This weekend’s devastating aircraft crash in South Korea on Sunday has shone a light on the risks that bird strikes pose to aviation.
While the cause of the Jeju Air Boeing 737 crash at Muan International Airport, in the south-western province of South Jeolla, has yet to be confirmed, authorities have indicated that a bird strike and bad weather are thought to be to blame.
With 179 of the 181 people on board the Boeing 737-800 people on board killed, the incident – South Korea’s worst domestic civil aviation disaster – could be the most lethal on record caused by a bird strike.
According to reports, the right-hand engine may have been damaged and, after landing, the aircraft careered along the runway without its landing gear down before crashing into a wall and bursting into flames.
South Korea's Land Ministry said in a briefing that an airport control tower had warned of a bird strike at 8:54am. The pilot declared mayday at 8:59am and landed the plane at 9:03am without the landing gear deployed.
Frequent occurrence
Mark Pilling, the managing editor of Arabian Aerospace, said that bird strikes were “a common occurrence” with aircraft and it was “exceptionally rare” for them to cause major incidents.
“It’s a common thing that occurs on a routine basis at airports globally,” he said. “It’s not unusual that there are bird strikes in general.
“Pilots routinely train for bird strikes and what they mean to the aircraft … It’s something that they are ready for.”
Most bird strikes occur around take-off and landing, because when aircraft are cruising they are typically at altitudes much higher than those at which birds are found.
Mr Pilling said that aircraft engines were certified to be able to withstand bird strikes. However, there are rare situations, such as if an aircraft strikes a flock of large birds, where engine failure can happen.
One of the most high-profile bird strike incidents happened in January 2009 and involved US Airways Flight 1549, which lost power in both engines after hitting a flock of Canada geese shortly after taking off from LaGuardia Airport in New York.
The pilots guided the Airbus A320 into the Hudson River, where all 155 people on board were evacuated. While there were many injuries, some serious, no one was killed.
Sully: Miracle on the Hudson, a Clint Eastwood-directed film named in honour of the plane’s captain, Chesley Sullenberger, and with Tom Hanks in the starring role, was a box-office hit when it was released in 2016.
Reports from 2017 indicated that after the river landing, nearly 70,000 birds were killed in the New York area to reduce the likelihood of subsequent bird strikes.
Another major incident happened in 1960 in Boston in the US, when a Lockheed 188A Electra hit a flock of starlings and, the author David Gero wrote in his book Aviation Disasters, “a large number of the birds were ingested into three of its four engines”.
The plane was rolled into a spin and plunged into the Boston Harbour inlet just a minute after taking off, killing 62 of the 72 people on board. The two cabin crew were among 10 survivors.
Until this weekend’s incident, the cause of which has yet to be confirmed, the Lockheed 188A Electra crash in Boston was thought to have been the worst-ever bird strike incident.
Costly incidents
Reports indicate that there were more than 17,000 bird strikes in the US alone in 2019 and, globally, they have been estimated to cause the aviation industry $1 billion a year, according to a 2020 paper, The Bird Strike Challenge, published in the journal Aerospace.
In the study, Dr Isabel Metz and her co-authors wrote that up to late 2019, bird strikes had caused 618 hull losses and 534 deaths since the beginning of aviation – with the first recorded bird strike dating back to 1905.
Bird strike rates vary between country but in recent years, the researchers said, they had been recorded at between 2.83 and 8.19 per 10,000 aircraft movements.
In civil aviation, between 2 per cent and 8 per cent of bird strikes damage the aircraft, with between six and seven per cent having “a negative operational effect on the flight”, according to Dr Metz and her co-authors.
Testing the engines
To prevent bird strikes, larger airports in particular make efforts to keep birds away, Mr Pilling told The National. Examples of the measures they take include using birds of prey, lights and lasers, and the playing of bird distress calls.
To ensure that aircraft can withstand most incidents, in tests, bird corpses are catapulted at high speed towards vulnerable parts of aircraft, including, wing and tail sections, windscreens and engines, according to material published by the Bird Strike Association of Canada.
Writing in 2009, Dr John Downer, a research officer in the Centre for Analysis of Risk and Regulation at the London School of Economics, said that aircraft engines cannot realistically be protected by grilles, because a structure able to withstand birds would disrupt airflow and “pose its own risk of being smashed into the blades”.
Instead, engines are made to be “incredibly tough”, with turbine blades representing “the very forefront of materials science”.
Standardised tests involve projecting into engines, at speeds similar to those seen during take-off and landing, fresh chicken corpses, some of which may weigh up to about 4kg when larger engines are being tested. Other tests involve multiple bodies of smaller birds.
Previously, frozen bird corpses were used, however Dr Downer said testers prefer not to use these any more because such bodies could contain “dense ice particle” or be dehydrated from thawing.
“If the turbine disintegrates or catches fire … if the ‘pilot’ cannot shut it down afterwards or if it releases blade fragments through the engine housing, then the engine fails the test,” Dr Downer wrote of tests involving chickens, with stricter performance rules applied when smaller birds are used.
Sometimes artificial birdlike objects made from gelatin are used instead of the bodies of actual birds.
Dr Downer indicated that the tests did not cover all potential real-life scenarios, such as when hundreds of smaller birds are inhaled by engines, or when aircraft encounter flocks of larger birds.
