What happened
On March 31, 2014, a China Airlines Boeing 747-400F, registration B-18721, operating flight CI 6416 from Abu Dhabi to Taoyuan International Airport, veered off the runway during landing. The flight crew, consisting of one captain and two first officers, had decided to use a Flap 25 configuration for the landing due to the high landing weight and intended to use autoland procedures.
During the approach to runway 23R, an aircraft departing on the same runway passed through the sensitive area of the Instrument Landing System (ILS) antennas. This caused interference with the navigation signals. As the aircraft approached the runway, the localizer indications began to deviate, and the aircraft developed a rightward bank of up to 5.6 degrees. The aircraft touched down to the right of the centerline with a 2.5-degree bank. During the rollout, the right main gear exited the runway edge, traveling approximately 1,400 feet before returning to the paved surface. The excursion resulted in damage to six runway edge lights and one taxiway edge light.
The investigation
The Taiwan Transportation Safety Board (TTSB) investigated the sequence of events, focusing on the navigation signal integrity and crew response. The investigation established that the crew did not notify the tower of their intent to use autoland and failed to verify if the ILS sensitive area was protected from interference. Furthermore, the investigation found that the crew did not realize the aircraft had exited the runway until after the aircraft had returned to the pavement, and they did not report any abnormalities to the ground staff upon arrival. The investigation also noted that the cockpit voice recorder (CVR) data from the time of the accident was unavailable because the aircraft's electrical power was not disconnected during subsequent maintenance and pre-flight checks, causing the data to be overwritten.