Photo: 123RF
Bird strike is being blamed after flames were seen coming out the back of a Boeing 737 that made an emergency landing in Invercargill this week.
Virgin Australia flight VA148 departed Queenstown Airport just before 6pm, bound for Melbourne, before turning around and landing safely in Invercargill an hour later.
The plane "experienced an issue just after take-off and has been diverted to Invercargill Airport", Queenstown Airport said in a statement. It's believed the cause was bird strike.
Bird strike has affected planes since they were first invented. And despite technological advances helping to predict bird movements, it's likely to be an issue for a long time to come.
What happened on Monday?
Videos shared on social media appeared to show flames coming from the plane as it flew over the Shotover Delta. (The New Zealand Air Line Pilots' Association said while flames appeared to arise from the rear of one of the engines, the aircraft or engine "was not actually on fire".)
One Queenstown man told RNZ he heard what he thought was a car back-firing before seeing the plane.
Passenger Michael Hayward said he heard a bang and noticed flames coming from the engine compartment shortly after the plane became airborne.
"I was sitting just behind the wing ... you could almost feel the heat of the flames through the cabin," he said. "There was definitely some anxiety."
Virgin Australia chief operations officer Stuart Aggs in a statement said the aircraft was met by emergency services at Invercargill Airport. No one was injured.
When asked whether bird strike had been confirmed as the cause of the incident, an airline spokesperson on Wednesday said no further updates were available.
Queenstown Airport said no birds were detected on the airfield during a routine inspection just before the flight took off. But after the incident, a member of the Airport Emergency Service team found the remains of a mallard duck.
At this stage, the Civil Aviation Authority isn't investigating. And the Australia Transport Safety Bureau is gathering further information before deciding whether it will investigate.
What's bird strike?
Wildlife strike is the umbrella term, because while most cases involve birds, there have been cases of other animals, and even people, getting sucked into the running turbine engine of a plane.
The first reported bird strike is said to have occurred in 1905, when the Wright Flyer flown by Orville Wright struck a bird over an Ohio cornfield.
The most well-known case of bird strike is that of US Airways Flight 1549 in 2009.
Shortly after pilot Chesley "Sully" Sullenberger took off from New York's LaGuardia Airport, two large geese flew into each of the plane's twin engines. Both engines stopped working, and the pilot had to choose between trying to reach an airport runway or attempting a water landing.
Sullenberger aimed for the Hudson River, and everyone aboard survived.
This was a very rare and unfortunate case of both engines being out of action.
It's unusual for planes to lose even one engine while flying, and modern, twin-engine aircraft are designed to be able to rely on just one. They won't have the maximum thrust power for take-off, but they can continue to fly and land, Professor Doug Drury, head of aviation at CQUniversity Australia, says.
What happens?
Anything ingested by a turbine engine "becomes shrapnel", Drury says. The damage caused will depend on the size and number of the birds involved.
There will be a loud noise and possibly flames, he says. The pilot will shut down the engine and divert to another landing area.
In theory, it could continue flying to its destination. "We [pilots] don't want to take risks if we don't have to," Drury says.
Airlines can also get fined for putting passengers in jeopardy.
"We train extensively for single-engine operation. The Virgin crew did exactly what they were trained to do."
It's important to keep in mind, despite these types of events, that "flying is still the safest mode of transport", he says.
How common is it?
In New Zealand, the bird strike rate at airports is about four in 10,000 aircraft movements, according to the New Zealand Aviation Wildlife Hazard Group (NZAWHG).
About 90 percent of cases occur at low altitudes at airports, during take-off or landing, according to the group.
Worldwide, it causes more than $1.2 billion in aircraft damage annually.
Queenstown Airport says bird strikes are a known risk to aviation around the world. But the Civil Aviation Authority has recorded the incident rate for bird strikes at the airport as "low".
"The primary species of concern at Queenstown are oyster catchers and plovers, along with smaller birds such as finches, starlings, and sparrows."
While the "vast majority" of strikes are by birds, there have been cases in New Zealand of planes colliding with rabbits, according to the NZAWHG.