Distortion of the electronic signal emitted by the landing aid equipment caused a China Airlines “Jumbo” to initiate an approach procedure off the runway and hit the grass next to the tarmac at Chicago Airport.
The conclusion of the incident, which occurred on June 21, 2018, is contained in the final report of the National Transportation Safety Board (NTSB), published this Saturday (21).
The incident captured by the terminal’s cameras shows the huge aircraft hitting its wheels on the grass next to the runway and then going into a goaround. This type of event is called a runway excursion.
The image can be seen from the 27 seconds of the video. In the upper right corner the touch of the Boeing 747 appears on the lawn and shortly after that the dash.
China Airlines Boeing 747400 Freighter, registration B18711, was on flight CI5148 from Anchorage, Alaska to Chicago O’Hare, USA.
There were four crew members on board. At 09:57 (14:57Z) the aircraft was on an instrument landing system (ILS) approach to runway 10L.
Shortly after the incident, the jumbo pilots warned that they would go down on the runway due to a shortterm deviation.
The crew of another taxiing aircraft informed the tower that the jumbo had left the runway. And a third crew claimed the need for a runway inspection [para o caso de alguma peça do Jumbo ter se soltado durante o impacto].
According to the Aviation Herald, a runway inspection confirmed the suspicion and found debris at the scene. The Wind Direction Indicator (WDI) windsock was found damaged.
The route was closed for about 50 minutes.
The China Airlines jumbo positioned for another approach and landed safely on another runway, 09R, approximately 25 minutes after takeoff.
An excerpt from the NTSB’s final report on the probable cause of the incident reads:
“Interference with the locate signal that resulted in a multipath condition that occurred during an ILS CAT III approach (autoland). This condition resulted in a runway deviation and subsequent goaround.”
Multipath is a term used to describe the distortion of the radiated signal.