Incident Overview
On December 12, 2022, at approximately 11:31 Japan Standard Time, a Cessna 172P (registration JA4121) operated by SGC Saga Aviation Co., Ltd. was conducting a flight training approach to Saga Airport. During the landing approach, a vehicle entered the runway, prompting the aircraft to execute a go-around. The closest distance between the vehicle and the aircraft was about 2,360 m.
Aircraft and Personnel
The aircraft involved was a Cessna 172P, serial number 17276178, manufactured on January 16, 1984. The captain (trainee) was a 21-year-old male holding a private pilot certificate. The instructor was a 57-year-old male with a commercial pilot certificate. The bird sweep staff was a 74-year-old male who had attended restricted area safety training on March 30, 2021. The Air Traffic Service Flight Information Officer was a 36-year-old male with an air traffic service flight information officer certificate.
Sequence of Events
At 11:28:30, the Air Traffic Service Flight Information Officer advised the aircraft that the runway was clear. Subsequently, the Saga Prefecture Saga Airport Office requested the vehicle to perform a runway bird sweep. At 11:30:00, the vehicle acknowledged. At 11:30:44, the vehicle requested permission to enter the runway. The Air Traffic Service Flight Information Officer responded at 11:30:55, instructing the vehicle to hold position because of an arriving aircraft. However, at 11:31:01, the vehicle made a wrong read-back stating "Cleared enter runway, Roger" and entered the runway. At 11:31:07, the officer again instructed the vehicle not to enter, but received no response. At 11:31:16, the officer advised the aircraft to go-around, which the aircraft acknowledged at 11:31:26. The vehicle vacated the runway at 11:32:44.
The bird sweep staff stated that after many birds were observed, he hurried to the runway upon request. He believed entry was permitted due to a response. He used a portable radio on frequency A, while the airport office used frequency B. The volume on the portable radio was later found set to 10, lower than the typical setting of 18.
Analysis
According to the investigation, the vehicle stopped briefly at stop lines but entered the runway while the driver was talking on the radio. The bird sweep staff misheard the hold instruction as permission to enter. It is probable that he mistakenly believed permission was granted because he was driving and talking, and because similar requests rarely resulted in a hold. The use of frequency A instead of frequency B may have contributed to the miscommunication.
Safety Training
The airport office required biannual recurrent training for drivers operating in the airport. However, bird sweep staff were mistakenly omitted from the recurrent training request list.