Bird strikes explained: Queenstown Airport says no sign of birds before Virgin Australia plane was hit

A Virgin Australia Boeing 737 diverted to Invercargill after a suspected bird strike when it left Queenstown Airport last night. The plane bound for Melbourne made a safe landing and none of the 73 passengers and crew on board were injured. . A runway inspection was completed minutes before last night’s incident and no birds were detected at that time. It is the second bird strike incident at Queenstown in a month after an Air New Zealand aircraft aborted a take-off in May.

What happens when a bird hits a plane?

“It depends on the pilot’s reactions, what kind of bird, and where the bird hits the aircraft,” says Lizzie Civil, chairwoman of the New Zealand Aviation Wildlife Hazard Group (NZAWHG).

A strike to the nose cone will be expensive, but not fatal.

If birds are ingested into both engines, it could be a different story, she says in a Civil Aviation Authority (CAA) publication. This was famously illustrated when a US Airlines flight had two engines knocked out on take-off from New York, but landed safely in the Hudson River.

Aircraft engines are designed to withstand ingesting birds and tested with frozen chickens or turkeys, but larger animals or a flock of them can destroy engine components as they are sucked through.

Twin-engine aircraft are also designed to fly safely on one engine as the Virgin Australia aircraft did when it diverted to Invercargill, which has a longer runway and a less challenging approach than Queenstown Airport.

The New Zealand Air Line Pilots Association (NZALPA) president Andrew McKeen, also a 787 pilot, said that while flames appeared to emanate from the rear of one of the engines, the aircraft or engine was not actually on fire.

“The damage caused by the bird strike would have disturbed the airflow through the engine creating a compressor surge or stall. This results in excess fuel being burnt as it exits the engine and this is what was visible to those in the aircraft and on the ground,” McKeen said.

“Specific pilot training for such incidents was thorough and frequent, and any pilot operating into Queenstown would have been through training specifically related to Queenstown airport.’'

New Zealand Airports and the wider aviation industry have long recognised the risks from bird strikes.

‘‘Each airport has a wildlife management programme, but no programme totally eliminates the risk.’'

The CAA says when planes hit birds, the forces are sufficient to also badly dent or tear open aircraft surfaces, shatter windscreens, rupture hydraulic lines, damage oil coolers and air intakes, smash landing lights and wreck sensor tubes.

When a small aircraft travelling at 90 knots (166km/h) hits a 500g bird, energy on impact is 536 joules.

But if speed is doubled, as with a commercial plane, the energy of the impact is quadrupled. Birds aren’t sucked into engines — they end up in one only if there is direct alignment between the flight paths of the engine and the bird.

How common are bird strikes?

Lizzie Civil says New Zealand is doing fairly well with bird avoidance. Its bird strike rate at airports is about four in 10,000 aircraft movements.

“Of course, that strike rate could be four sparrows. That’s likely not going to cause much damage to a plane. Whereas a Canada goose could be catastrophic,” she says.

Birds of primary concern are large in size, flocking birds that are slow flying, less manoeuvrable or erratic, such as plovers, Canada geese and black swans.

Secondary concerns are species of small-to-medium size that habitually hunt or forage on or over the airfield, like hawks, starlings, gulls, and waterfowl or birds such as wading species, which habitually fly across the airspace.

At some New Zealand airports, rabbits, too, can be a problem. It is not yet known what birds were in the Queenstown Airport area when the Virgin Australia aircraft took off last night. Queenstown Airport says during the past 12 months there have been an average of 3.4 bird strikes a month.

The most common species are finches and plovers. It’s possible that it was a duck strike (mallard) but this is yet to be confirmed. Duck strikes are very rare. There has not been one reported this year. There was one duck strike reported in 2023, which was in September, said an airport spokeswoman.

American Scientist reports in the United States a bird-strike event has been estimated to occur about once every 2000 flights, depending on the time of year and location. But many events are not reported.

When do bird strikes happen?

The CAA says most bird strikes happen between 50-800ft (15-243m) on take-off and landing — the most critical time of flight for pilots.

The highest bird strike occurred off the West African coast at 37,000ft (11,200m) when a plane hit a bearded vulture.

Jet turbine engines are more vulnerable than piston engine propeller planes because of their greater speed and lower noise level ahead of their flight path. Birds don’t get enough warning to take evasive action, and when disturbed on the ground tend to swarm up in alarm.

Bird’s-eye view

The CAA says the more visible an aircraft is and the more time a bird has to see or hear it, the greater the possibility the bird will get out of the way.

“An interesting twist is that when an aircraft is turning, birds cannot predict its flight path and many strikes have occurred in this situation with the birds apparently flying directly into the aircraft’s path.”

Birds are not instinctively equipped to cope with aircraft and their reaction varies. Some waders will rest and feed only a few metres away from taxiing or departing aircraft.

If it becomes necessary to move to avoid being run down, the birds may fly off a few metres and continue feeding. But, if startled by an unusual movement or noise, they may take to the air in panic and fly into the path of the aircraft.

Some birds will occasionally try to outfly an aircraft, turning out of its flight path only at the last second. A hawk may even attack an aircraft, viewing it as potential prey when seen from a great distance, and discovering its error too late, the CAA says.

The US Airways Airbus A320 flown by Captain Chesley "Sully" Sullenberger who landed it safely in the Hudson River after both engines were knocked out by geese in 2009. Photo / AP

What’s being done to prevent bird strikes?

At Queenstown Airport there are several operational processes in place to deter birds from the airfield and surrounds. Bird activity varies with in different seasons and bird migratory patterns.

‘‘We have a wildlife management plan, which includes managing grass to keep it at an optimal height to be less desirable to birds. We also spray and use seed that has a bird deterrent factor to reduce food sources to stop birds from settling on the airfield. We also use gas cannons, lasers, acoustic machines, and pyrotechnics to scare birds away,’' said a spokeswoman.

The company works with neighbouring properties to reduce risk of birds settling near Queenstown Airport.

Generally unnatural sounds such as loud bangs, and natural sounds such as bird distress calls, all work to some degree as scaring devices.

Because birds have the same hearing range as humans, noises that birds find alarming soon become offensive to us.

This harassment loses its effect on birds if repeated without any harm being done, so it becomes necessary to reinforce this with periodic shootings, says the CAA.

Birds are easily frightened, but they are also faced with the alternative that they must feed or perish, so they learn to live with some degree of anxiety and ignore threats to their safety

NZAWHG regularly meets airports to discuss how to reduce the risks of aircraft versus bird. Civil is the former wildlife and ground manager at Auckland Airport, and was an airfield environmental officer at NZDF Whenuapai. She says in the past, the approach to birdlife at airports was very much reactive culling.

“But culling some territorial airport wildlife that are, at least, used to that environment and act in predictable ways, just leads to non-airport-savvy wildlife coming in and acting erratically, and causing an even higher risk to aircraft.’’

She says her group has managed to change the mindset of many aerodrome owners and operators, to a more proactive one that preserves the environment while managing problematic species.

“What we do is manage the airport ecosystem, so it’s less attractive to whatever species may be a high risk to aviation.”

Often that includes building alternative habitats for the birds elsewhere, like bird roosts. And making sure any development near the airport doesn’t include bird-attracting features like flat roofs, and seeding, fruiting, or large roosting trees.

She says in some cases, culls are necessary if the birds are categorised as high risk and their numbers are increasing.

Grant Bradley has been working at the Herald since 1993. He is the Business Herald’s deputy editor and covers aviation and tourism.