The Boeing 747 in flight, in the scene of the video featured in this article
This Saturday, May 21, 2022, the United States National Transportation Safety Board (NTSB) released its final report on the probable cause of the serious incident in which a jumbo jet plane landed on the side of the runway, leading to some Damage resulted before it flew around and returned to a safe landing.
At that time, on June 21, 2018, the Boeing 747400F (freighter), registered under registration B18711, operated by China Airlines, as reported by the Aviation Herald, operated flight CAL5148 between Anchorage and Chicago O’ Hare by , both in the US, with 4 crew members.
The aircraft performed an instrument approach (ILS) to runway 10L at 09:57 local time (14:57Z) with visibility impaired by the weather, but at the time of landing the pilots warned the air traffic controller that they were entering the airway a deviation from the track.
The video below shows the jumbo approaching and landing on the side of the runway, taxiing across the grass for a few seconds and passing close to other aircraft that were parked on the adjacent taxiway:
The crew of another plane on the ground reported noticing the Boeing 747 had veered off the runway. A third crew informed the tower that the runway needed to be inspected.
The runway inspection found debris on it. In addition, the windsock (WDI) to the left of the runway, between taxiways DD and N1, was found damaged. The runway was closed for approximately 50 minutes, during which time pilots positioned the 747400 for another approach and landed safely on runway 09R approximately 25 minutes after takeoff.
The aircraft was inspected with only minor damage and was out of service for about two weeks.
Among the analyzes performed by the NTSB during the investigation, the report highlights the following.
Flight CAL5148 was conducting an ILS autoland approach (autopilot landing) onto runway 10R. Instrument weather conditions at the time of the incident were 600 feet (182 meters) above ground level and visibility was 2 and 1/2 miles (4,000 meters) with moderate rain.
These conditions required air traffic control (ATC) protection of the critical area of the ILS, which was done in accordance with FAA Order JO 7110.65, Air Traffic Control. In this case, ATC will issue control instructions to avoid signal interference from vehicular traffic and aircraft taxiing with the ILS system when the reported weather is from a ceiling less than 800 feet or visibility less than 2 miles.
However, this limitation does not include taking into account takeoffs or landings of aircraft. So while an aircraft that took off earlier passed the critical area of the ILS, the Boeing 747 experienced localizer signal deviations on the short final approach for landing.
In the mathematical model analysis of this event, performed by the United States Federal Aviation Administration (FAA), the results were consistent with the localizer biases determined from the Jumbo Flight Data Recorder (FDR) data.
In particular, the modeling showed that a 1/4 mile deviation from the threshold would cause the aircraft to veer left during an automatic approach to land in order to continue on the course line indicated by the localizer.
The FAA Navigational Resources Engineer who performed the modeling wrote, “I am 90% confident that the launch location of flight ENY3544 caused sufficient multipath to generate a left flight display for CAL 5148 upon arrival .”
The NTSB report names the probable cause of the serious incident as follows:
Interference with the localizer signal, resulting in a multipath condition experienced by CAL5148 during an ILS CAT III approach (autoland). This condition resulted in a runway deviation and subsequent goaround. The interference was likely caused by an earlier takeoff flying through the critical area of the ILS while departing from the same runway.