[News Terms] Aircraft Landing Guidance Facility 'Localizer'

Regarding the Jeju Air passenger plane disaster that resulted in 179 deaths, an analysis is emerging that the concrete mound-shaped localizer installed at the accident site, Muan International Airport in Jeollanam-do, exacerbated the damage.

Localizer (Localizer·azimuth facility) is an antenna-shaped facility installed at the end of an airport runway. When it sends radio signals to align the aircraft with the runway centerline, the aircraft can accurately approach the runway laterally. It is an important device that helps aircraft land safely, especially in bad weather or limited visibility conditions, and is considered a core element of the airport's Instrument Landing System (ILS).

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Generally, localizers are installed as steel frame structures. Even if an aircraft passes over the runway and reaches the localizer, it must be made of materials that break easily to minimize collision damage.

According to the International Civil Aviation Organization (ICAO) regulations, "all structures near the runway approach area must be designed to break easily." Article 25 of the Ministry of Land, Infrastructure and Transport's detailed guidelines for managing aviation obstacles also states that airport equipment and support facilities that could become obstacles, such as localizer antennas, must cause minimal damage to aircraft in the event of a collision. It explains that the structure should maintain structural integrity and robustness up to the specified maximum load, but beyond that impact, it should be designed to break, deform, or fail in a way that poses minimal risk to the aircraft.

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However, the localizer at Muan Airport was installed on a 2-meter-high concrete mound about 300 meters away from the runway end. The mound supporting the localizer at Muan Airport appeared to be a dirt heap on the outside, but inside, there were 19 wide plank-shaped concrete pillars densely embedded. When a plane collides, the mound should collapse to minimize impact, but on top of these pillars, a large concrete slab measuring 42 meters wide, 4.2 meters long, and 30 centimeters thick was placed, making the structure as solid as a fortress. The mound, which was expected to absorb impact because it was made of soil, is pointed out to have instead amplified the impact, leading to the disaster.

The Ministry of Land, Infrastructure and Transport explained on the 30th of last month regarding the controversy that the accident aircraft collided with the localizer installed on concrete, worsening the accident, stating that "it was installed according to relevant regulations." According to the Airport Facilities Act, "all equipment or installations considered obstacles on airport grounds must be mounted on breakable supports," but the Ministry explained that this regulation applies only when located within the runway end safety area, so the localizer at Muan Airport, installed outside the end safety area, does not violate the regulation.

However, the Ministry's "Standards for Airport, Airfield Facilities, and Runway Installations" states that for "precision approach runways," the end safety area should be extended to the localizer installation point, and Muan Airport's runway was designed as a precision approach runway. Accordingly, there is an analysis that the end safety area of Muan Airport extends to where the localizer is located. The Ministry has stated it will review the regulations again.

Meanwhile, to determine the cause of this disaster, the Jeollanam-do Police Agency's Jeju Air Passenger Plane Accident Investigation Headquarters conducted a search and seizure on the 2nd at the Muan International Airport department office, control tower, Busan Regional Aviation Administration Muan branch office, and Jeju Air Seoul office. The police are securing materials such as the appropriateness of the runway structures (localizer) that collided with the accident aircraft, communication between the control tower and the pilot just before the accident, and the maintenance history of the accident aircraft.