• Combination of technical, operational and environmental factors extending beyond reported bird strike led to deadly crash, aviation expert tells Anadolu
• It is less common for a bird strike to directly damage the landing gear, but they 'can indirectly cause landing gear malfunctions if they damage hydraulic lines, control systems or related components,' says Marco Chan 

ISTANBUL 

Following a plane crash Sunday in South Korea that killed 179 passengers and crew, the focus is now on investigations into the accident, with various theories -- from bird strikes to other complicating factors -- being evaluated by analysts around the globe.

Reports suggest that local authorities investigating the crash of the Jeju Air Boeing 737-800 at Muan International Airport are pursuing the possibility of a bird strike as the cause.

A Jeju Air pilot reportedly told air traffic control that the passenger plane "suffered a bird strike before it crashed."

Experts, however, believe that a bird strike alone cannot be the sole cause of the accident.

"The Jeju Air crash likely resulted from a combination of technical, operational and environmental factors extending beyond the reported bird strike. One key focus will be system failures," Marco Chan, a senior lecturer in aviation operations at Buckinghamshire New University, told Anadolu.

According to Chan, the bird strike appears to have been a "contributing factor," and the crash -- one of the worst disasters in the country's aviation history -- likely involved "multiple interrelated issues."

How deadly are bird strikes?

Highlighting the frequency of bird strikes in aviation, Chan, a former pilot, said that over 13,000 are reported annually worldwide, according to the International Civil Aviation Organization (ICAO).

But compared to the approximately 40 million commercial flights operated globally each year, a pre-pandemic figure from the International Air Transport Association (IATA), a bird strike occurs in roughly one out of every 3,000 flights, he added.

"Most bird strikes cause no significant damage, as modern aircraft are built to withstand such events. However, certain factors can increase the risk," he said.

"Larger birds or collisions with multiple birds are more likely to cause damage, especially if they strike engines, windshields, or critical systems like control surfaces or hydraulics."

Elaborating further, Chan said that aircraft speed amplifies the energy of the impact, and bird strikes often occur during takeoff or landing, when response time is limited.

Severe cases such as engine failure or loss of system functionality can test the limits of an aircraft’s design and a crew’s decision-making under pressure, he added.

While rare, there have been catastrophic incidents involving bird strikes, he said.

"US Airways Flight 1549 in 2009 suffered a dual-engine failure after ingesting a flock of geese, resulting in a safe emergency landing on the Hudson River with no fatalities.

"Conversely, in 1960, an Eastern Air Lines Lockheed Electra crashed due to a bird strike, leading to fatalities. These examples show that while bird strikes seldom lead to crashes, under certain conditions, they can escalate into severe emergencies," he added.

Can a bird strike damage landing gear?

While reports suggest that the malfunction of the landing gear in the Jeju Air plane is being linked to the bird strike, Chan believes that it is less common for a bird strike to directly damage the landing gear.

This is due to its position and design, which is typically more shielded than engines or windshields, he said.

"However, bird strikes can indirectly cause landing gear malfunctions if they damage hydraulic lines, control systems, or related components," he noted.

Citing an example, Chan said that if a bird is ingested into an engine, it can cause significant damage, potentially leading to engine failure. This can result in hydraulic pressure loss if the affected engine powers the hydraulic system, preventing the landing gear from deploying properly.

According to Chan, modern aircraft like the Boeing 737-800 have backup systems for such scenarios, including the landing gear alternate extension procedure outlined in the Quick Reference Handbook (QRH), a quick-access manual for aircraft pilots that contains all the procedures applicable for non-normal and emergency conditions in an easy-to-use format.

"This allows pilots to manually deploy the landing gear using gravity in the event of hydraulic failure. However, this may not work if the bird strike caused direct damage to the landing gear mechanism or critical hydraulic components," he said.

Richard Curran, a professor of aviation management at City University of London, believes that it is unlikely that a bird strike could lead the landing gear to malfunction.

He also called the landing gear not being deployed “highly unusual,” as there are hydraulic systems with backup.

“Also, the landing gear is actually designed to go down also under gravity, freefall. That's part of the certification. So why did that not happen? Something had to be jamming it,” he said.

"We were sure of course, also that there were failures from the technical mechanical systems because there was no landing gear, there were no visible flaps, there was no use of thrust reverser."

Speaking about the manual feature of the landing gear, Curran highlighted that the landing gear itself, which is very heavy, can actually be deployed under its own weight.

"So the only reason that that was not deployed is that something was stopping it from extending. So there was a blockage of some nature that would not be caused typically, of course, by a bird strike.

"I don't know from the bird strike that that caused damage and that it caused damage to other interrelated systems, but it is very unlikely," he said, adding the birds would not have been anywhere near the landing gear, as the landing gear was safely stowed on takeoff.

"I think something blocked the landing gear, or at the very least stopped the signal being given to the system to deploy...The signal, the intent from the pilot to deploy has not reached the gear, or it has and it has not been able to, it has been blocked in some way," said Curran.

"The blockage thing from a bird is highly unlikely, and that damage caused by a problem in the engine to the system that links to the hydraulic deployment is also highly unlikely."

Curran pointed out that the landing gear is something which is highly maintained, and that will be a big part of the investigation.

“The landing gear is so critical to takeoff and landing, which are the two most dangerous phases of flight, and obviously there's lots of potential fatigue issues. So it can suffer from fatigue.

"I think it's very important to look at the maintenance and how well that aircraft in particular was being maintained and the fleet that it belongs to is being maintained," he added.

Investigation

Chan also pointed out how the investigators will closely examine whether the bird strike directly or indirectly affected systems connected to the landing gear, including hydraulic lines and mechanical components, and whether engine ingestion played a role in cascading failures that led to the malfunction.

"Investigators will determine if the bird strike caused cascading issues, such as hydraulic failures, that affected the deployment of landing gear, slats, or flaps—critical systems for deceleration and stability during landing," he said.

He also pointed out how the timeline of events in the deadly crash was another crucial aspect, with investigators to access whether more time for troubleshooting and preparation could have changed the outcome.

"A bird strike warning was issued at 08.57 local time, followed by the crew’s mayday declaration at 08.58. The crash occurred five minutes later, at 09.03. This compressed timeline suggests the aircraft was in a critical condition, requiring a rushed landing."

Experts are also questioning the presence of a concrete wall, highlighting how runway and approach factors are also crucial in the investigations.

"Runway 19, where the crash occurred, has a -0.2% downhill slope, which increases the landing distance required. Combined with potential system failures, this may have contributed to the runway overrun.

"The concrete fence 300 meters beyond the runway end will be reviewed, as such barriers should ideally be frangible—designed to break on impact—to minimize damage during overruns," he said.

Highlighting that although weather conditions were reportedly calm and clear according to the Meteorological Aerodrome Report (METAR), Chan said that this will still be examined to rule out unexpected environmental influences.