineers had worked on were in good shape and free of dust or wildlife because they were so tightly wrapped up and maintained.
They had also started first time.
Because of travel restrictions and crew quarantines - particularly strict in Hong Kong - even getting the flight crew to Alice Springs was complex. Often, the outbound flight crew had to be dropped off by diverting a regular cargo flight.
"It's definitely a challenge, but there's a huge sense of satisfaction when an aircraft departs Alice Springs and you receive feedback from the crew that the aircraft flew beautifully and had no issues," says Connell, who has more than 30 years' experience in aviation engineering.
Aircraft tails glimmering in the desert provided an awe-inspiring sight, he says.
"It's very difficult to convey just how excited we all are at Cathay Pacific. As engineers we've really bonded to these aircraft, we know them inside out. We've lovingly cared for them while they have been in storage, and now we can finally see them back in the air and returning to the skies," Connell tells the Herald.
"It really does mean so much to us, personally and professionally. There is a huge sense of satisfaction every time we send one back to Hong Kong."
Thankfully, the pandemic's peak appears to have passed, and now teams are busy with reactivating rather than inducting aircraft.
Cathay Pacific traffic figures for June reflected the positive impact of further adjustments to the Hong Kong Government's easing of travel restrictions and quarantine requirements.
The airline carried a total of 150,077 passengers, an increase of 269.2 per cent compared to June 2021, but a 95.2 per cent decrease compared to the pre-pandemic level in June 2019.
The risk of not getting reactivation right was identified early in the pandemic by the European Union Aviation Safety Agency (EASA), which as early as 2020 reported an "alarming trend" in the number of reports of unreliable airspeed and altitude readings during the first flight after a plane leaves storage.
In some cases, take-offs had to be abandoned or the aircraft had to return to base, Reuters reported.
In most cases the problem was traced back to undetected insect nests inside the aircraft's pitot tubes, the pressure-sensitive sensors that feed key data to an avionics computer. Insects need to be flushed out of data lines from pitot tubes with nitrogen to ensure they are clear.
Bigger creatures were also a threat.
In mid-2021 the Herald reported Qantas engineers being on alert for snakes around planes stored at Victorville, on the edge of the Mojave Desert in California.
"The area is well known for its feisty rattlers who love to curl up around the warm rubber tyres and in the aircraft wheels and brakes. Every aircraft has its own designated 'wheel whacker' (a repurposed broom handle) as part of the engineering kit," the airline said.
Before unwrapping the wheels and starting any ground inspections of the landing gear in particular, engineers walked around the aircraft stomping their feet and tapping the wheels with the wheel whacker to wake up and scare off the snakes.
It has since brought back more of its A380s as it has expanded its network.
Air New Zealand has written off its older 777-200s but has this year progressively been bringing back its 777-300s, with Planespotters.net listing four parked at Victorville in southern California and one at Auckland Airport. It brought back the first of its Auckland-based planes in February after 600 days of sitting idle.
Chief executive Clive Mackenzie said the results gave the company even greater confidence.