Explainer: Embankment bearing brunt of blame in Jeju Air crash

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Explainer: Embankment bearing brunt of blame in Jeju Air crash

Published: 31 Dec. 2024, 17:44 Updated: 31 Dec. 2024, 18:39

SARAH CHEA
[email protected]

Audio report: written by reporters, read by AI

Fire authorities search for remains among the debris of the crashed Jeju Air plane separated by smashed localizers at Muan International Airport in South Jeolla on Dec. 31. [YONHAP]

From bird strikes to a landing gear malfunction, the potential causes behind the deadly Jeju Air crash offered by Korean authorities — albeit not yet certain — have raised more questions than they answer.

Such events are regarded as neither extremely rare nor necessarily responsible for the staggering number of fatalities recorded in the Dec. 29 disaster that claimed 179 lives, the deadliest aviation accident ever on Korean soil.

This has led experts, local media outlets and the general public to gradually zero in on a concrete structure at the south end of the runway that propped up a set of localizers, antennas designed to guide aircraft safely during landings, that resulted in an explosion as the plane struck it.

With the Ministry of Land, Infrastructure and Transport saying that decoding the collected black boxes from the aircraft could take up to six months in a joint investigation with the U.S. National Transportation Safety Board and Boeing, the manufacturer of the 737-800 at the center of the disaster, the door remains open for many other variables to emerge as the reason behind the fatal incident.

Q. What exactly happened to the aircraft during the critical nine minutes before the accident?

A. The Jeju Air jetliner received permission to land from the south from the control tower at Muan International Airport at around 8:54 a.m. But three minutes later, it received a bird strike warning, alerting the pilots to a potential collision with a bird or flock of birds.

At 8:59 a.m., the pilot declared a mayday three times and notified the control tower that the plane would make a go-around due to bird strikes.

However, it failed to make a full turn and made an approach from the north without the deployment of its landing gear. Unable to reduce its speed as it skidded on the runway, the plane crashed into a concrete embankment holding localizers, bursting into flames upon impact.

The whole process occurred in just nine minutes after the control tower gave it the green light to land, and five hours after it took off from Bangkok, Thailand, carrying 175 passengers, mostly travelers returning from Christmas trips, along with six crew members.

A Jeju Air airplane burst into flames after it veered off the runway and hit a concrete embankment at Muan International Airport in south Jeolla on Dec. 29. [YONHAP]

What’s the concrete structure and why is it being mentioned as the primary culprit behind the severity of the accident?

It was disclosed that the jetliner exploded into flames after it hit a localizer set up 251 meters (823 feet) from the runway's end.

The problem was that the localizer was on top of a two-meter-tall concrete embankment, in stark contrast to other airports that set up the brittle structures — which can easily be taken out by airplanes upon contact — on level terrain.

“It’s certain that the concrete mound worsened the accident and seriously increased the severity of the damage,” said aeronautical science professor Kim Kwang-il of Silla University. “I’ve visited runways in many different countries and have never seen anything like that.”

“If there was no structure, or at least if it was made with lighter materials, the airplane could be moved forward, minimizing casualties.”

Kim added that the structure may violate International Civil Aviation Organization (ICAO) rules, which stipulate that such hard structures must be located a certain distance away from the runway.

“The localizer appears to have been built in violation of the guidelines, and this will be another key issue in the investigation,” Kim said.

The Transport Ministry, however, has denied such assertions, arguing that the wall does not violate any regulations.

“Korean laws and even ICAO rules don’t specify the distance or materials of supporting structures for the antennas,” said Joo Jong-wan, director of aviation policy at the Transport Ministry, during a briefing on Monday. “Similar concrete structures exist at airports like Yeosu and Cheongju.”

The tail section of the crashed Jeju Air airplane, a Boeing 737-800, is assessed by authorities at Muan International Airport in South Jeolla on Dec. 30, a day after the fatal incident that killed 179 passengers and crew. [YONHAP]

Why did the Muan airport have such an unusual structure?

Muan International Airport is on terrain that declines after the south end of the runway. For this reason, the Transport Ministry set up an embankment to level off the terrain, and set up a localizer on top of it.

“There can be no explanation other than that the people in charge were negligent when designing the structure,” said Prof. Hwang Ho-won of the Korea Aerospace University, who also serves as the chairman of the Korea Association for Aviation Security. “It’s an airport in a rural area, so they were careless. Incheon and Gimpo international airports never have such solid barriers near a runway.”

“It’s a big mistake and absolutely abnormal. The airplane might not have exploded, and the number of victims could have been far fewer without the structure.”

In fact, a Korean Air plane hit a localizer made of lightweight material at Mactan-Cebu International Airport in October 2022, but all 173 passengers and crew onboard survived.

An Asiana Airlines also hit localizer antennas at the airport in Hiroshima, Japan, in 2015, but again, there were no casualties.

Families of a Thai national, the victim of the airplane crash, mourn in front of Muan International Airport in South Jeolla on Dec. 31. [YONHAP]

Is the possible bird strike a contributor to the crash?

A bird strike could be the instigator of the crash, but cannot be the sole reason behind the mass fatalities, experts say.

Bird strikes are a relatively common hazard, but are rarely linked to fatal plane accidents.

“The crashed airplane belly landed without all three landing gear units, which is an unprecedented result if a bird strike was the only cause,” said Prof. Hwang of the Korea Aerospace University. "The link between engine failure and landing gear inactivation needs to be investigated."

“But even if birds really caused an engine to fail, the other engine could deploy the landing gear, and even in the event that both engines failed, the pilot could manually activate the gear,” Hwang said.

In fact, the Transport Ministry also said there is "generally no correlation between engine and landing gear failures,” in a briefing held on Dec. 29.

There were a total of 623 bird strike cases between 2019 and the first half of 2024, according to data from the Korea Airports Corporation.

The United States suffers some 20,000 bird strike cases annually. In 2023 alone, a total of 19,400 bird strike cases were reported at 713 airports across the country, according to data from the Federal Aviation Administration.

But deadly accidents do occur due to bird strikes.

A battlefield radar plane carrying 25 U.S. and Canadian airmen crashed at an Air Force base in Alaska after a collision with geese in 1995, killing all on board.

"A bird strike is unlikely to have interfered with the deployment of the landing gear," said Robert A. Clifford, the founder and senior partner at Clifford Law Offices in Chicago who managed the legal case against Boeing over the 737 Max that crashed in Ethiopia in 2019, killing 157 people.

"This plane appears to have experienced a mechanical problem in what appears to have been a very reckless move. The pilot was authorized to attempt a landing without an operational landing gear, needlessly exposing all aboard to great danger that ended in this fiery crash,” Clifford added.

Food, soju bottles and messages are placed in front of Muan International Airport in South Jeolla to mourn the victims on Dec. 31. [YONHAP]

Why couldn't the airplane reduce its speed?

That’s linked to a possible mechanical problem that raises the possibility of an “in-flight shutdown,” when an engine ceases to function, whether self-induced or caused by an external influence, which severely compromises all functions related to speed reduction.

In a Boeing 737-800, there are various parts that play the role of brakes such as flaps, a high-lift device used to reduce the stalling speed of an aircraft wing; reverse thrust, a temporary reversal of propulsion of an aircraft's engines to counter the forward momentum of the aircraft; and speed brakes, a type of flight control surface used on an aircraft to increase drag.

All of those functions reportedly did not work in the Jeju Air crash, which means the shutdown caused the failure of the hydraulic system that activated them.

“A failure of both engines means that no electronic functions could work in the airplane,” said Prof. Choi Yeon-chul, chief of the Korea Aviation Academy run by Hanseo University.

The Transport Ministry cautiously mentioned the possibility of an in-flight shutdown during a briefing but added that “confirmation can be made after a thorough analysis of the black boxes collected from the airplane.”

The manufacturer of the engine, CFM International, a joint aircraft engine production venture between GE Aerospace and France’s Safran Aircraft Engines, is currently in talks with the Korean government to join its ongoing probe.

Fire authorities search for remains among the debris of the crashed Jeju Air plane at Muan International Airport in South Jeolla on Dec. 31. [JANG JIN-YOUNG]

What about claims that the runway was too short?

While it’s short compared to other international airports, that wasn't really the problem, experts say.

The Muan airport’s runway extends 2.8 kilometers (1.7 miles), which is shorter than Incheon’s 3.95 kilometers and Gimpo’s 3.6 kilometers, but longer than other airports in rural areas like Yangyang airport’s 2.5 kilometers and Cheongju airport’s 2.7 kilometers.

“The length of the runway abides by the rules and can’t be a contributor to the incident,” Prof. Hwang added. “In normal cases, a Boeing 737 jet could land in even on a 1.8-kilometer runway.”

Any possibilities regarding the inexperience of the pilots?

Experts remain skeptical about claims concerning the pilots, rather saying that they did their best to land safely.

The pilot of the crashed plane had 6,823 hours of flight time, while the copilot had 1,650 hours, both in excess of the U.S. Federal Aviation Administration's 1,500-hour requirement for commercial pilots.

“It appears that the pilots, who also died due to the incident, did all they could, such as attempting a go-around to make as smooth a landing as possible,” Prof. Kim of Silla University said.

“But of course, it’s important to determine the exact intentions of the pilots through the voice recorder collected from the airplane to discover the exact situation at that moment,” Kim said. “For now, however, they cannot be the target of blame for the unfortunate incident.”

Jeju Air also dismissed the argument, saying that “not all copilots are promoted to pilots; only those with 3,500 hours of flight time are deemed eligible for promotion” in defense of the captain of the flight.

BY SARAH CHEA [[email protected]]